Examination number: METE08001 METEOROLOGY: ATMOSPHERE & ENVIRONMENT 2013/2014. Mark %

Transcription

1 Examination number: METE08001 METEOROLOGY: ATMOSPHERE & ENVIRONMENT 2013/2014 Mark %

2 . CONTENTS General information Lecture and lab schedule Useful equations Table of constants Interpreting weather charts Stations plots Cloud identification and classification Calculations with the Saturation Vapour Pressure diagram Lab 1: Weather observations Lab 2: Plotting observations Lab 3: Wind chill Lab 4: Passage of a cold front Lab 5: Convection Lab 6: The skew T ln P diagram Lab 7: Thunderstorm analysis Lab 8: Radiation instruments Spare observations sheets Use of plagarism detection software and Own Work Declaration

3 Meteorology: Atmosphere and Environment Lab Book Assessment Lab Mark Comments Observations and plotting / 20 Wind chill / 10 Frontal analysis / 10 Convection tank / 10 Skew T ln P diagram / 10 Thunderstorms / 10 Radiation / 10 Overall lab-book presentation / 20 Total % 2

4 Course Organizer: David Stevenson Crew Building 314 Course Secretary: Meredith Corey Crew Building 215 Entrance requirements There are no specific entry requirements, but a physical approach to the subject is adopted throughout and some background in physics and maths, for example at SCE Higher grade (or equivalent), is desirable. Students who anticipate problems in this respect should discuss the matter with the Course Organizer. Class locations and times Lectures are 10:00-10:50 on Mondays, Wednesdays and Fridays in the Joseph Black Building (Chemistry) Lecture Theatre 100. Please collect a clicker from the new Murray Library and remember to bring it to all lectures; most lecturers will ask clicker questions. Lecture notes and other information will be posted on Learn. A large part of meteorology involves measurements, observations and practical experiments. This is the purpose of the laboratory classes, which commence during the second week of Semester 1 and are for 1½ hours a week on either Monday 14:00-15:30, Tuesday 10:00-11:30 or Thursday 14:00-15:30. You need to sign up for one of these sessions on Learn. The lab is room 8216 on the top (8th) floor of the James Clerk Maxwell Building (JCMB). The lift only goes to the 7th floor, and you need to ascend an extra flight of stairs. There is a separate lift between floors 7 and 8; let the Course Organizer know if you need to use this. Lab results should be recorded in this book, which you will hand in for marking at the end of the course. You will need a ruler, a pencil, a rubber and a calculator for every lab. Note that the only calculators approved by the College of Science and Engineering for use in exams are Casio fx82, fx83 or fx85. Recommended textbooks The main recommended text is Introducing Meteorology: A Guide to Weather by Jon Shonk ( ; also available as an e-book). This is a new book, and although the course doesn t exactly follow its contents, it covers much of the material at the correct level. There should be good stocks of this in Blackwell s, but it may not be in the library yet. In previous years, we have recommended Meteorology Today by C. Donald Ahrens (ISBN ), however this text has suddenly increased in price ( 104 in Blackwells!), so we no longer recommend students buy this. The 9 th edition (2009) is fine, and a free PDF can be easily downloaded (google: meteorology today 4shared). Second hand or library copies of earlier editions are fine, but be aware that any page references in lectures will differ between editions. Atmospheric Science: An Introductory Survey by J.M. Wallace and P.V. Hobbs is also recommended for students keen to take further Meteorology courses; this takes a more detailed maths/physics approach and goes beyond what is required for this particular course, but it is nevertheless an excellent book. There are copies ofthese latter two books in the library. Learning outcomes By the end of the course you will be able to: interpret weather maps in terms of local weather recognise cloud types and be able to describe their formation mechanisms plot and interpret vertical temperature and moisture soundings describe the basic processes occurring in the atmospheric boundary layer describe and explain the structure, physics and dynamics of thunderstorms, tornadoes and hail formation 1

5 describe the layers of the atmosphere from the surface to 100 km + explain the basic physics of atmospheric processes, such as radiation at the surface, water in the atmosphere and its phase changes observe and plot weather elements in standard format Assessment The course is assessed by coursework (30%) and an exam (70%) in mid-december. The coursework is divided equally between three components: a mid-term assignment (10%) a weather observations test in the last lab class (10%) this completed lab book, which must be handed in after the last lab class (10%). In addition, your lab book should be handed in after the third lab and you will be given feedback on the first three labs this will not count towards your overall mark, and you can subsequently revise your lab book for these three labs. The mid-term assignment will be posted on Learn on 7 th October and should be returned by 18 th October. The exam has two sections: Section A consists of 20 multiple-choice questions, together worth 40% of the paper, and Section B consists of 8 longer questions in 4 groups of 2; you must answer one question from each group, 4 in total, worth 15% each (NB this exam format was introduced in December 2012; earlier papers are slightly different). If more than 4 questions are answered in Section B, the highest marks from each group are counted. You will need an approved calculator (Casio fx82, fx83 or fx85) in the exam. To pass the course, you must obtain an overall mark above 40%, and get over 40% in both the exam and the coursework. There is a resit exam in August if you fail the exam. If you fail the coursework, your only option is to resit the coursework when it is offered the next year (NB this option requires the additional permission of the Head of School). The only exception is if you fail the coursework but have relevant special circumstances, in which case an alternative to the coursework will be offered. Past exam papers are available from Note (i) that the course content has varied slightly from year to year, and (ii) the new exam format. All items which count towards the degree assessment will be marked anonymously. You should enter your examination number, and not your name, on all such items (including this lab book). Please hand in items to the Course Secretary (Merdith Corey, Room 215, Crew Building) by 12 noon on the due date. There are penalties for late submission of work: a reduction in the maximum possible mark of 5% per day up to 5 days late, and zero marks for work that is more than 5 days late. University policies on plagiarism and other forms of cheating will be rigorously enforced for all assessments. Class Student Representative(s) One or more volunteers are sought to act as class representatives. The role of class reps is to help communicate any problems related to the course between the student group and the course team. In addition to ad hoc communications, you would be expected to collate any comments from students and present them at the staff-student liason meeting, held mid-semester. Contact the CO if you would like to volunteer. Problems If you are having problems with any part of the course, there are various things that you can do: 1. discuss it with a class colleague, and/or the class representative; 2. if the query is short, ask after a lecture or in a lab class; 3. arrange a time to see a member of staff. In the event of illness for more than a few days, or other disruption of study, please inform your Student Support Coordinator and the Course Organizer promptly. 2

6 Accessibility We welcome disabled students (including those with specific learning difficulties such as dyslexia) and are working to make all our courses accessible. If you wish to talk to a member of academic staff about the course requirements and your particular needs please contact the Course Organizer. You can also contact the Student Disability Service (Main Library, telephone , [email protected]) and an Advisor will be happy to meet with you. The Advisor can discuss possible adjustments and specific examination arrangements with you, assist you with an application for Disabled Students' Allowance, give you information about available technology and personal assistance such as note takers, proof readers or dyslexia tutors, and prepare a Learning Profile for your School which outlines recommended adjustments. You will be expected to provide the Student Disability Service with evidence of disability - either a letter from your GP or specialist, or evidence of specific learning difficulty. For dyslexia or dyspraxia this evidence must be a recent Chartered Educational Psychologist's assessment. If you do not have this, the Student Disability Service can put you in touch with an independent Educational Psychologist. If you feel that you need to use a calculator that is not on the currently permitted list, the Student Disability Service can assess your needs and suggest what alternative form of calculator may be appropriate as part of an agreed schedule of adjustments. If you require this document in an alternative format, such as large print or a coloured background, please contact the Course Organizer. The Course Team The course is delivered by three lecturers from the School of GeoSciences: Weather maps, observations and air pollution 12 lectures Prof David Stevenson ([email protected]) Crew 314 (Course Organiser) Air masses, fronts and radiation 8 lectures Dr Hugh Pumphrey ([email protected]) Crew 313 Atmospheric processes, clouds, thermodynamic diagrams and storms 10 lectures Dr Massimo Bollasina ([email protected]) Grant Institute 303 Course secretary: Meredith Corey ([email protected]) Crew 215 3

7 Feedback The University launched new Feedback Standards and Guiding Principles for staff and students in September 2010 ( For this course, individual written feedback and model answers will be provided for the mid-term exercise three weeks after the handin date. Preliminary written feedback on the lab books will be given in Week 5, and overall feedback on the lab books, weather observations test and exam will be available at the beginning of semester 2, and there will be an open feedback meeting on 5 th February. Lecturers will lead many of the laboratory classes and a post-graduate demonstrator will be present in all of the labs to give immediate feedback on work. Early in the semester, one or more volunteers will be sought to act as class representatives. They will have meetings with the Course Organizer to consider difficulties, complaints, suggestions etc. regarding the course. Make use of these representatives as a channel for your comments and feedback about the course. There will be a staff-student liason meeting mid-way through the course (date to be announced) to discuss any problems. 4

8 Lecture and lab schedule Week 1 16 Sept Monday 10am Wednesday 10am Friday 10am Weekly lab class (Mon, Tue or Thu) DS Introduction No lab DS Weather maps Satellite images DS Cloud classification Week 2 23 Sept DS Structure of the atmosphere DS Temperature measurements DS Humidity measurements DS 1. Weather observations Week 3 30 Sept DS Precipitation measurements DS Pressure and wind measurements DS Gas laws and thickness charts DS 2. Station plots Week 4 7 Oct HP Air masses and fronts 1 HP Air masses and fronts 2 HPAir masses and fronts 3 DS 3. Wind chill Week 5 14 Oct MB Condensation of cloud droplets MB Fog and cloud formation MB Precipitation from clouds HP 4. Weather fronts Week 6 21 Oct MB Physics of dry air MB Atmospheric moisture MB Atmospheric stability MB 5. Convection Week 7 28 Oct MB Atmospheric inversions MB Thunderstorms MB Hail, lightning and tornadoes MB 6. The skew T-ln P diagram Week 8 4 Nov Week 9 11 Nov Week Nov MB The Föhn effect Review HP Solar radiation and terrestrial radiation DS Air Pollution 1 HP Importance and nature of radiation HP Energy balance at the surface Diurnal variations DS Air Pollution 2 HP Perfect radiators Kirchhoff's law HP Rainbows and other optical phenomena DS Review/exam preparation MB 7. Thunderstorm analysis HP 8. Radiation instruments Exam tutorial DS Weather observations test 5

9 Useful Equations The ideal gas law: pv constant T relates pressure (p), volume (V) and Kelvin temperature (T) of a gas. Rather than volume, it is more convenient for meteorological applications to work with air density (ρ = mass/volume) found from The equation of state: p RT R is the specific gas constant. The dependence of the gas constant on specific humidity (q) in air is made explicit by p Rd ( q) T where R d = 287 JK -1 kg -1 is the gas constant for dry air. The hydrostatic equation: dp dz g gives the vertical gradient in pressure with height (z), assuming balance between pressure gradient and gravitational forces. Acceleration due to gravity, g = 9.81 ms -2. Combining the hydrostatic equation and the first law of thermodynamics gives the dry adiabatic lapse rate: dt g Ckm dz adiabatic c p This is the rate at which a parcel of air will cool as it is lifted without becoming saturated ( dry ) or exchanging energy with its surroundings ( adiabatic ). The heat capacity of dry air at constant pressure is c p = 1004 JK -1 kg -1. Combining the hydrostatic equation with the gas law and integrating over height gives The altimeter equation: gz z p( z) p0 exp p0 exp, RT H which gives the decrease in pressure with height in a column of air with average temperature T. The scale height H = g / (RT) 8 km for the lower atmosphere, and p 0 is the pressure at height z =0. Inverting the altimeter equation gives The hypsometric equation: RT p1 z 2 z1 ln, g p 2 which gives the difference in height ( thickness ) between two pressure levels. For small differences, this can be approximated by The thickness equation: RT p z g p Δz is the thickness of a layer and Δp is the pressure drop across the layer. 6

10 The Clausius-Clapeyron equation: 1 des e dt s L R T relates saturation vapour pressure (e s ) to temperature. L v = 2.47 x 10 6 Jkg -1 is the latent heat of vapourization for water and R v = 461 J kg -1 K -1 is the gas constant for water vapour. Integrating the Clausius-Clapeyron equation gives: e s ( T) 6.11exp T for e s in hpa as a function of temperature in Kelvin. Amongst other applications, this gives the curved saturation line on the SVP diagram. For actual vapour pressure e, the relative humidity is RH = 100 e / e s (T) and the dew point temperature T d is such that e = e s (T d ). The psychrometer equation: T w T A 1 p v 2 v [ e ( T s w ) e] Wet-bulb temperature T w is the temperature of a wet surface cooled by evaporation. The psychrometer constant A p depends on ventilation and pressure: A p = 0.66 hpa C -1 at 1000 hpa for a ventilated surface, and A p ~ 0.8 hpa C -1 for an unventilated wet-bulb thermometer in a Stevenson screen. Rearranging the psychrometer equation gives e e T ) A ( T T ), p s( w w which is the equation of the sloping lines on the SVP diagram. Specific humidity and mixing ratio: Specific humidity q and mixing ratio w are related by w q w 1 w Specific humidity q, vapour pressure e and air pressure p are related by e q p The Stefan-Boltzmann equation: 4 L T s gives the longwave radiation (Wm -2 ) emitted by a surface with emissivity (dimensionless) and temperature T s (Kelvin). Stefan-Boltzmann constant σ = Wm -2 K -4. Wien s displacement law: 2897 max T gives the wavelength for peak emission from a black body at Kelvin temperature T. 7

11 Table of Constants Acceleration due to gravity, g = 9.8 ms -2 Constant in Wien s displacement law = 2897 μm K = m K Rotation rate of the Earth, Ω = rad s -1 Gas constant for dry air, R = 287 J kg -1 K -1 Gas constant for water vapour, R v = 461 J kg -1 K -1 Latent heat of vapourization of water, L v = J kg -1 Latent heat of melting of ice, L f = J kg -1 Mean radius of the Earth = 6370 km Solar constant, S = 1370 Wm -2 Specific heat of air at constant pressure, c p = 1004 J kg -1 K -1 Speed of light, c = ms -1 Stefan-Boltzmann constant, σ = W m -2 K -4 Typical density of air at the Earth surface, ρ = 1.2 kg m -3 Conversion between C and K: 0 C = K Conversion between inches and mm: 1 in = 25 mm Conversion between feet and metres: 1 foot = m 1 mb = 100 Pa = 1 hpa A table of constants and a list of equations will be supplied in exams. 8

12 Interpreting weather charts (based on Met Office Fact Sheet 11: Weather charts consist of curved lines drawn on a geographical map in such a way as to indicate weather features. These features are best shown by charts of atmospheric pressure, which consist of isobars (lines joining points of equal sea-level pressure) drawn around depressions (or lows) and anticyclones (or highs). Other features on a weather chart include fronts, troughs and ridges. These are drawn to highlight the areas of most significant weather, but that does not mean that there is nothing of significance elsewhere on the chart. Figure 1: Isobars, weather systems and fronts on a weather chart. Low pressure or depression Depressions are areas of low pressure, usually with a well-defined centre, and are usually associated with frontal systems and unsettled weather. Winds blow in an anticlockwise direction around depressions in the northern hemisphere, and clockwise in the southern hemisphere. High pressure or anticyclone Anticyclones are areas of high pressure, whose centres are often less well defined than depressions, and are associated with quiet, settled weather. Winds blow in a clockwise direction around anticyclones in the northern hemisphere, and this is reversed in the southern hemisphere. Fronts Early weather charts consisted simply of station plots and isobars, with the weather being written as comments, like Rain, heavy at times. During the 1920s, a group of Scandinavian meteorologists, known collectively as the Bergen School, developed the concept of representing the atmosphere in terms of air masses. Since the air masses could be considered as being in conflict with each other, the term front was used to describe the boundary between them. Three types of front were identified which depend on the relative movement of the air masses. 9

13 Cold Front A cold front marks the leading edge of an advancing cold air mass. On a synoptic chart a cold front appear as a line with triangles. The direction in which the triangles point is the direction in which the front is moving. Warm Front A warm front marks the leading edge of an advancing warm air mass. On a synoptic chart a warm front appears as a line with semi-circles. The direction in which the semi-circles point is the direction in which the front is moving. Occlusion (or occluded front) Occlusions form when the cold front of a depression catches up with the warm front, lifting the warm air between the fronts into a narrow wedge above the surface. On a synoptic chart an occluded front appears as a line with a combination of triangles and semi-circles. The direction in which the symbols point is the direction in which the front is moving. Troughs Fronts describe thermal characteristics and also happen to be where there is significant precipitation, but precipitation is not confined to fronts. Drizzle in warm sectors or showers in cold air occur fairly randomly, but lines of more organized precipitation can develop; these are called troughs and are shown by lines on a synoptic chart. Frontogenesis Development or marked intensification of a cold or warm front Frontolysis Disappearance or marked weakening of a cold or warm front Relationship between isobars and wind Wind is a significant feature of the weather. A fine, sunny day with light winds can be very pleasant. Stronger winds can become inconvenient and, in extreme cases, winds can be powerful enough to cause widespread destruction. The wind can easily be assessed when looking at a weather map by remembering that: closer isobars mean stronger winds; the wind blows almost parallel to the isobars; in the northern hemisphere, the wind blows round a depression in an anticlockwise direction and around an anticyclone in a clockwise direction. In the southern hemisphere, the opposite is true; winds around anticyclones can sometimes be even stronger than indicated by the isobars; in warm air, the wind is relatively steady and tends to blow at about two-thirds the speed that the chart would suggest, though there are exceptions to this; in cold air, the wind is usually as strong as indicated by the isobars and can be very gusty. 10

14 Station plots Good quality observations are one of the basic 'tools of the trade' for weather forecasting. The weather conditions at each individual station for a given time can be represented on a surface chart by means of station plot. This means that information which would take up a lot of space if written on a chart can be displayed in a quick and easy to understand format. Figure 2 shows an example of a plotted chart. Figure 2: An example of a plotted chart The land station plot can represent all the elements reported by a station, which typically include: Air temperature Cloud amounts Dew-point temperature Cloud types Wind speed Cloud heights Wind direction Present weather Visibility Past weather Atmospheric pressure and three-hour tendency Traditionally station plots for manned observing sites are based around a central station circle. Automatic weather observations are increasingly replacing these and being plotted on weather charts. To differentiate between the two, automatic observations are plotted around a station triangle. Each element of the observation, with the exception of wind, is plotted in a fixed position around the station circle or triangle so that individual elements can be easily identified. The plotting positions and an example are given in Figure 3. 11

15 Total cloud amount Figure 3: Plotting positions and an example of a manual land station circle The total amount of the sky covered by cloud is expressed in oktas (eighths) and is plotted by the amount of shading within the station circle for manned observations or station triangle for automatic stations. The symbols used for manual and automatic observations are shown in Tables 1 and 2, respectively. Table 1: Symbols for recording manual cloud cover observations Table 2: Symbols for recording automatic cloud cover measurements 12

16 Wind speed and direction The surface wind direction is indicated on the station plot by a line in the direction that the wind is coming from. Direction is measured in degrees from true North. Therefore a wind direction of 180 is blowing from the south. The wind speed is given by the number of feathers on the arrow. Half feathers represent 5 knots whilst whole feathers indicate 10 knots. A wind speed of 50 knots is indicated by a triangle. Combinations of these can be used to report wind speed to the nearest 5 knots. The symbols used are given in Table 3. Table 3: Symbols for wind speed Gust speed Gust speeds are measured in knots and are plotted as whole knots preceded by the letter G. i.e. G35 indicates a gust of 35 knots. Gust speeds are normally only recorded if they exceed 25 knots. Air temperature Air temperature is plotted to the nearest whole degree Celsius, i.e. 23 would indicate 23 C Dew point temperature Dew point temperature is plotted to the nearest whole degree Celsius, i.e. 18 C. Pressure Pressure is recorded in hectopascals and tenths and the last three digits are plotted. Therefore hpa would be plotted as 031 and hpa would be plotted as

17 Present weather In total the Met Office has 100 codes for recording the current weather at the time of the observation. Different types of weather are represented using different weather symbols, a key to which can be found in Table 4. Table 4. Symbols for present weather (continued on next page) 14

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19 Past weather Simplified versions of the present weather symbols, shown in Table 5, are used to indicate weather in the time since the last observation. No symbol is plotted on the station circle if the past weather is recorded as codes 0, 1 or 2. Table 5. Past weather symbols. Pressure Tendency Pressure trend shows how the pressure has changed during the past three hours, i.e. rising or falling, and pressure tendency shows by how much it has changed. The tendency is given in tenths of a hectopascal, therefore '20' would indicate a change of two hpa in the last three hours. Pressure tendency is indicated by the symbols in Table 6. Table 6. Symbols for pressure tendency 16

20 Visibility Visibility, which is how far we can see, is given in coded format, in either meters or kilometres. Visibilities below five kilometres are recorded to the nearest 100 metres, whilst those above five kilometres are given to the nearest kilometre. Codes for visibilities of less than five kilometres Code Distance (km) Code Distance (km) Code Distance (km) 00 < Not Used Codes for visibilities of more than five kilometres Code Distance (km) Code Distance (km) Code Distance (km) >

21 Low cloud type symbols Medium cloud type symbols High cloud type symbols 18

22 Cloud height Cloud heights are measured in feet. The way these are plotted varies depending on whether the station is an automatic or manned observing site. Example Cloud heights for automatic stations Code Height in feet 00 < Cloud heights for manned stations ,000-1, ,000-2, ,000-4, ,000-6, ,500-7, ,000 or above / Cloud height unknown Type of observation: Manned Total cloud amount: 8 oktas Wind Speed: knots Wind direction: South-westerly Air temperature: 23 C Dew point temperature: 18 C Pressure: hpa Present weather: Continuous moderate rain Past weather: Rain Pressure tendency: Falling 0.5 hpa in past three hours Visibility: 6 km Low cloud type: Stratus Low cloud amount: 6 oktas Low cloud height: feet Medium cloud type: Altostratus High cloud type: Cirrus Gust speed: 45 knots 19

23 Cloud height can be estimated in several different ways: (i) if objects of known altitude are obscured by clouds (e.g., Arthurs Seat 250m or 830 ft; Pentland Hills are ~450m or 1500ft); (ii) a useful rule of thumb is Cloud base height (in meters) = 125 (T T d ); (iii) determine the lifting condensation level using a skew T-ln p chart. Visibility objects from JCMB Object Bearing Distance Code Refectory chimney m 01 Royal Observatory km 10 Commonwealth Pool km 20 Appleton Tower km 25 Edinburgh Castle km 33 Pentland Hills (Caerketten) km 50 Corstorphine Hill km 57 (Queen Mary s Mount) (110 ) (11.5 km) 61 Cockenzie power station km 64 Lufness Point km 78 Berwick Law km 80 Lomond Hills km 81 Bass Rock km 82 Ochil Hills km 83 May Island km 84 The Beaufort Wind Scale Force Description Speed (knots) 0 Calm smoke rises vertically 0 1 Light air direction of wind shown by smoke drift but not by wind vanes Light breeze wind felt on face; leaves rustle; ordinary wind vane moved by wind Gentle breeze leaves and small twigs in constant motion; wind extends light flag Moderate breeze raises dust and loose paper; small branches are moved Fresh breeze small trees in leaf begin to sway Strong breeze large branches in motion; umbrellas used with difficulty Moderate gale whole trees in motion; inconvenience felt when walking against wind 8 Fresh gale breaks twigs off trees Strong gale slight structural damage (chimney pots and slates removed) Whole gale trees uprooted Storm rarely experienced inland; widespread damage Hurricane

24 Cloud Identification and Classification Clouds contain large numbers (typically m -3 ) of very small drops (~ 20 m in diameter). Clouds are continuously in a process of evolution and therefore appear in an infinite variety of shapes and sizes. Nevertheless it is possible to define a limited number of characteristic types or genera, each with a Latin name and standard abbreviation, applicable all over the world. The names are based on five Latin words: cumulus (heap), stratus (sheet), cirrus (lock of hair), altus (high), nimbus (rain). Each genus is assigned to one of three height bands - low, medium and high - based on the height of the cloud base. Low-level clouds (0-2 km) Stratus (St) - grey, structureless, extensive sheet of cloud, but sometimes in ragged patches. Stratocumulus (Sc) - grey/whitish patch or sheet of cloud composed of rounded masses or rolls, usually having an apparent width of 5 o or more. Cumulus (Cu) - detached, dense clouds with sharp outlines, forming mounds or towers with flat bases. The clouds are brilliant white where lit by the sun. Cumulonimbus (Cb) - heavy and dark clouds of large vertical extent. Their tops are usually fibrous and spread out. Precipitation is often seen falling from their bases. Medium-level clouds (2-4, 7, 8 km in polar, mid-latitude and tropical regions) Altocumulus (Ac) - shallow sheet of cloud composed of rounded masses or rolls, having an apparent width generally in the range 1 to 5 o. Altostratus (As) - largely featureless, greyish sheet, usually thin enough to reveal sun at least vaguely, as through ground glass. No halo phenomena. Nimbostratus (Ns) - extensive sheet of diffuse, precipitating grey cloud, thick enough to blot out the sun. Often accompanied by ragged low cloud (stratus). The base of nimbostratus may be in the low-cloud range at times. High-level clouds (3-8 km polar, 5-14 km mid latitudes, 6-18 km tropical) Cirrus (Ci) - clouds composed of ice crystals, usually in delicate filaments. Cirrocumulus (Cc) - thin white patch or sheet of cloud with dappled or rippled appearance, often fibrous in places and having an apparent width generally less than 1 o. Cirrostratus (Cs) - largely transparent white sheet of cloud of fibrous or smooth appearance, generally producing halo phenomena. Genera may be supplemented by adding a description name called a species. Some common species are: Fractus (fra) - broken or ragged (applied to Cu and St). Lenticularis (len) elements shaped like a lens or almond (applied to Sc, Ac and Cc). 21

25 Calculations with the Saturation Vapour Pressure Diagram e.g. air temperature (T) 15 C and wet-bulb temperature (T w ) 11 C e sat e T d T w T e sat = 17 hpa e = 10 hpa RH = 100 (10/17) = 59% T d = 7 C 22

26 Lab 1: Weather observations Record your observations here and use the SVP diagram on the next page to calculate the humidity variables. (Do your values have the correct number of significant figures and do they have units?) Date and time: Air temperature: Max. temperature: Min. temperature: Wet-bulb temperature: Dew-point temperature: Vapour pressure: Relative humidity: Total cloud cover: Low level cloud cover: Low level cloud type(s): Middle level cloud type(s): High level cloud type(s): Cloud base height: Wind speed: Wind direction: Current weather: Past weather: Visibility: Pressure (measured in lab): Pressure (corrected to Mean Sea Level): Pressure tendency: For this week only, you also have to submit your results on-line; instructions for how to do this will be sent to your university . Please submit your results as soon as possible after you have attended your lab, and by 5pm on Friday 27 th September at the latest. It should only take 5-10 minutes. It is important to submit your results, as the data will be used as part of the mid-term exercise. If you have no values for a particular category, leave it blank. Don't worry if some of your values appear to be incorrect; just enter what you have recorded. 23

27 SVP diagram for humidity calculations Skew-T ln p diagram for predicting cloud base heights; you will learn how to use this in Lab 6 24

28 Lab 2: Plotting observations Decode these station plots Type of observation: Total cloud amount: Wind Speed and direction: Air and dew point temperatures: Pressure: Pressure tendency and trend: Present and past weather: Visibility: Low cloud type, amount and height: Medium cloud type: High cloud type: Gust speed: Type of observation: Total cloud amount: Wind Speed and direction: Air and dew point temperatures: Pressure: Pressure tendency and trend: Present and past weather: Visibility: Low cloud type, amount and height: Medium cloud type: High cloud type: Gust speed: 25

29 Type of observation: Total cloud amount: Wind Speed and direction: Air and dew point temperatures: Pressure: Pressure tendency and trend: Present and past weather: Visibility: Low cloud type, amount and height: Medium cloud type: High cloud type: Gust speed: Type of observation: Total cloud amount: Wind Speed and direction: Air and dew point temperatures: Pressure: Pressure tendency and trend: Present and past weather: Visibility: Low cloud type, amount and height: Medium cloud type: High cloud type: Gust speed: Plot station circles for these observations 26

30 Type of observation: Manual Total cloud amount: 7/8 Wind Speed and direction: 5 knots SW Air temperature: 13ºC Wet bulb temperature: 10ºC Pressure: hpa Pressure tendency and trend: 2 hpa, rising then steady Present and past weather: Continuous drizzle, drizzle in last 3 hours Visibility: 4 km Low cloud type, amount and height: 1/8 shallow cumulus at 1500 feet Medium cloud type: Dense altostratus High cloud type: Gust speed: Type of observation: Manual Total cloud amount: 8/8 Wind Speed and direction: Calm Air temperature: 12ºC Wet bulb temperature: 11ºC Pressure: hpa Pressure tendency and trend: 4 hpa, rising Present and past weather: Continuous rain, rain in last 3 hours Visibility: 7 km Low cloud type, amount and height: 8/8 stratus at 200 feet Medium cloud type: High cloud type: Gust speed: Type of observation: Automatic Total cloud amount: 8/8 Wind Speed and direction: 20 knots NW Air temperature: 13ºC Wet bulb temperature: 10ºC Pressure: hpa Pressure tendency and trend: 2.1 hpa, rising then steady Present and past weather: Continuous rain, more than 50% cloud cover in last 3 hours Visibility: 40 km Low cloud type, amount and height: 5/8 at 500 feet Medium cloud type: High cloud type: Gust speed: 27

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32 Lab 2 Observations Use this sheet and the SVP diagram on the next page to record and plot your observations from Lab 2. More observation sheets are available at the back of this book for practice. Date and time: Air temperature: Max. temperature: Min. temperature: Wet-bulb temperature: Dew-point temperature: Vapour pressure: Relative humidity: Total cloud cover: Low level cloud cover: Low level cloud type(s): Middle level cloud type(s): High level cloud type(s): Cloud base height: Wind speed: Wind direction: Current weather: Past weather: Visibility: Pressure (measured in lab): Pressure (corrected to Mean Sea Level): Pressure tendency: Station circle: 29

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34 UK surface observations at 11:00 on Sunday 30 September Pick a few to decode for practice. 31

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36 Lab 3: Wind chill The purpose of this experiment is to investigate the effect that wind and evaporation have on heat loss from an object. This is related to wind chill in humans and the measurement of wetbulb temperature. Wind chill is the apparent temperature, if the air were still, felt on the exposed human body due to a combination of air temperature and wind speed. Wind chill does not affect inanimate objects, only warm-bodied humans and animals. A recent version of a wind chill table was derived from extensive studies by the meteorological services of Canada and the U.S. and is appropriate for heat loss from an exposed human face, taking account of physiological changes which occur when a person is exposed to cold stress. The wind speed in this table is appropriate to face level rather than normal anemometer level of 10 metres (see the section Air Temperature and Human Comfort in Ahrens). WIND SPEED AIR TEMPERATURE ( C) (ms -1 ) calm What to do Frostbite in >> 30 min 10 min 5 min Spend a few minutes reading these notes in full before you start so you know what to do. Ask if you are confused. In this experiment we will look at the rate of heat loss from a metal cylinder in air at various wind speeds in order to investigate the cooling effect of wind. Get into groups of 2 or 3 people (we only have 10 fans to go around). First determine the air temperature (T air ) in the lab using the temperature probe. Use a ruler to measure the (inner) dimensions of the tube you are using, and calculate the volume of water it will hold. Fill the tube with water from the hot tap (it should be C). Insert the cork and thermocouple in the top, locating the tip of the thermocouple as close to the middle of the tube as possible. Make sure the outside of the tube is dry. Make sure that the water is well-mixed before you take a temperature measurement by quickly inverting the tube. With the fan OFF, observe the water temperature (T water ) at regular intervals (~30 seconds) as it cools towards room temperature. About 7-8 minutes of measurements should be sufficient. Plot a graph of how T water varies with time. 33

37 Now repeat the experimental procedure three more times, but with the fan switched on. Try to start from the same temperature and keep the tube at the same distance from the fan (about 50 cm). The three extra experiments are: Tube exposed to a low wind-speed (about 0.5 m s -1 ) Tube exposed to a high wind-speed (about 2 m s -1 ) Tube exposed to a high wind-speed and wrapped in a wet paper towel Plot your results on the same graph as the first experiment (use a different colour or symbol for each one). Calculate how the cooling rate ( C s -1 ) evolves in each experiment. Plot the cooling rate against time. Use your results to determine by what factor the cooling rate at low and high speeds exceeds that in still air. For specific heat capacity of water 4200 J kg -1 K -1 and density 1000 kg m -3, what is the cooling rate expressed in J s -1 (equal to Watts, W)? (You will need to use the volume of water to calculate this). Add another axis to the cooling rate graph that shows the cooling rate in Watts. Lastly, but most importantly, write down a physical explanation of the range of results. Notes and calculations Room temperature = (you should record this at least twice) Volume of tube = Conversion factor between C s -1 and Watts = Physical explanation of results: Attach any additional pages securely 34

38 Temperature variation with time Time Experiment 1 Experiment 2 Experiment 3 Experiment 4 35

39 Cooling rate with time Time Experiment 1 Experiment 2 Experiment 3 Experiment 4 36

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41 Lab 4: The passage of a cold front On Saturday 4 th October 2008 a cold front passed the UK sometime in the afternoon. Met Office surface pressure charts at 12 noon and 6 pm and station plots from 9 am until 8 pm on the 4 th of October are shown on the next two pages. Examine each of the 12 station plots and enter data values on five graphs for the following variables at Leuchars in Fife: a) surface pressure (to nearest hpa) b) air temperature ( C) c) wind direction (to nearest 45 ) d) wind speed (knots plot only the central value of the range) e) cloud amount (fraction of 8ths) and low, medium and high cloud types Then answer the following questions: Q1) At what time did the cold front pass over Leuchars (to the nearest hour)? What other station symbol (not one of the variables in the graphs) would enable you to determine that time? Q2) Describe the temperature change between the hour that the front passed and the hour after. Q3) At what other time of day was there a similar variation in temperature between two consecutive hours and how do you explain this? Q4) Describe the wind direction change between the hour that the front passed and the following hour. Did the wind veer or back? Is this to be expected? Q5) Describe the variation in wind speed in the hours proceeding, at the time of, and the hour following the passage of the cold front. Q6) At what time did the sky begin to clear (reduced cloud amount by 5/8 oktas or less) after the passing of the front? Q7) What other cloud types appeared when the overall cloud amount reduced substantially (to 1/8 oktas) and what might this suggest? 38

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45 Lab 5: Convection The atmosphere is, in general, notably stable with respect to the dry-adiabatic lapse-rate, but sunshine heats the Earth s surface and this heating is communicated upwards by turbulent convective motions in the atmospheric boundary layer. We can simulate this in the laboratory using a tank of water with a heating plate at its base. A stable stratification in the tank (increasing temperature with height) can be set up using an immersion heater and the temperature profile can be determined using thermistors. The motion of the fluid is made visible by introducing a potassium permanganate solution at the bottom of the tank. After switching on the heating, thermals will be seen to rise from the base, overshoot the level at which they have zero buoyancy (the level where the temperature of the thermal is equal to that in its surroundings) and sink back. Successive thermals rise higher as the warmed layer deepens. Preparation Heat the upper layer of the water carefully so as not to disturb the lower layers. Pour the potassium permanganate solution down the funnel carefully so that it spreads evenly across the bottom of the tank without mixing upwards. Note heights of thermometers above the base and initial temperature readings. Turn the heater dial to the voltage marked to give a 1 W cm -2 heat flux and start timing. Observations Take temperature readings every minute. When thermals start to rise, sketch their structure. Sketch convection cells viewed by looking down into the tank. Record temperatures and heights of the mixed layer as it develops; this will happen quickly, so take measurements more frequently. Switch off the heating as the mixed layer approaches a constant height. Note the structure of the layer top. Analysis Plot temperatures against thermometer height for at least the starting and finishing times on the same graph. Plot the depth of the mixed layer against time. Calculate the average surface heat flux from the area between initial and final temperature profiles using the equation c z H0 Ti t c is the volumetric heat capacity of water (4.2 J C -1 cm -3 ), δz is the distance between thermistors (2 cm), Δt is the time between the initial and final measurements (in seconds), ΔT i is the difference between initial and final temperatures for one thermistor, and Σ denotes the sum over all the thermistors. How well does your result compare with the expected 1 W cm -2? Why might they differ? 42

46 Temperature profiles Time Temp. 1 Temp. 2 Temp. 3 Temp. 4 Temp. 5 Plume height 43

47 Plume height / mixed layer depth with time Notes, calculations and sketches Attach any additional pages securely 44

48 Lab 6: The skew-t ln p diagram In this lab, we explore the make-up of the skew T ln p diagram, and use it to plot and analyze vertical temperature and dew point measurements. There are blank charts in this book, but extra copies will be handed out in the lab; make sure you stick/staple these securely into your lab book if you use them for plotting. You can also find a pdf of this chart to print off yourself on WebCT, or here: 1. First, let s try and identify what the different lines are on this complicated chart. On the first blank skew T ln p diagram: (a) Colour and label three isobars (lines of constant pressure, p): 1000, 500 and 200 hpa. (b) Using a different colour, label three isotherms (lines of constant temperature, T): -20, 0 and +20 C. (c) Similarly, label dry adiabats with potential temperatures (θ): -20, 0 and +20 C. (d) and wet adiabats with wet-bulb potential temperatures (θ w ): -20, 0 and +20 C. (e) Finally, label three lines of constant saturation mixing ratio (w s ) (1, 2, 5 g kg -1 ). 2. Now let s look at a set of measurements from Lerwick, Shetland, on 17 October 2009: Pressure (hpa) Temperature ( o C) Dew-point ( o C) (a) Plot these data on the second blank chart - both dew point (T d ) and temperature (T). Connect the points for each quantity with straight lines, ideally in different colours (if your lines cross, something went wrong: by definition T d must always be less than or equal to T). (b) What is the moisture content (or saturation mixing ratio, w s ) of the air at 930 hpa and 850 hpa? Estimate the range in moisture content of air near to the surface ( hpa) and compare this to the moisture content of air between hpa. Why do they differ? 45

49 (c) Describe the main features of the temperature profile (you should find four distinct height ranges which show different behaviours). What do each of these layers correspond to? Estimate the potential temperature (θ), and thickness (in metres) of air in the lowermost layer. (d) Replot the 1000 hpa points on the expanded diagram above (first label some pressures and heights on the vertical axis), and use Normand s Law to estimate the lifting condensation level. Lifting condensation level in hpa: In m: This level is approximately where rising surface air would condense and form a cloud. You can use this method to estimate cloud base height if you know T and T d. (e) Finally, use the enlarged diagram to determine the wet-bulb temperature at 1000 hpa. Wet-bulb temperature: 46

50 Chart for question 1 47

51 Chart for question 2(a) 48

52 Lab 7: Analysis of a typical thunderstorm in Edinburgh, 7 th June 2011 On 7 th June 2011, in mid-afternoon, I was looking out my office window and observed the sky blacken quickly; there was a sudden onset of torrential rain, then hail, accompanied by thunder. Shortly afterwards, the rain rapidly stopped. It was a typical example of a single cell thunderstorm. In this lab, we will take a look at some meteorological data gathered on that day, and try and understand what conditions led to this thunderstorm. The figure below shows measurements from the University of Edinburgh weather station (on the roof of JCMB), for ~24 hours from 0800 on 7 th June The first plot shows air temperature (from two different sensors in slightly different locations: one on the roof, one in the Stevenson screen); next shows rainfall amount (mm per 1 minute time interval); next shows solar flux; lowermost shows windspeed. Air temperature (black line WS sensor, grey line Stevenson screen) 1. Exactly (to the nearest ~5 minutes) when was the thunderstorm? Using the data above, quantitatively describe what happened over the hour or so before the storm, during the storm, and in the hour or so afterwards. 49

53 2. The table below shows temperature and dew-point data from a vertical sounding taken near Newcastle (the nearest available station to Edinburgh) at 12Z (closest to the time of the storm). Vertical sounding data from Albemarle (Northumberland) for 12Z 07 Jun 2011 Pressure, p (hpa) Temperature, T ( C) Dew-point, T d ( C) (a) Plot the data on a skew T-ln p chart (make sure you give the chart a sensible title, and clearly label the two curves). (b) Apply Normand s Law and graphically calculate the lifting condensation level (LCL) and the surface wet-bulb temperature (just like in the last lab). LCL (hpa) = T w = 50

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55 (c) Draw a saturated adiabat upwards from the LCL and shade the area of convective available potential energy (CAPE) this is an indication of the likelihood of a thunderstorm, as it identifies unstable air. You should find that this profile has some CAPE, suggesting that thunderstorms may occur. Indicate the equilibrium level (EL) on the chart and note it below (in both hpa and m). EL (hpa) = EL (m) = (d) Let us suppose that surface temperature increases above that seen in the profile (but that the rest of the profile stays the same), for example due to strong solar heating of the surface. Show on your chart what would happen to CAPE and the EL if the surface temperature increased to 20 C, and then 25 C. Estimate the increase in CAPE relative to the value from the observed profile for each of the higher temperatures. (e) Now go back and look at what happened to surface temperature during the Edinburgh storm. Again, estimate what happens to CAPE for the observed change in temperature. Why do think the storm was short-lived? 52

56 Lab 8: Radiation Instruments The purpose of this short lab session is to familiarise you with some radiation instruments and with the nature of solar and terrestrial radiation. Campbell-Stokes Sunshine Recorder This sunshine recorder has been used, and continues to be used, at many locations for measuring sunshine hours. It employs a glass sphere to focus the sun's rays to an intense spot, which will char a mark on a curved card mounted concentrically with the sphere. As the Earth rotates, the position of the spot moves across the card. When the sun is obscured, the trace is interrupted. At the end of the day the total length of the trace, less gaps, is proportional to the duration of sunshine. The record cards are made from a special card which produces a clearly visible trace even in weak sunlight. The cards are treated to char rather than burn to ensure clarity of the trace. Different cards are used for different seasons. Each card is marked with hourly intervals. We have one of these instruments for you to inspect. In the unlikely event that it is sunny, we may even be able to show it in action. Solarimeter surface. The solarimeter (or Moll-Gorczynski pyranometer) measures the intensity of solar radiation and gives a voltage output which can be measured with a multimeter. Use the solarimeter provided to measure the albedo of the surfaces provided. The albedo of a surface is the fraction (or percentage) of incident solar radiation that is reflected. We have one of these instruments available which will be set up as a demonstration, with two different surfaces at which it can be pointed. Record the downward and upward radiation readings for each surface in the table and calculate the albedo for each Surface Downward radiation Upward radiation Albedo Thermal Radiation primer In addition to the direct and scattered sunlight that surrounds us, we are also surrounded by a similar amount of radiation at much longer wavelengths. This is emitted by absolutely every object. The flux density, F, that leaves the surface of a body is given by Stefan's law: F = εσt 4, where T is the temperature of the body in KELVIN. The constant σ is a fundamental constant called the Stefan-Boltzmann constant: it has the value Wm -2 K -4. The emissivity ε is a property of the surface; it is a number lying between 0 and 1. A body whose emissivity is exactly 1 is called a perfect radiator or a black body. Note: To convert from Degrees Celsius to Kelvin, add

57 Radiation Thermometers We have three sorts of radiation thermometers: the large digitron instruments, a new pistol-style instrument and the small palm-ofthe-hand ones (see picture). All of these instruments receive thermal radiation from the object they are pointed at and display this as the temperature of a black body that would emit the same amount of radiation. The little instruments have a rather wide beam; the large ones (despite their clunky appearance) are better instruments for observing a small area from a large distance. The pistol-style instrument (if it is available) has an even narrower beam. Take a radiation thermometer and measure the radiative temperature of a variety of objects. Calculate the flux density that the object is emitting, and record the results below. Make sure that your test objects include the sky vertically above you and the roof of the building (or some other horizontal surface in the open air). What is the difference between the flux density leaving the roof and the flux density coming downwards from the sky? Make sure that one of your objects is a kettle of boiling water, which you know has a temperature of 100 C. We should have a kettle available with a black side and a polished metal side. Comment on the radiative temperatures that you observe from both sides: Surface Radiative temperature Flux density WARNING: The small radiation thermometers contain a laser pointer to help you aim the thermometer at a target. When using this BE VERY CAREFUL to ensure that you are not aiming anywhere near anyone else's eyes. NOTE: If your radiation thermometer seems to be giving odd results, check with one of your colleagues. If you are getting very different results, your instrument may have a flat battery, OR it may be set to assume an emissivity less than one. Ask a demonstrator for assistance. 54

58 Date and time: Air temperature: Max. temperature: Min. temperature: Wet-bulb temperature: Dew-point temperature: Vapour pressure: Relative humidity: Total cloud cover: Low level cloud cover: Low level cloud type(s): Middle level cloud type(s): High level cloud type(s): Cloud base height: Wind speed: Wind direction: Current weather: Past weather: Visibility: Pressure (measured in lab): Pressure (corrected to Mean Sea Level): Pressure tendency: Observation Sheet (extra blank copies) Station circle: 55

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60 Date and time: Air temperature: Max. temperature: Min. temperature: Wet-bulb temperature: Dew-point temperature: Vapour pressure: Relative humidity: Total cloud cover: Low level cloud cover: Low level cloud type(s): Middle level cloud type(s): High level cloud type(s): Cloud base height: Wind speed: Wind direction: Current weather: Past weather: Visibility: Pressure (measured in lab): Pressure (corrected to Mean Sea Level): Pressure tendency: Observation Sheet Station circle: 57

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62 Use of plagiarism detection software Note that computers may be used to detect plagiarism, whether by using something as simple as a search engine such as Google (it is as easy for a marker to find online sources as it is for you) or something more complex for specialized comparisons of work. Some courses will use the JISC plagiarism detection service. The plagiarism detection service is an online service hosted at that enables institutions and staff to carry out electronic comparison of students' work against electronic sources including other students' work. The service is managed by The University of Northumbria on behalf of the Joint Information Systems Committee (JISC) and is available to all UK tertiary education institutions by subscription. The plagiarism detection service works by executing searches of the world wide web and extensive databases of reference material, as well as content previously submitted by other users. Each new submission is compared with all the existing information. The software makes no decisions as to whether a student has plagiarised, it simply highlights sections of text that are duplicated in other sources. All work will continue to be reviewed by the course tutor. As such, the software is simply used as a tool to highlight any instance where there is a possibly case of plagiarism. Passages copied directly or very closely from existing sources will be identified by the software, and both the original and the potential copy will be displayed for the tutor to view. Where any direct quotations are relevant and appropriately referenced, the course tutor will be able to see this and will continue to consider the next highlighted case. Once work has been submitted to the system it becomes part of the ever growing database of material against which subsequent submissions are checked. The copyright in each work submitted remains with the original author, but a non-exclusive, nontransferable, licence is granted to permit use of the material for plagiarism detection purposes. There is an on-line demonstration of the system available at Own Work Declaration When you submit your work to the Teaching Office in Crew, please sign the Own Work Declaration form at the submission box to indicate that you have adhered to the University s policies. An example of what this form is on the next page. 59

63 OWN WORK DECLARATION By signing below, you indicate that you have adhered to the University of Edinburgh s Own Work Declaration I confirm that all this work is my own except where indicated, and that I have: 1. I have read and understood the Plagiarism Rules & Regulations in the course sections and Programme Handbooks; 2. I have clearly referenced / listed all sources as appropriate; 3. I have referenced and appropriately indicated all quoted text of more than three words (from books, web, etc); 4. I have given the sources of all pictures, data etc that are not my own; 5. I have not made any use of the essay(s) of any other student(s) either past or present; 6. I have not submitted for assessment work previously submitted for any other course, degree or qualification; 7. I have not incorporated any work from or used the help of any external professional agencies other than extracts from attributed sources; 8. I have acknowledged in appropriate places any help that I have received from others (e.g. fellow students, teachers in schools, external sources); 9. I have complied with any other plagiarism criteria specified in the course and Programme handbooks; 10. I understand that any false claim for any of the above will mean that the relevant piece of work will be penalised in accordance with the University regulations I understand that any false claim for this work will be penalised in accordance with the University regulations. Course Name [Course Code] Assignment Title Matric Number Name Signature Office Use s s s s s s s s s s s Last, First Last, First Last, First Last, First Last, First Last, First Last, First Last, First Last, First Last, First Last, First 60