NEAR REAL-TIME VIEWS: GULF STREAM AND TROPICAL OCEANS

Transcription

1 COS 11-1 NEAR REAL-TIME VIEWS: GULF STREAM AND TROPICAL OCEANS 1. As directed by your instructor, complete this activity. Also print the Weekly Ocean News or Supplemental files as designated. (Check for additional News updates during the week.) 2. Reference: Chapter 11 in the Ocean Studies textbook. Complete the Investigations in the Ocean Studies Investigations Manual as directed by your instructor. Introduction: The AMS Ocean Studies Investigations Manual s Investigations 11A and 11B explore the close coupling of the ocean and atmosphere. The first examined was the Gulf Stream, followed by El Niño/La Niña. Here, we will visit recent views of the Gulf of Mexico/North Atlantic and tropical Pacific to update the current sea surface conditions. The Gulf Stream: The Ocean Studies einvestigation Manual Investigation 11A introduced the U.S. Naval Oceanographic Office s Gulf Stream maps. For a colorized animation of the Gulf Stream for the most recent past 12 months, go to It utilizes real-time 1/12 Global HYCOM Nowcast/Forecast System ocean model products to show the position and magnitude of sea surface temperatures (SST) that reveal the Gulf Stream. The animation displays numerous features over the period of a year, including broad expanses of high SST peaking in late summer to early fall to the east of Florida and other southeastern states, and the obvious direction of flow of the Gulf Stream, as well as rotating swirls of relatively warmer and cooler water marking locations of eddies. For a comparison of ocean conditions associated with the Gulf Stream at different times of the year, this Current Ocean Studies 11 Figure 1 displays information for 22 October 2014 (upper map) and 19 March 2016 (lower map). Among recent changes in the formatting of the Gulf Stream satellite analysis map by the U.S. Naval Oceanographic Office, the upper map shows SST in Celsius degrees while the more recent lower map shows SST in Fahrenheit degrees. Notice the differences in latitude and longitude intervals on the two maps. On both maps the thinly drawn curves mark water-mass boundaries. [The boundaries are labeled: GS for Gulf Stream, LC Loop Current, SG Sargasso Sea, SH Shelf Water, and SL Slope Water, and are combined with E, S, W, and N to identify eastern, southern, western, and northern boundary positions.]

2 Figure 1. Satellite analysis. Upper map 22 October Lower map 19 March 2016 [U.S. Naval Oceanographic Office] COS 11-2

3 COS Compare in the two Figure 1 maps the positions of the Gulf Stream (boundaries labeled GSN and GSS) east of mid-florida to the east of Cape Hatteras, NC. The positions were generally [(within two or three)(beyond five)] latitude/longitude degrees of each other. Note the close alignment of the Gulf Stream s northern boundary (GSN) on both maps from east of Florida to east of Cape Hatteras. This is primarily due to the physical barrier presented by the shallow continental shelf. 2. According to the SST values (in Celsius degrees) appearing on the upper map in the Gulf Stream segment east of mid-florida, the SST value on 22 October 2014 was 28 C, or 82.4 F. In Fahrenheit degrees, they were generally [(five degrees higher) (about the same)(four degrees lower)] compared to those on 19 March Intense tropical cyclones (e.g., hurricanes, typhoons) require broad expanses of ocean with SST of 26.5 C (80 F) or higher, among other requirements, to form. Examine Gulf of Mexico and Atlantic Ocean SST on the Figure 1 lower map for 19 March Based only on the temperatures shown on the map in those areas, you would expect that during early spring there is generally a [(low)(high)] probability of hurricane formation in the map area. 4. Examine the Figure 1 (upper) 22 October 2014 map. Based on the same minimum SST requirement, you would expect a [(lower)(higher)] probability of hurricane formation in the map area during mid-october than in early spring. We recommend that you track the Gulf Stream from time to time to see its changes. The latest Gulf Stream map similar to those used in this investigation can be found by going to the course website and at the bottom of the Physical & Chemical section, click on Additional Physical & Chemical Links. Then click on US Naval Oceanographic Office products. Scroll down to the SATELLITE ANALYSIS section and click on the buttons for Gulf of Mexico/Lower N. Atlantic Composite - b/w graphic (gif). You can also acquire color-coded version of this map at the location to confirm SST within cold and warm eddies. El Niño/La Niña: As described in the AMS Ocean Studies emanual Investigation 11B, the tropical Pacific Ocean is a coupled ocean-atmosphere system that has global scale impacts on weather and climate via the phenomena El Niño and La Niña. Figure 2 displays monthly average surface wind and temperature (SST) conditions across the tropical Pacific as acquired by the TAO/TRITON ocean buoy network for November Winds are reported as arrows with their tails at the observation location, their orientations showing direction, and their lengths showing relative speed. On the upper map, temperature isotherms are drawn with a 0.5 Celsius degree interval. The top map shows the warmest mean temperatures were centered at about 175 W, 5 S and the coolest at about 95 W and south of the equator.

4 COS 11-4 Figure 2. Mean surface wind and sea surface temperature conditions and anomalies from TAO/TRITON buoy array for the month of November The bottom map in Figure 2 displays mean sea-surface temperature and wind anomalies (departures from a long-term average) from about 95 W to 135 E and between about 10 S and 10 N. The temperature anomalies are color-coded with isotherms drawn at a 0.5 Celsius degree interval. The map shows that the broadest area of highest positive temperature anomalies in November 2015 centered on the equator at about [(100 W)(130 W)(170 W)(160 E)]. 6. During the same November 2015 time period, the lowest SST anomalies were located in the [(eastern)(central)(western)] tropical Pacific. The U.S., Canada, and Mexico have agreed to operational definitions of El Niño and La Niña. These definitions are based on three-month averages of SST anomalies (departures from normal) for a critical region of the equatorial Pacific Ocean (120 W to 170 W, 5 N to 5 S). Note these boundaries (or make a paper copy on which to mark the boundaries) on the Figure 2 bottom map which denotes anomalies (departures) in SST and winds from the longterm average. Positive anomaly isotherms are drawn as solid lines; negative anomaly isotherms are drawn as dashed lines. A positive SST departure from normal of 0.5 Celsius degree or greater for three consecutive months defines El Niño. A negative SST departure from normal of 0.5 Celsius degree or greater for three consecutive months defines La Niña. 7. Assuming that the SST anomalies within the boundaries you noted or marked on the Figure 2 bottom map are representative of a three-month average, the anomalies were consistent with a [(strong El Niño)(neutral)(strong La Niña)] episode. November 2015 was near the peak of the strongest episode described in Item 7 in recent years. Figure 3 presents tropical Pacific conditions for March Compare Figures 2 and

5 COS and note the considerable changes in the several months between November 2015 and March Figure 3. Mean surface wind and sea surface temperature conditions and anomalies from TAO/TRITON buoy array for the month of March Between November 2015 and March 2016, the tropical Pacific maximum monthly SST anomaly [(decreased about 1.0 C degree)(remained steady)(increased about 1.0 C degree)]. Summary: According to the 10 March 2016 EL NIÑO/SOUTHERN OSCILLATION (ENSO) DIAGNOSTIC DISCUSSION issued by NOAA s Climate Prediction Center, a strong El Niño was continuing through winter into spring 2016 although SST and other anomalies were weakening. The Discussion includes a prediction of a transition to neutral conditions during the late Northern Hemisphere spring or early summer 2016, with a close to 50% chance for La Niña conditions developing by fall There have been several significant El Niño and La Niña episodes in recent decades. An unusually intense El Niño developed rapidly in early 1997 and persisted until mid-may In late 1998, strong La Niña conditions were observed over the tropical Pacific and continued through The subsequent years experienced alternating neutral, weak or moderate El Niño and La Niña episodes. The current El Niño is the most recent to be classified as strong and has had significant impacts on weather and climate on the global scale. To keep up-to-date on conditions in the tropical Pacific, you can go to: For the latest 5-day and monthly average conditions from the TAO/TRITON array, go to and then click on one of the maps to see enlarged images depicting conditions across the tropical Pacific.

6 COS 11-6 If directed by your instructor, place the answers to Investigations 11A and 11B on the Investigations Answer Forms and this Current Ocean Studies on the Current Ocean Studies Answer Form linked from the AMS Ocean Studies RealTime Ocean Portal. Copyright 2016, American Meteorological Society