How To Understand Cloud Radiative Effects

Transcription

1 A Climatology of Surface Radiation, Cloud Cover, and Cloud Radiative Effects for the ARM Tropical Western Pacific Sites. Chuck Long, Casey Burleyson, Jennifer Comstock, Zhe Feng September 11, 2014 Presented at 2014 BSRN 13th Science and Review Workshop 1

2 Based on the paper: McFarlane, S. A., C. N. Long, and J. Flaherty, 2013: A Climatology of Surface Cloud Radiative Effects at the ARM Tropical Western Pacific Sites. J. Appl. Meteor. Climatol., 52, doi: D Plus continuing efforts. 2

3 ARM Tropical Western Pacific Sites Deep within the warm pool Late 1996 Eastern edge of warm pool Late 1998 Tropical summer monsoon Mid

4 Manus Monthly Averages 423 Wm Wm Wm Wm La Nina El Nino El Niño/La Nina periods based on the Oceanic Niño Index (ONI) determined by the NOAA Climate Prediction Center 4

5 Manus and Nauru Monthly Averages October 7, 2013 Nauru La Nina El Nino Manus La Nina El Nino (Manus/Nauru) Clr SWdn about same: (300/302) SWdn (205/237) SW CRE (-95/-65) Manus Tr Nauru >0.8 half the time, often associated with La Nina periods Clr LWdn about same (407/408) LWdn also about same (423/421) LW CRE small (15/12) 5

6 Darwin and Nauru Monthly Averages Darwin Dry Season May to Oct Nauru Darwin (Nauru) SWdn 234 (237) Clr SWdn 294 (302) SW CRE -60 (-65) Tr half time Similar to Nauru Tr half time Nauru only up to 0.9 LWdn 404 (421) Clr LWdn 392 (408) LW CRE 12 (12) La Nina El Nino October 7,

7 CRE by ENSO and Wet/Dry Manus: SW CRE only 4 Wm -2 and LW CRE only 3 Wm -2 difference EN to LN Nauru: SW CRE 53 Wm -2 difference, LW CRE only 6 Wm -2 difference EN to LN Darwin: SW CRE 69 Wm -2 difference, LW CRE only 8 Wm -2 difference Wet to Dry

8 Monthly Daylight Fractional Sky Cover Darwin Dry cloudiness 10-25%, Wet as cloudy as Manus Nauru El Nino cloudiness same as Manus, La Nina averages 35-50% October 7,

9 Relative Sky Cover Frequency: EN/LN, Wet/Dry Manus about same for EN and LN (less OVC, more clr) Less OVC for Nauru LN and Darwin Dry Darwin switches 35-40% OVC Wet for 40-45% Clr Dry Nauru has 2/3 time sky cover of 50% or less for LN Manus Nauru Darwin Solid: El Niño Dashed: La Niña 9

10 Analysis by Cloud Type: Classification Trimodal distribution (shallow, midlevel, and high clouds) Use Simple cloud classification from radar/lidar data product Notes: - Classification by cloud base, top, and thickness - Lower cloud class may include higher clouds radiative effects - Drizzle and rain are included as cloud thus stratiform with drizzle below freezing may be included in deep convection category 10

11 Cloud Type Example Manus, 7 November

12 Overall Occurrence by Cloud Type Manus Nauru Darwin Low and Cirrus 60% of occurrences 12

13 Bulk Cloud Radiative Effects (CRE) - Mean Cloud Radiative Effect (CRE) includes both frequency and individual cloud type effects - LW CRE dependent on cloud base height (temperature) -SW CRE dependent on cloud optical depth, primary driver of transmissivity signatures - Clouds with low bases (low, congestus, deep convection) contribute 71-75% of the surface SW CRE and 66-74% of the surface LW CRE at the three TWP sites 13

14 Ongoing research Extend the analyses including more recent data Will allow looking into EN/LN differences in cloud type distributions Extend these various analyses to diurnal cycle Aggregate, by ENSO/Monsoon, by cloud type Paper in preparation: Quantifying Diurnal Cloud Radiative Effects by Cloud Type in the Tropical Western Pacific. Casey D. Burleyson, Charles N. Long, and Jennifer Comstock. To be submitted to Journal of Applied Meteorology and Climatology October,

15 Diurnal Cycle of Cloud Type: Darwin Dry vs Wet Data spans Jan 2006 through May 2011 Dry Season May to Oct Wet Season Nov to April More frequent occurrence of all cloud types occurs during the wet season Evidence of transition to more frequent deep convection as well as anvil occurrence in the late afternoon into the night

16 Diurnal Cycle of Cloud Effect: Darwin Dry vs Wet Wet LW Dry LW Wet SW Dry SW Less cloudiness produces less SW and LW cloud effect for dry season than for wet Afternoon convection increase produces increased SW cloud effect in early afternoon

17 Diurnal Signature of CRE by Cloud Type Manus (a) Times (b) 17

18 Summary Manus, Nauru, and Darwin exhibit differing intraseasonal and interannual variability in the surface radiation budget, cloud amounts, and cloud distributions Due to differences in influence of climactic factors such as ENSO and the Australian monsoon Manus shows least variability, Darwin the most variability All three sites experience the same general cloud types Some differences in frequency of occurrence by type These basic cloud types exhibit similar cloud radiative effects No significant differences between sites for a given type Thus differences in the CRE are caused by differences in occurrence of cloud amount and mix of cloud type Simple classification by cloud base/top/thickness can separate optically different cloud types Thank You Chuck.Long@pnnl.gov 18