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Climate Science Branch, Science Directorate NASA Langley Research Center Shashi K. Gupta, Paul W. Stackhouse Jr.*, Taiping Zhang, and J. Colleen Mikovitz.

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Presentation on theme: "Climate Science Branch, Science Directorate NASA Langley Research Center Shashi K. Gupta, Paul W. Stackhouse Jr.*, Taiping Zhang, and J. Colleen Mikovitz."— Presentation transcript:

1 Climate Science Branch, Science Directorate NASA Langley Research Center Shashi K. Gupta, Paul W. Stackhouse Jr.*, Taiping Zhang, and J. Colleen Mikovitz Climate Science Branch, Science Directorate NASA Langley Research Center (LaRC) Hampton, Virginia *PI: NASA/GEWEX Surface Radiation Budget (SRB) Project Computation of Surface Longwave Fluxes Effect of Skin-Air Temperature Differences LANDFLUX Assessment and Organization Workshop Toulouse, France 28-31 May 2007

2 Climate Science Branch, Science Directorate NASA Langley Research Center The NASA/GEWEX SRB Dataset A 22-year (Jul1983-Jun2005) dataset produced at LaRC Monthly, Daily, Monthly/3-Hourly, and 3-Hourly at 1°x1° Algorithms: Primary and Quality-Check - SW and LW Input Data: Cloud Properties Derived from ISCCP-DX Meteorological Profiles from GEOS-4 Column Ozone: TOMS and TOVS Archives Validation Data: BSRN, WRDC, and GEBA Archives Submitted to GEWEX Radiative Flux Assessment Dataset and ancillary information will be available at: http://eosweb.larc.nasa.gov/PRODOCS/srb/table_srb.html

3 Climate Science Branch, Science Directorate NASA Langley Research Center 22-Year Average Surface Radiative Fluxes PR QC SWLW

4 Climate Science Branch, Science Directorate NASA Langley Research Center Multi-Year Global Averages * Normalized to S 0 = 1367 W m -2 ; (F 0 = S 0 /4) Parameter Ohmura & Gilgen (1993) GEBA Surf. Obs. Kiehl and Trenberth (1997) ERBE/ CCM3 Zhang & Rossow (2004) 21-Year Mean (1984-2004) NASA/GEWEX SRB Release 2.5/2.81* (NASA LaRC) 22-Year Mean (July 1983 - June 2005) SW, LWSW, LW QC Flux% F 0 Flux% F 0 Flux% F 0 Flux% F 0 Flux% F 0 SW Down169.049.419857.9189.255.4186.454.5183.753.8 SW Net142.041.616849.2165.948.5165.648.5161.047.1 LW Down345100.932494.8343.8100.6343.1100.4348.7102.0 LW Net-40.0-11.7-66-19.3-49.6-14.5-53.0-15.5-50.0-14.6 Total Net102.029.810229.8116.334.0112.632.9111.032.5 SW CRF-- -53.0-15.5-56.2-16.4-59.2-17.3 LW CRF-- 4613.529.58.635.310.334.310.0 Total CRF-- -23.5-6.9-20.9-6.1-24.9-7.3

5 Climate Science Branch, Science Directorate NASA Langley Research Center Introduction SRB Longwave Algorithms: 1.GEWEX LW (Fu/Stackhouse): CERES 2/4-Stream LW model (Fu et al., 1997), maximum-random cloud overlap, CERES spectral surface emissivity. Results: TOA and Surface, 3-Hourly, Daily, Monthly/3-Hourly, and Monthly data products. 2.GEWEX LW QC (Gupta et al., 1989, 1992): RT based parameterizations for clear/cloudy downward LW fluxes, CERES broadband surface emissivity. Results: Surface 3-Hourly, Daily, Monthly/3-Hourly, and Monthly data products. Both models overestimate DLF for some regions at the high end of DLF range. Determine the cause, assess the magnitude, and develop a remedy for this overestimation.

6 Climate Science Branch, Science Directorate NASA Langley Research Center Comparison of 3-Hourly Fluxes With BSRN Data PrimaryQuality-Check Investigate the cause focussing on the quality-check model

7 Climate Science Branch, Science Directorate NASA Langley Research Center WHAT IS CAUSING IT AND WHERE? Effective Emitting Temperature: T eff = 0.60 T s + 0.35 T 1 + 0.05 T 2 T s - Surface skin temperature T 1 - Average temperature for Sfc. - 800 mb layer T 2 - Average temperature for 800 - 680 mb layer Works well when T s, T 1, and T 2 conform to nominal lapse rate requirements. When T s >> T 1 (and T 2 ), it results in overestimation of DLF. Mostly over dry/arid regions during hot times of day.

8 Climate Science Branch, Science Directorate NASA Langley Research Center Weighting Function for DLF Reaching the Surface (U.S. Standard Atmosphere - 50 mb Layers)

9 Climate Science Branch, Science Directorate NASA Langley Research Center Methodology Selected two sites for study: Alice Springs, Australia - Dry/Arid Goodwin Creek, MS (USA) - Moderate/Humid Performed flux computations using a stand-alone version of the quality-check model on a 3-hourly time resolution for all months of 2000. Compared model-derived DLF with ground-based observations for the above sites obtained from BSRN.

10 Climate Science Branch, Science Directorate NASA Langley Research Center Analysis of Alice Springs Overestimation Points with overestimation of > 100 Wm -2 32 points during the year (16 in Jan; 20 in DJF) Mean = 120 Wm -2 ; Range: 100-160 Wm -2 T s : Mean = 324.3 K; Range: 302-336 K P s : Mean = 939 mb; Range: 935-946 mb T 800 : Mean = 292.1 K; Range: 284.7-297.7 K T s - T 800 : Mean = 32.2 K; Range: 17.0-40.3 K T s - T 800 should be about 10 K, but no more than 15 K Decided that lapse rates > 10K/100mb in the lower layer are too steep, and need to be adjusted. Adjusted skin temperature to not exceed 10K/100mb limit.

11 Climate Science Branch, Science Directorate NASA Langley Research Center Results From the Modified Computation Alice SpringsGoodwin Creek Bias for Alice Springs - reduced greatly; Change for Goodwin Creek - minimal

12 Climate Science Branch, Science Directorate NASA Langley Research Center Monthly Temperature Adjustment and Frequency Temperature AdjustmentAdjustment Frequency Jan Jul

13 Climate Science Branch, Science Directorate NASA Langley Research Center Model-Derived vs. Ground-Measured BSRN DLF (Primary Model) Alice Springs Goodwin Creek Alice Springs: Slight overestimation at the high end; small negative bias overall.

14 Climate Science Branch, Science Directorate NASA Langley Research Center Model-Derived vs. Ground-Measured DLF (Primary Model) Alice Springs Some overestimation at the high end during DJF; underestimation during JJA

15 Climate Science Branch, Science Directorate NASA Langley Research Center Summary and Future Work Determined the cause of DLF overestimation: Occurs when skin temperature (T s ) is much higher than atmospheric temperatures. Instantaneous overestimation can be 100 Wm -2 or even more. Developed a method for detecting this condition and constraining T s prior to using it in DLF computation, largely eliminating the bias. Constrained T s is not used for upward flux computation. Tested method with quality-check model for all months of 2000. Similar analysis is underway for the primary LW algorithm. Results of analysis to be applied in the next round of processing.

16 Climate Science Branch, Science Directorate NASA Langley Research Center Back-up Slides

17 Climate Science Branch, Science Directorate NASA Langley Research Center Model-Derived vs. Ground-Measured BSRN DLF (Quality-Check Model) Alice Springs Goodwin Creek Significant overestimation over Alice Springs; almost none over Goodwin Creek

18 Climate Science Branch, Science Directorate NASA Langley Research Center Model-Derived vs. Ground-Measured DLF (Quality-Check Model) Alice Springs Severe overestimation during DJF; slight underestimation during JJA

19 Climate Science Branch, Science Directorate NASA Langley Research Center Comparison of Daily Averages With BSRN Data PrimaryQuality-Check Overestimation not so apparent after diurnal averaging

20 Climate Science Branch, Science Directorate NASA Langley Research Center Monthly Temperature Adjustment and Frequency

21 Climate Science Branch, Science Directorate NASA Langley Research Center Surface and Atmospheric Temperatures Over Sea of Japan - January 2000

22 Climate Science Branch, Science Directorate NASA Langley Research Center Surface Skin Temperature From Different Datasets Jan2000Jul2000 GEOS-4 ISCCP Primary LW

23 Climate Science Branch, Science Directorate NASA Langley Research Center Surface Skin Temperatures From Different Datasets

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