Radia%on at the Top of the Atmosphere

Transcription

1 Radia%on at the Top of the Atmosphere Seiji Kato, Norman G. Loeb, Takmeng Wong, and Wenying Su NASA Langley Research Center

2 Outline of this talk Scien%fic ques%on How are TOA net radia%on and ocean hea%ng rate distributed in space and %me? CERES instruments Accuracy and stability EBAF-TOA data product ERBE data Addressing temporal distribu%on of net radia%on.

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5 CERES instruments CERES: Clouds and Earth s Radiant Energy System Broadband instruments Measure shortwave, longwave (total-sw), and window radiances in a cross-track mode Currently, CERES instruments are on Terra, Aqua and Suomi-NPP. Terra data start from March 2000 Aqua data start from July 2002 Suomi-NPP data start from Feb Footprint size of instruments on Terra and Aqua is ~20 km TOA irradiance stability is 0.3 Wm -2 per decade More information is on

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7 TOA irradiance uncertainty (1σ) Shortwave 5 1 Monthly Gridded (Wm -2 ) Global 3 (Wm -2 ) Longwave (day+night) : Terra only, prior to July : Terra+Aqua, July 2002 onwards 3: Annual and monthly Instrument calibra%on uncertainty is the largest component contribu%ng the overall uncertainty (Loeb et al. 2009)

8 CERES TOA irradiance stability Difference of the trend lines 0.02±0.3 Wm -2 per decade Meets the requirement of 0.3 Wm -2 per decade Loeb et al. 2007, J. Climate

9 EBAF-TOA Energy balanced (global TOA net irradiance agree with ocean hea%ng) Global net irradiance (SW+LW) is adjusted such that the July 2005 to 2010 mean net TOA irradiance is 0.58±0.38 Wm -2 (Loeb et al. 2012, the uncertainty at a 90% confidence level). 0.47±0.38 Wm -2 to a depth of 1800 m 0.07±0.05 Wm -2 below 2000 m 0.04±0.02 Wm -2 Ice warming and melt Clear-sky TOA irradiance is derived for partly cloudy footprints in addi%on to clear-sky footprints. Diurnal cycle of irradiance is included

10 Net TOA irradiance vs. ocean hea%ng Annual variability of ocean hea%ng agrees with TOA net variability Loeb et al. (2012)

11 History of ERBS Nonscanner Record ERBE nonscanner is one of the scientific instruments on the ERBS spacecraft ERBS was deployed and Launched on the Space Shuttle Challenger on 10/5/1984 Retired on 10/14/2005 after 21-year of service

12 Earth TOA radia%on measurements One month overlap with CERES instruments on Terra with the CERES instrument on TRMM is enough to calibrate longwave derived from ERBS nonscanner but not long enough to calibrate shortwave (need 2 to 3 years of overlap) If we can develop a correc%on algorithm to the %lt problem, ERBS nonscanner record can extend to August A Beeer calibra%on method that is consistent with CERES approach can be applied to ERBE data

13 Descrip%on of the ERBS Instrument Problem blockage tilt

14 Instrument Tilt Anomaly Ar%fact The effect of the instrument %lt anomaly, if not corrected, will appear as a sharp drop in the reflected shortwave fluxes aher 10/5/1999 Earth View ERBS pre = 92.2 (3.4) ERBS post = 76.5 (2.6) Before 10/5/1999 After 10/5/1999 (16 Wm -2 drop) ERBS Earth-viewing footprint with tilted sensor

15 20N to 20S Mean Reflected Shortwave Radia%on ERBS pre = 92.2 (3.4) ERBS nocor = 76.5 (2.6) ERBS cor = 92.8 (3.6) CERES = 93.1 (3.1) The revised algorithm moves the ERBS post-anomaly time series back to the same radiometric level as the pre-anomaly data The recovered ERBS nonscanner time series also matches well with the overlapping CERES SYN1deg data

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17 ERBE non-scanner calibra%on Wong et al. (2006)

18 Time dependent SW filter func%on SW filter func%on Dome Transmission Day α as a func%on of %me Day [ ] F(λ) = F 0 (λ) 1 β exp( αλ)

19 Monthly mean day%me minus nighlme LW irradiance

20 Using OHC measurements to constrain ERBE data Wong et al. (2006)

21 Use ocean hea%ng measurements to constrain TOA net Before 1993 Ocean hea%ng measurements + ocean reanalysis From 1993 through 2005 XBT with ocean al%meter Aher 2005 Argo

22 Issues and work need to be done ERBE ERBS only covers 60 S to 60 N Process NOAA 9 and NOAA 10 ERBE data (1985 to 1995) Use AVHRR and narrowband to broadband conversion to es%mate TOA broadband irradiances. Determine radia%on reference height Does not affect trand 20 km (CERES) vs. 30 km (ERBE) Pinatubo erup%on changes reference level

23 Summary CERES + ERBE data can provide TOA irradiances from Work with ocean community for the constrain Need more work to make ERBE ERBS data global

24 Back-ups

25 The Need to Monitor Earth s Energy Budget - Anthropogenic climate change is a perturba%on of the energy balance of Earth caused by changes in atmospheric concentra%ons of greenhouse gases and aerosol. - In response to a TOA radia%on imbalance, the Earth s energy flows are altered as the system adjusts to a new temperature. - Feedbacks in the system due to water vapor, clouds, atmospheric lapse rate, snow/ice act to counter or enhance the change in temperature. - It is thus cri%cal that we monitor changes in incoming and outgoing radia%on, clouds and aerosols as precisely as possible. 25

26 Tropical Mean Time Series: 2000C03 to 2002C05 ERBE vs. CERES, 36-day mean (Wm -2 ), 30NS ERBE - CERES, 36-day mean bias (Wm -2 ), 30NS Time mean bias = 0.1 Wm -2 The tropical (30NS) time series shows very good agreements between ERBS tilted nonscanner and CERES SYN1deg data The nonscanner data is a bit noisy with bias (ERBE-CERES) between -3 to 4 Wm-2 during the period. Time averaged bias ~ 0.1 Wm-2

27 Earth s Energy Budget (1σ Range) The radia%ve imbalance between the surface and atmosphere determines how much energy is available to drive the hydrological cycle and the exchange of sensible heat between the surface and atmosphere.