Evaluation of the fast visible RT model RTTOV-MFASIS and ... · Validation of ICON and ICON-LAM...
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RTTOV-MFASIS forward simulation SEVIRI 0.6 μm on Meteosat-11 and Meteosat-8 (IODC) 24 September 2018, 10 UTC Research and Development, Deutscher Wetterdienst, Offenbach, Germany [email protected] Christina Stumpf, Leonhard Scheck, Christina Koepken-Watts, Olaf Stiller, Liselotte Bach, Roland Potthast Evaluation of the fast visible RT model RTTOV-MFASIS and use for model cloud validation of ICON This work studies the fast RT method MFASIS for the simulation of visible satellite images available in RTTOV v12.2 and later versions. MFASIS is a lookup-table (LUT) based method. The LUTs are trained using the more accurate, 1D RT method RTTOV-DOM and are provided for SEVIRI, ABI and AHI via www.nwpsaf.eu. We evaluate RTTOV-MFASIS results for the visible SEVIRI channels based on global ICON model fields by comparing them to RTTOV-DOM results in a suitable test setup and to SEVIRI observations. These investigations pave the way for further updates to MFASIS and the validation of model cloud fields. First data assimilation experiments using MFASIS in convection-resolving models have demonstrated its value by improving the representation of cloud cover and precipitation . 3 Outlook Observation minus first guess (MFASIS) MFASIS forward simulation Observation RTTOV-MFASIS forward simulation under real viewing geometry and observation SEVIRI 0.6 μm on Meteosat-11, 24 September 2018, 12 UTC clear sky in model mean -0.020 stdev +0.176 rmse +0.178 sk +0.098 Comparison of first guess (RTTOV-MFASIS) and observation SEVIRI 0.6μm on METEOSAT-11, 24-30 September 2018, 9, 12, 15 UTC Contribution of different cloudy situations to MFASIS forward simulation Dependence of observation minus first guess (MFASIS) on sun zenith and scattering angle SEVIRI 0.6μm on METEOSAT-11, 24-30 September 2018, 9, 12, 15 UTC 12 UTC 9 UTC 15 UTC Simulated reflectance (left) shows similar cloud patterns as observation (middle) Largest errors occur where model cloud fields differ (right) Less cloud structure visible in model equivalent due to lacking 3D RT effects, e.g., due to cloud top inclination Correction for approximate cloud top inclination is planned for RTTOV v13 Overall shape of the observed reflectance is reproduced in model calculations (left) Observation minus first guess departures exhibit Gaussian shape, with clear-sky contributions promoting a peak in the mean (middle) Contributions from different atmospheric situations to reflectance histogram (right) 1 Comparison of simulated and observed reflectances Idea: Compare RTTOV-MFASIS forward simulations based on global ICON model fields to visible channel observations for the experimental period 24-30 September 2018 (hourly forecasts), offering a large variety of atmospheric situations and at different local times 2 Evaluation: RTTOV-MFASIS versus RTTOV-DOM Differences between reflectances from RTTOV-MFASIS and RTTOV-DOM simulations depend on viewing geometry and properties of the atmospheric profiles SEVIRI: Errors are typically larger for the 0.8μm channel Greenland profile: lat = 75, lon = -40 ICON elev. 3km RTTOV and libRadtran forward calculations for SEVIRI 0.6μm on METEOSAT-11, 3 July 2019, 12 UTC 2.1 Large MFASIS-DOM differences over Antarctica (winter) and Greenland (summer) Evaluate RTTOV-MFASIS forward operator in a test setup to identify systematic errors: Compare forward simulations using ICON model fields for 180.000 atmospheric profiles on a generic latitude-longitude grid with fixed satellite-sun viewing geometry to RTTOV-DOM results Differences (MFASIS-DOM) SEVIRI 0.6μm METEOSAT-11, 3 January 2019, 12 UTC no BRDF values (polar night) RTTOV v13 includes multiple Rayleigh scattering Currently: Flag regions of high terrain and large albedos Regions with high terrain and large albedo have large MFASIS-DOM differences because of missing multiple Rayleigh scattering processes in RTTOV-DOM (and in MFASIS LUTs) Errors significantly reduced in respective libRadtran- DISORT/-MFASIS calculations, which account for multiple scattering processes 2.4 Linear water-vapour correction Impact of water-vapour correction on differences (MFASIS-DOM) SEVIRI 0.8μm on METEOSAT-11, 3 January 2019, 12 UTC (60N - 60S) 2.2 Dependence of MFASIS-DOM differences on cloudy situations 2.3 Empirical mixed-phase cloud correction SEVIRI 0.6μm mean 0.005 stdev 0.010 rmse 0.011 sk 0.383 mean 0.003 stdev 0.018 rmse 0.018 sk -0.611 mean -0.001 stdev 0.011 rmse 0.011 sk -1.230 Comparison of first guess (RTTOV-MFASIS) and first guess (RTTOV-DOM) SEVIRI 0.6μm on METEOSAT-11, 3 January 2019, 12 UTC (60N - 60S) 20 40 60 80 100 120 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 Reflectance everything converted to water everything converted to ice ice fully above water (MFASIS) ice and water homogeneously mixed 100m water above ice 200m water above ice 500m water above ice 30 35 40 45 50 55 60 65 70 0.54 0.56 0.58 0.60 0.62 0.64 Reflectance Dependence of reflectance on scattering angle for idealised cloudy scenes: MFASIS WATER ONLY ICE ONLY HOMOG. MIX REALISTIC? Idealised scenes: SEVIRI 0.8μm channel is sensitive to water vapour in the atmosphere RTTOV v12.3 applies linear correction that accounts for cloud-top heights and water-vapour profiles not considered during LUT generation Introduce threshold on total ice and water optical depths to categorise model-field profiles to study reflectance differences obtained in RTTOV-MFASIS and RTTOV-DOM forward simulations and their dependence on atmospheric situations for different viewing geometries errors induced tails removed SEVIRI 0.6μm tails removed SEVIRI 0.8μm SEVIRI 0.6μm and 0.8μm on METEOSAT-11, 3 January 2019, 12 UTC (60N - 60S) Simple empirical mixed-phase cloud correction has overall neutral to slightly positive impact Work in progress to investigate improvements for mixed-phase cloud situations Errors in SEVIRI 0.8μm channel successfully reduced to same magnitude as other channels MFASIS assumes separate, homogeneous ice and water clouds at fixed height Ground-based and in-situ observations: realistic mixed-phase clouds can have a water-only layer on top of the ice-water composite Study idealised scenes to derive simple correction for mixed-phase clouds by using effective ice and water optical depths for the forward simulation Work in progress on evaluating RTTOV-MFASIS forward simulations against observations: Extend use of visible channel information to various imagers on board geostationary and polar orbiting satellites Use of level-2 products to analyse results and systematic errors classified by cloud types Future updates to RTTOV-MFASIS: Further improve mixed-phase cloud correction, approximation for cloud-top inclination, include multiple Rayleigh scattering processes Extend MFASIS to account for more RT effects and more particle species (aerosols) NNs Validation of ICON and ICON-LAM (limited-area version of ICON, in preparation) using visible channel information in conjunction with all-sky infrared simulations Assimilation of visible satellite observations in global and convection-resolving models Approx. linear dependence of first guess departures on sun zenith (left) bias correction? Larger errors expected in dependence of first guess departures on scattering angle in backscatter and cloud-bow region (right) To Do: Study effects of different cloud types and surface albedos; collect more statistics
Transcript of Evaluation of the fast visible RT model RTTOV-MFASIS and ... · Validation of ICON and ICON-LAM...
RTTOV-MFASIS forward simulationSEVIRI 0.6 μm on Meteosat-11 and Meteosat-8 (IODC)
24 September 2018, 10 UTC
Research and Development, Deutscher Wetterdienst, Offenbach, [email protected]
Christina Stumpf, Leonhard Scheck, Christina Koepken-Watts, Olaf Stiller, Liselotte Bach, Roland Potthast
Evaluation of the fast visible RT model RTTOV-MFASISand use for model cloud validation of ICON
MFASIS WATER ONLY ICE ONLY HOMOG. MIX
REALISTIC?
This work studies the fast RT method MFASIS for the simulation of visible satellite images available in RTTOV v12.2 and later versions. MFASIS is a lookup-table (LUT)based method. The LUTs are trained using the more accurate, 1D RT method RTTOV-DOM and are provided for SEVIRI, ABI and AHI via www.nwpsaf.eu. Weevaluate RTTOV-MFASIS results for the visible SEVIRI channels based on global ICON model fields by comparing them to RTTOV-DOM results in a suitable test setupand to SEVIRI observations. These investigations pave the way for further updates to MFASIS and the validation of model cloud fields. First data assimilationexperiments using MFASIS in convection-resolving models have demonstrated its value by improving the representation of cloud cover and precipitation.
3 Outlook
Observation minus first guess (MFASIS)MFASIS forward simulation Observation
RTTOV-MFASIS forward simulation under real viewing geometry and observation SEVIRI 0.6 μm on Meteosat-11, 24 September 2018, 12 UTC
clear sky in model
mean -0.020stdev +0.176rmse +0.178sk +0.098
Comparison of first guess (RTTOV-MFASIS) and observationSEVIRI 0.6μm on METEOSAT-11, 24-30 September 2018, 9, 12, 15 UTC
Contribution of different cloudysituations to MFASIS forward simulation
Dependence of observation minus first guess (MFASIS) on sun zenith and scattering angle SEVIRI 0.6μm on METEOSAT-11, 24-30 September 2018, 9, 12, 15 UTC
12 UTC 9 UTC 15 UTC
Simulated reflectance (left) shows similar cloud patterns as observation (middle)Largest errors occur where model cloud fields differ (right)Less cloud structure visible in model equivalent due to lacking 3D RT effects, e.g., due to cloud top inclination Correction for approximate cloud top inclination is planned for RTTOV v13
Overall shape of the observed reflectance is reproduced in model calculations (left)Observation minus first guess departures exhibit Gaussian shape, with clear-sky contributionspromoting a peak in the mean (middle)Contributions from different atmospheric situations to reflectance histogram (right)
1 Comparison of simulated and observed reflectancesIdea: Compare RTTOV-MFASIS forward simulations based on global ICON model fields to visiblechannel observations for the experimental period 24-30 September 2018 (hourly forecasts), offering a large variety of atmospheric situations and at different local times
2 Evaluation: RTTOV-MFASIS versus RTTOV-DOM
Differences between reflectances fromRTTOV-MFASIS and RTTOV-DOM simulationsdepend on viewing geometry and properties of theatmospheric profilesSEVIRI: Errors are typically larger for the 0.8μmchannel
Greenland profile:lat = 75, lon = -40
ICON elev. 3km
RTTOV and libRadtran forward calculationsfor SEVIRI 0.6μm on METEOSAT-11,
3 July 2019, 12 UTC
2.1 Large MFASIS-DOM differences over Antarctica (winter) and Greenland (summer)
Evaluate RTTOV-MFASIS forward operator in a test setup to identify systematic errors:Compare forward simulations using ICON model fields for 180.000 atmospheric profiles on ageneric latitude-longitude grid with fixed satellite-sun viewing geometry to RTTOV-DOM results
Differences (MFASIS-DOM)SEVIRI 0.6μm METEOSAT-11, 3 January 2019, 12 UTC
no BRDF values(polar night)
RTTOV v13 includes multiple Rayleigh scatteringCurrently: Flag regions of high terrain and large albedos
Regions with high terrain and large albedo have largeMFASIS-DOM differences because of missing multipleRayleigh scattering processes in RTTOV-DOM (and inMFASIS LUTs)Errors significantly reduced in respective libRadtran-DISORT/-MFASIS calculations, which account for multiplescattering processes
2.4 Linear water-vapour correction
Impact of water-vapour correction on differences (MFASIS-DOM)SEVIRI 0.8μm on METEOSAT-11, 3 January 2019, 12 UTC (60N - 60S)
2.2 Dependence of MFASIS-DOM differences on cloudy situations
2.3 Empirical mixed-phase cloud correction
SEVIRI 0.6μmSEVIRI 0.6μm
SEVIRI 0.8μm
Comparison of first guess (RTTOV-MFASIS) and first guess (RTTOV-DOM)SEVIRI 0.6μm and 0.8μm on METEOSAT 11, 3 January 2019, 12 UTC (60N-60S)
mean 0.005stdev 0.010rmse 0.011sk 0.383
mean 0.003stdev 0.018rmse 0.018sk -0.611
mean -0.001stdev 0.011rmse 0.011sk -1.230
Comparison of first guess (RTTOV-MFASIS) and first guess (RTTOV-DOM)SEVIRI 0.6μm on METEOSAT-11, 3 January 2019, 12 UTC (60N - 60S)
20 40 60 80 100 120
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
Refl
ecta
nce
everything converted to watereverything converted to ice
ice fully above water (MFASIS)
ice and water homogeneously mixed100m water above ice200m water above ice500m water above ice
30 35 40 45 50 55 60 65 70
0.54
0.56
0.58
0.60
0.62
0.64
Refl
ecta
nce
Dependence of reflectance on scattering angle for idealised cloudy scenes:
MFASIS WATER ONLY ICE ONLY HOMOG. MIX
REALISTIC?
Idealised scenes:
SEVIRI 0.8μm channel is sensitive to water vapour in the atmosphereRTTOV v12.3 applies linear correction that accounts for cloud-top heights and water-vapourprofiles not considered during LUT generation
Introduce threshold on total ice and water optical depths to categorise model-field profiles to study reflectance differences obtained in RTTOV-MFASIS and RTTOV-DOM forward simulationsand their dependence on atmospheric situations for different viewing geometries
errors induced tails removed
SEVIRI 0.6μm
tails removed
SEVIRI 0.8μm
SEVIRI 0.6μm and 0.8μm on METEOSAT-11, 3 January 2019, 12 UTC (60N - 60S) Simple empirical mixed-phasecloud correction has overallneutral to slightly positiveimpactWork in progress to investigateimprovements for mixed-phasecloud situations
Errors in SEVIRI 0.8μmchannel successfully reducedto same magnitude as otherchannels
MFASIS assumes separate, homogeneous ice and water clouds at fixed heightGround-based and in-situ observations: realistic mixed-phase clouds can have a water-onlylayer on top of the ice-water compositeStudy idealised scenes to derive simple correction for mixed-phase clouds by using effective iceand water optical depths for the forward simulation
Work in progress on evaluating RTTOV-MFASIS forward simulations against observations: Extend use of visible channel information to various imagers on board geostationary and polar orbiting satellites Use of level-2 products to analyse results and systematic errors classified by cloud typesFuture updates to RTTOV-MFASIS: Further improve mixed-phase cloud correction,approximation for cloud-top inclination, include multiple Rayleigh scattering processesExtend MFASIS to account for more RT effects and more particle species (aerosols) NNsValidation of ICON and ICON-LAM (limited-area version of ICON, in preparation) using visiblechannel information in conjunction with all-sky infrared simulationsAssimilation of visible satellite observations in global and convection-resolving models
Approx. linear dependence of first guess departures on sun zenith (left) bias correction? Larger errors expected in dependence of first guess departures on scattering angle inbackscatter and cloud-bow region (right) To Do: Study effects of different cloud types and surface albedos; collect more statistics
