page 1© crown copyright simulation of radar reflectivities in the uk met office model: comparison...
TRANSCRIPT
© Crown copyright Page 1
Simulation of radar reflectivities in the UK Met Office model: comparison with
CloudSat Data
Alejandro Bodas-Salcedo, M.E. Brooks and M. Webb
GERB Science Team Meeting, Abingdon, 3 May 2007
© Crown copyright Page 2
Outline
• Introduction
• The A-Train and CloudSat
• Our approach
• Description of the simulator: subcomponents
• Global forecast model: comparison with observations
• Conclusions and future work
© Crown copyright Page 3
Relevance of clouds in the ARB
The vertical distribution and overlap of cloud layers determine the magnitude and vertical profile of radiative heating, which then exerts an influence in the large-scale circulation.
ATM Radiation Budget ATM CRFs
© Crown copyright Page 4
Impact on ocean heat transport
By modulating the distribution of heating between the atmosphere and the surface, clouds influence the circulation of the oceans.
(Glecker, GRL, 2005)
© Crown copyright Page 5
Feedback loop
These large-scale impacts are connected to cloud physical properties through a feedback loop.
(Stephens et al., BAMS, 2002)
This loop involves a wide range of spatio-temporal scales => the Unified Model appears to be an adequate framework to link interactions at different scales
© Crown copyright Page 6
A new perspective on clouds and the SARB
(http://cloudsat.atmos.colostate.edu/mission/formation_flying)
© Crown copyright Page 7
Synergy between active and passive sensing
(ESA SP-1257(1), 2001)
© Crown copyright Page 8
CloudSat
- Launch April 28th 2006. Operations began on June 2nd.
- Nadir pointing, 94GHz radar.
- 500m vertical resolution, oversampled at 240m.
- 1.4km x 2.5 km horizontal resolution
- Sensitivity ~-28 dBZ
- Dynamic range: 80 dBZ
- Calibration: 2 dBZ
© Crown copyright Page 9
Our approach
To facilitate the exploitation of CloudSat and CALIPSO data in numerical models, we are developing a system that allows to simulate the signal that CloudSat/CALIPSO would see in a model-generated world.
CFMIP CloudSat/CALIPSO Simulator (C3S):
LMD/IPSL, LLNL, CSU, UW, Met Office
Flexible tool to simulate active instruments in models (climate,
forecast, cloud-resolving) This 'model-to-satellite' approach has proven successful in recent
years, with the development of the ISCCP simulator1 and the simulation of satellite channel radiances2.
1: (Klein and Jakob, 1999; Webb et al., 2001)2: (Ringer et al., 2003)
© Crown copyright Page 10
Subcomponents
C3S MAIN SCOPS SG
PRECIPC3S SUB-GRID
CLOUDSAT CALIPSO SUMMARY STATISTICS
© Crown copyright Page 11
Case study I: analysis chart
• 2006/07/07 Transect trough a mature extra-tropical system
• Analysis chart valid at 18 UTC
• CloudSat overpass from 15:14:38 to 15:21:01
B
A
.
© Crown copyright Page 12
Case study I: MSG composite
RGB 321 (1.6 , 0.8 , 0.6 ) 1330 UTC: turquoise clouds contain ice crystals, whilst white clouds are water clouds (inc. fog). Vegetation creates a green signal and sandy areas are pink. Snow covered ground is turquoise.
B
A
© Crown copyright Page 13
Case study I: Ze
AB
1/120
1/55
© Crown copyright Page 14
Case study II: analysis chart
• 2006/12/09 Transect trough a mature extra-tropical system
• Analysis chart valid at 12 UTC
• CloudSat overpass from 14:57:10 to 15:03:53
A
B
© Crown copyright Page 15
Case study II: MSG composite
A
B
© Crown copyright Page 16
Case study II: Ze
AB
© Crown copyright Page 17
Case study III: analysis chart
• 2006/12/14 Transect trough a quasi-stationary front
• Analysis chart valid at 18 UTC
• CloudSat overpass from 15:12:36 to 15:15:53
A
B
© Crown copyright Page 18
Case study III: MSG composite
A
B
© Crown copyright Page 19
Case study III: Ze
AB
© Crown copyright Page 20
Cloud/Precipitation occurrence
© Crown copyright Page 21
North Atlantic statistics
© Crown copyright Page 22
Conclusions and future work
Tool to simulate radar reflectivities in the UM
New perspective on clouds and precipitation
Comparisons with global forecast model: The overall vertical structure of ML systems is well represented
LS precipitation is also generally well captured in the occluded sector
Cloud top height matches very well the obs.
Indications of too much cirrus/cirrostratus
Indications of too much drizzle production
Need to develop more quantitative, statistically-based approaches
Developing a community simulator: CFMIP CloudSat/CALIPSO Simulator (C3S) (LMD/IPSL, LLNL, CSU)
Flexible tool to simulate active instruments in models (climate, forecast,
cloud-resolving)
© Crown copyright Page 23