Evaluation of ECHAM5 General Circulation Model using ISCCP simulator

Evaluation of ECHAM5 General Circulation Model

using ISCCP simulator

Swati Gehlot & Johannes Quaas

Max-Planck-Institut für MeteorologieHamburg, Germany

2Outline • Motivation • Sub-column sampler • Results • Conclusion

Outline

• Background and motivation

• Model and data used

• Inclusion of sub-column sampler within the ISCCP simulator

• Results and discussion

• Conclusion

3

Motivation

• Global climate models work at a much coarser scale to resolve cloud processes and hence they are “parameterized”, leading to uncertainty

• In order to have confidence in the cloud parameterizations, the evaluation studies for GCM clouds are very essential

• ISCCP satellite data provides an adequately long time series for cloud climatology and microphysics

• This study focuses on application of ISCCP satellite simulator for detailed cloud diagnostics from ECHAM5 atmospheric GCM and model evaluation with comparison to observations

Outline • Motivation • Model • Sub-column sampler • Results • Conclusion

4

Model and data used

• Model evaluation studies for ECHAM5 GCM‐ Simulations with T63 spectral resolution‐ Additional module of ISCCP satellite simulator

• Analysis of diurnal cycle of convection using ECHAM5 data- Comparison of ISCCP-type cloud cover diagnosed in the model

with satellite data- Focus on high and convective clouds- Analysis of ISCCP histograms – model Vs observations

• Model verification studies using satellite data ‑ International Satellite Cloud Climatology Project (ISCCP) ‑ MODerate Resolution Imaging Spectroradiometer (MODIS)


5

ISCCP simulator

Additional module of ISCCP simulator is coupled with ECHAM5 to create ISCCP like cloud types in the model output

Low

Mid

High

ISCCP cloud types classification ISCCP cloud fraction histogram distribution


6

Need of a sub-column sampler

GCM Grid cell: 40-400km

Typical grid box in a GCM with inhomogeneous distribution of clouds within it

Figure from A Tompkins, ECMWF, 2005


7

Sub-grid scale variability: conventional approach

~50

0m

~200km grid box

Typical model grid box

(cloud overlap)


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Sub-column sampler

~50

0m

~200km grid boxDealing with horizontal cloud inhomogeneity and vertical overlap of clouds in the model grid box using stochastic cloud generator (based on Räisänen et al,

QJRMS 2004)

(Stochastically generated independent sub columns)


9

Case study over four tropical regions

2 1

3

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Area 1 – Africa 00oS to 30oS and 00oE to 30oEArea 2 – Amazon 00oS to 30oS and 25oW to 55oWArea 3 – India 00oN to 30oN and 60oE to 90oE Area 4 – Indonesia 10oN to 20oS and 90oE to 120oE


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Case study India: Diurnal cycle


Diurnal cycle for India: model, ISCCP data, and MODIS data

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Case study India: ISCCP histograms


Diurnal average ISCCP cloud fraction histograms: comparison of the model output, ISCCP data, and MODIS data

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Case study Africa: Diurnal cycle

Diurnal cycle for Africa: model, ISCCP data, and MODIS data


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Case study Africa: ISCCP histograms



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Global JJA averaged histograms (land and sea)



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Conclusion

• ECHAM5 model is evaluated using ISCCP simulator containing sub-grid variability information

• The model simulates the total cloud cover quite reasonably for the land and sea areas

• An overestimation of high and deep convective clouds is seen on comparison with ISCCP observations

• The model as well as ISCCP data miss a large amount of mid-cloud cover compared to MODIS observations

• Underestimation of low clouds in the model when compared to observations

• ISCCP and MODIS data show large discrepancies, particularly for land areas


16Outline • Motivation • Model • Sub-column sampler • Results • Conclusion

Thank you

Swati [email protected]

Max-Planck-Institut für MeteorologieHamburg, Germany

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Spare Sheets


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Geographical distribution of convective clouds


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Sub-grid cloud generator


Stochastic cloud generator for generating random sub-columns in a model grid cell

Initialized with GCM grid mean values of cloud fraction, liquid water and ice

Vertical variance by maximum-random cloud overlap assumption for cloud fraction and cloud condensate

Horizontal variance of total cloud water, using the Tompkins cloud scheme with beta distribution PDF

The generated sub-columns consist at each level of entirely clear sky, or entirely cloudy sky with constant cloud condensate

Tested with 100 sub columns, found reasonable global distributions of ISCCP variables.

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Case study Amazon: Diurnal cycle


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Case study Amazon: ISCCP histograms


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Case study Indonesia: Diurnal cycle


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Case study Indonesia: ISCCP histograms


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Summary: Diurnal cycle


Four tropical regions comprising of land and sea areas are analyzed for evaluation of diurnal cycle of ISCCP clouds (JJA04)

The amplitudes of diurnal cycle for model TCC varies between 5-17% (land) and 3-12% (sea) compared to ISCCP data TCC which lies between 10-13% (land) and 3-13% (sea). The land areas are slightly overestimated where as the sea areas are relatively well simulated by the model

For all the regions (land/sea), the high cloud cover (HCC) is overestimated in the model (8% in Africa to 43% in Indonesia)

The low cloud cover (LCC) is underestimated in the model in the range of 7% (in Amazon, fig 3) to 19% (in Indonesia, fig 5) compared to the ISCCP satellite observations.

The model underestimates the mid-cloud cover (MCC) with a range of 2% (in Africa, fig 3) to 10% (in Indonesia, fig 5) compared to the ISCCP satellite observations

The reasonable computation of ISCCP TCC is due to the cancellation of errors by the overestimation of HCC and the underestimation of LCC and MCC

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Summary: ISCCP histograms


For all the test areas, the model simulated ISCCP histograms were computed using diurnal average cloud amount for JJA 2004

The model diagnoses larger amount of high clouds (for eg. India), and the histograms reveal that these are optically very thin

The model misses much of the low cloud cover (LCC) and the mid-cloud cover (MCC), when histograms are compared with ISCCP observations

The globally averaged histograms show that the sea area is relatively well simulated in the model compared to the land area

The ISCCP simulator shows a decent agreement with the COSP simulator in terms of distribution of clouds in the ECHAM5 model

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Evaluation of ECHAM5 General Circulation Model using ISCCP simulator