# Presentation: 353458

## Surface and TOA Cloud Forcing from the MLS IWC Product

- AURA Science Team Meeting:
- September 14, 2006
- Dan Feldman (Caltech)
- Jonathan Jiang (JPL)
- Hui Su (JPL)
- Frank Li (JPL)
- Yuk Yung (Caltech)

## Cloud Forcing Intro

- Clouds substantially impact on SW and LW radiative budget
- Substantial disagreement in cloud forcing (CF) in climate change scenarios
- Current understanding of UT cloud processes produces disagreements in vertical structure
- CF, if properly used, can diagnose the effect of clouds on climate sensitivity (Soden et al, 2004)
- What can the MLS IWC profiles tell us about the ice cloud contribution to cloud forcing?
- What lessons can be learned for application to CloudSat cloud forcing studies?

*Δ**TOA CRF from 2 x CO**2** for several GCM results Le Treut and McAveney, 2000*

- Introduction

*2006 Aura STM*

**Notes:**
In spite of these improvements, there has been no apparent narrowing of the uncertainty range associated with cloud feedbacks in current climate change simulations. A straight-forward approach of model validation is not sufficient to constrain the models efficiently and a more dedicated approach is needed. This should be favoured by a greater availability of satellite measurements.

## CF Calculation Basics

- Fast Correlated-K methods utilized
- RRTM_LW :
- Fluxes: ±1.0 W/m2 relative to LBLRTM
- Liquid, ice water clouds
- RRTM_SW :
- Fluxes: ±1.0 W/m2 direct, ±2.0 W/m2 diffuse
- DISORT: (4-stream w/δ-M scaling)
- Liquid, ice clouds + aerosols
- Fu-Liou:
- Shortwave flux from 2-stream
- Our calculation of CF:
- SW CF – LW CF > 0 → cooling
- SW CF – LW CF < 0 → heating

- Correlated-K Programs

*2006 Aura STM*

## CF Calculation Considerations

- Parameters relevant to cloud forcing calculations
- Cloud water path
- Effective particle diameter
- Habit distribution (for SW)
- Cloud fraction, overlap (for SW)
- T(z), H2O(z), O3(z)
- Appropriate spatial, temporal averaging
- Cloud water path and De are semi-independent quantities wrt remote sensing
- Cloud overlap approximation for non-unity horizontal grid cloud fraction
- Ad hoc schemes for estimating effective between-layer cloud fraction
- Morcrette et al. 2000: COA important
- Stephens et al. 2004: COA unimportant
- What to do about large MLS IWC product grid boxes?
- Temporal averaging
- For MLS, global coverage requires analysis at monthly time scales.

*Morcrette et al, 2000*

- CF Calculation Complications

*2006 Aura STM*

*Fu et al, 1996*

## MLS IWC Retrievals

- 200 x 7 x 3 km (along-track, cross-track, vertical)
- 118, 190, _**240**_, 640, and 2523 GHz frequencies utilized in retrieval
- <215 hPa, robust retrieval at 240 GHz
- Sequential nonlinear optimal estimation retrieval
- T, gas profiles first → clear-sky spectra
- Clear-sky – measurement → cloud-induced radiance
- CiR inverted for IWC
- Sensitivity range: 0.4 - 50 mg/m3
- Size distribution inferred from ambient T profile

*from Wu et al, 2006*

*from McFarquhar et al, 1997*

- MLS IWC Product

*2006 Aura STM*

## Validation Data: CERES

- CERES measures OSR, OLR, and cloud forcing aboard TRMM, TERRA, and AQUA
- Shortwave (0.3-5.0 μm)
- Total (0.3-50.0 μm)
- Window (8-12 μm)
- ES4 products:
- monthly gridded
- CERES/model hybrid data
- 2.5x2.5 resolution
- ERBE heritage
- ±6 W/m2 SW
- ±1.3 W/m2 LW
- Combination sets:
- Multiple CERES instruments
- MODIS L1B
- RAP & FAP modes

*From http://eosweb.larc.nasa.gov/*

*From http://lposun.larc.nasa.gov*

- CERES Products

*2006 Aura STM*

## MLS Standard + AIRS L3: 01/2005 vs. CERES

- CERES Intercomparison

*2006 Aura STM*

## LW Comparison with ECMWF calculations

- ECMWF Intercomparison

*2006 Aura STM*

## Validation Data: BSRN data

- SKYRAD:
- Diffuse, Direct SW Irradiance
- Downwelling LW Irradiance
- State-of-the-art instrument calibration validates cloud forcing calculations and satellite surface flux products
- Continuous sampling facilitates allows for validation of CF forcing calculation assumptions
- ARSCL active sounding information

*SKYRAD from www.arm.gov*

- Surface Site Description

*Map of surface stations from CAVE*

*2006 Aura STM*

## CERES surface flux prediction skill

*from http://www-cave.larc.nasa.gov*

- Surface Site Intercomparison

*2006 Aura STM*

## What about CloudSat (+ Calipso)?

- CLOUDSAT
- Radar activated 06/02/06
- Operational product specs: TOA, SRF flux ±10 W/m2 instantaneously
- L2 ATBD:
- Liquid De = 20 μm Ice De = 60 μm
- Will utilize Aqua MODIS to constrain cloud microphysical property parameters
- Deriving unbiased global cloud forcing maps from Cloudsat is non-trivial
- MLS still provides more global description of UT ice clouds than active sounders
- Ground-based validation more important than ever to interpret cloud forcing from liquid and ice clouds.

*Cloudsat’s quicklook at granule 01905, 9/6/06*
*(from http://cloudsat.atmos.colostate.edu)*

- CloudSat and Cloud Forcing

*2006 Aura STM*

## Conclusions

- Cloud forcing from MLS requires several assumptions:
- Cloud particle size
- Cloud overlap
- Unbiased temporal averaging
- As compared to CERES Aqua ES-4 product
- CF from MLS IWC spatial pattern agreement in tropics
- ECMWF IWC shows greater % of total CF
- Continuous surface site data indicate that:
- CERES LW surface forcing product robust
- CERES SW surface forcing product robust only in clear-sky scenarios
- Challenge for utilization of CERES, MLS (and Cloudsat + Calipso): ascription of cloud forcing to ice clouds

*2006 Aura STM*

## Acknowledgements

- The following individuals/groups have been invaluable for this work:
- Duane Waliser
- Baijun Tian
- Christopher Nankervis
- Eli Mlawer
- Yuk Yung’s IR Group
- NASA ESSF Program

*2006 Aura STM*

## References

- Radiative Transfer and Cloud Forcing:
- Fu, Q. and K. N. Liou (1992). "On the Correlated K-Distribution Method for Radiative-Transfer in Nonhomogeneous Atmospheres." _Journal of the Atmospheric Sciences_ **49**(22): 2139-2156.
- Fu, Q. A. (1996). "An accurate parameterization of the solar radiative properties of cirrus clouds for climate models." _Journal of Climate_ **9**(9): 2058-2082.
- Hu, Y. X. and K. Stamnes (1993). "An Accurate Parameterization of the Radiative Properties of Water Clouds Suitable for Use in Climate Models." _Journal of Climate_ **6**(4): 728-742.
- Mlawer, E. J., S. J. Taubman, et al. (1997). "Radiative transfer for inhomogeneous atmospheres: RRTM, a validated correlated-k model for the longwave." _Journal of Geophysical Research-Atmospheres_ **102**(D14): 16663-16682.
- Pincus, R., H. W. Barker, et al. (2003). "A fast, flexible, approximate technique for computing radiative transfer in inhomogeneous cloud fields." _Journal of Geophysical Research-Atmospheres_ **108**(D13).
- Hughes, N. A. and A. Henderson-sellers (1983). "The Effect of Spatial and Temporal Averaging on Sampling Strategies for Cloud Amount Data." _Bulletin of the American Meteorological Society_ **64**(3): 250-257.
- Morcrette, J.J. and C. Jacob (2000).  “The Response of the ECMWF Model to Changes in the Cloud Overlap Assumption.”  _Monthly Weather Review_ **128: **1707-1732.
- Stephens, G.L. et al. (2004) “An assessment of the parameterization of subgrid-scale cloud effects on radiative transfer. Part I: Vertical overlap.”  _Journal of the Atmospheric Sciences _**61 **(6): 715-732.
- Stephens, G. L., (2005), “Cloud feedbacks in the climate system: A critical review,” _Journal of Climate_, **18**, 237– 273.
- Soden, B. J. (2004) “On the Use of Cloud Forcing to Estimate Cloud Feedback” _Journal of Climate_, **17**, 3661-3665.
- Wu, D. L., (2006) “EOS MLS Cloud Ice Measurements and Cloudy-Sky Radiative Transfer Model” _IEEE Transactions on Geoscience and Remote Sensing_, **44** 1156-1165.
- McFarquhar, G. M. et al (1997) “Parameterization of the Tropical Cirrus Ice Crystal Size Distributions and Implications for Radiative Transfer” _JAS_, **34 **2187-2200.
- Le Treut, H. and B. McAvaney, 2000: Equilibrium climate change in response to a CO2 doubling: an intercomparison of AGCM simulations coupled to slab oceans. Technical Report, Institut Pierre Simon Laplace, **18**, 20 pp.
- IPCC TAR, Chapter 7 (_[http://www.grida.no/climate/ipcc_tar/wg1/260.htm](http://www.grida.no/climate/ipcc_tar/wg1/260.htm)_)
- AIRS L3 Data:
- AIRS V4 Data Release Description: (http://disc.gsfc.nasa.gov/AIRS/documentation/v4_docs/V4_Data_Release_UG.pdf)
- CERES Data:
- Wielicki, B.A.; Barkstrom, B.R.; Harrison, E.F.; Lee, R.B.; Smith, G.L.; Cooper, J.E. 1996: Clouds and the earth’s radiant energy system (CERES): An earth observing system experiment, _Bulletin of the American Meteorological Society _77 (5): 853.
- Loeb, N. G., K. Loukachine, et al. (2003). "Angular distribution models for top-of-atmosphere radiative flux estimation from the Clouds and the Earth's Radiant Energy System instrument on the Tropical Rainfall Measuring Mission satellite. Part II: Validation." _Journal of Applied Meteorology_ **42**(12): 1748-1769.
- Surface Data:
- CERES/ARM Validation Experiment: (_[http://www-cave.larc.nasa.gov/cave/cave2.0/Pubs.html](http://www-cave.larc.nasa.gov/cave/cave2.0/Pubs.html)_)
-  Long, C. N., T. P. Ackerman, Identification of clear skies from broadband pyranometer measurements and calculation of downwelling shortwave cloud effects, J. Geophys. Res., 105(D12), 15609-15626, 10.1029/2000JD900077, 2000.
- Heimo A., Vernez A. and Wasserfallen P. (1993) Baseline Surface Radiation Network (BSRN). Concept and Implementation of a BSRN Station. WMO/TD-No. 579, WCRP/WMO.
- CloudSat:
- Stephens, G. L., D. G. Vane, et al. (2002). "The cloudsat mission and the a-train - A new dimension of space-based observations of clouds and precipitation." _Bulletin of the American Meteorological Society_ **83**(12): 1771-1790.
- L’Ecuyer, T.S. CLOUDSAT L2 ATBD (2004)

*2006 Aura STM*