A Possible Link of Aerosol and Cloud Radiations to Asian Summer Monsoon and Its Implication in Long

The influence of aerosol and cloud radiations upon the Asian summer monsoon was studied by using the global numerical weather prediction (NWP) model at the Japan Meteorological Agency (JMA). We parameterize both the direct and indirect effects of aerosols on radiative processes. In addition, criteria of cloud diagnosis are modified to enhance the cloud cover over the land in contrast to that over the ocean, considering that clouds form more easily over the land due to surface inhomogeneity and stay longer in the atmosphere due to smaller droplet size over the land than over the ocean. We confirm that the prediction of Asian monsoon activity is very sensitive to inclusions of aerosols and land-cloud enhancement. The control model, which uses the same cloud diagnosis scheme both over the land and over the ocean and does not include any effects of aerosols, systematically overpredicts the absorbed solar radiation (ASR) over land. The test model with these processes fairly reduces the systematic errors of land-ocean contrast of ASR. Over the Eurasian continent, the test model reduces ASR and lowers low-level temperature through land-atmosphere interactions. It suppresses monsoonal circulations in Southeast Asia and significantly delays northward migration of the typical fronts around East Asia, such as the Meiyu, Changma and Baiu fronts. The impact of land-cloud enhancement on one-month forecasts of the Asian monsoon seems to be similar to that of aerosols. Although the reduction of systematic errors of ASR indicates the relevance of the total effects of the two parameterization schemes, relative magnitudes of their impacts in nature are still uncertain. Further studies are required on distributions of aerosols and their optical properties, and cloud formation mechanisms particularly associated with the land-ocean difference, including aerosol-cloud interactions.

[1]  R. Pincus,et al.  Effect of precipitation on the albedo susceptibility of clouds in the marine boundary layer , 1994, Nature.

[2]  Andrew J. Heymsfield,et al.  Precipitation Development in Stratiform Ice Clouds: A Microphysical and Dynamical Study , 1977 .

[3]  Robert J. Charlson,et al.  Perturbation of the northern hemisphere radiative balance by backscattering from anthropogenic sulfate aerosols , 1991 .

[4]  S. Kreidenweis,et al.  Influence of sea-salt on aerosol radiative properties in the Southern Ocean marine boundary layer , 1998, Nature.

[5]  A. Slingo,et al.  General Circulation Model Calculations of the Direct Radiative Forcing by Anthropogenic Sulfate and Fossil-Fuel Soot Aerosol , 1997 .

[6]  Roger Davies,et al.  A fast radiation parameterization for atmospheric circulation models , 1987 .

[7]  J. Hansen,et al.  A parameterization for the absorption of solar radiation in the earth's atmosphere , 1974 .

[8]  Chengfeng Li,et al.  Seasonal Heating of the Tibetan Plateau and Its Effects on the Evolution of the Asian Summer Monsoon , 1992 .

[9]  J. Curry,et al.  A parameterization of ice cloud optical properties for climate models , 1992 .

[10]  F. Kasten.  Visibility forecast in the phase of pre-condensation , 1969 .

[11]  K. Liou,et al.  Influence of Cirrus Clouds on the Infrared Cooling Rate in the Troposphere and Lower Stratosphere , 1978 .

[12]  T. Krishnamurti,et al.  Numerical Simulation of the Somali Jet , 1976 .

[13]  B. Albrecht.  Aerosols, Cloud Microphysics, and Fractional Cloudiness , 1989, Science.

[14]  S. Tao,et al.  A review of recent research on the East Asian summer monsoon in China , 1987 .

[15]  Martin Wild,et al.  Validation of general circulation model radiative fluxes using surface observations , 1995 .

[16]  J. Kiehl,et al.  The Relative Roles of Sulfate Aerosols and Greenhouse Gases in Climate Forcing , 1993, Science.

[17]  B. Briegleb.  Delta‐Eddington approximation for solar radiation in the NCAR community climate model , 1992 .

[18]  S. Twomey.  The Influence of Pollution on the Shortwave Albedo of Clouds , 1977 .

[19]  J. Kristjánsson,et al.  Condensation and Cloud Parameterization Studies with a Mesoscale Numerical Weather Prediction Model , 1989 .

[20]  A. Arakawa,et al.  Interaction of a Cumulus Cloud Ensemble with the Large-Scale Environment, Part I , 1974 .

[21]  A. Lacis,et al.  Near-Global Survey of Effective Droplet Radii in Liquid Water Clouds Using ISCCP Data. , 1994 .

[22]  D. L. Roberts,et al.  A climate model study of indirect radiative forcing by anthropogenic sulphate aerosols , 1994, Nature.

[23]  T. L. Wolfe,et al.  An assessment of the impact of pollution on global cloud albedo , 1984 .

[24]  An Examination of the Clear-Sky Solar Absorption over the Central Equatorial Pacific: Observations versus Models , 1997 .

[25]  M. Sugi.  Description and performance of the JMA operational global spectral model(JMA-GSM88) , 1990 .

[26]  O. Boucher,et al.  General circulation model simulations of the Indian summer monsoon with increasing levels of sulphate aerosols , 1998 .

[27]  A. Slingo.  A GCM Parameterization for the Shortwave Radiative Properties of Water Clouds , 1989 .

[28]  M. Rodwell,et al.  A Model of the Asian Summer Monsoon. Part I: The Global Scale , 1995 .

[29]  Jun Matsumoto,et al.  Summer Monsoon over the Asian Continent and Western North Pacific , 1994 .