The direct observations of large aerosol radiative forcing in the Himalayan region

[1] We show here that absorbing aerosols have led to a large reduction of surface solar radiation during winter over the Himalayan region. Our results are based on radiometric, aerosol and Lidar observations made at three sites in Nepal during winter 2003. The monthly mean aerosol optical depth (AOD) ranged from 0.2 to 0.34 and the TERRA satellite MODIS data reveal that AODs measured over these sites were typical of the entire Himalayan region. The near-surface aerosol single scattering albedo was in the range from 0.7 to 0.9. The presence of strongly absorbing aerosols resulted in a relatively large diurnal mean aerosol surface radiative forcing efficiency of −73 Wm−2 (per unit optical depth). The seasonal mean reduction in solar flux was as high as 25 Wm−2 and aerosol heating as much as 1 K per day within the first two kilometers.

[1]  Albert Ansmann,et al.  Vertical profiling of optical and physical particle properties over the tropical Indian Ocean with six‐wavelength lidar: 2. Case studies , 2001 .

[2]  Paul J. Crutzen,et al.  The Indian Ocean Experiment and the Asian Brown Cloud , 2002 .

[3]  Tami C. Bond,et al.  Calibration and Intercomparison of Filter-Based Measurements of Visible Light Absorption by Aerosols , 1999 .

[4]  P. Crutzen,et al.  Absorbing mediterranean aerosols lead to a large reduction in the solar radiation at the surface , 2002 .

[5]  V. Ramanathan,et al.  Aerosols, Climate, and the Hydrological Cycle , 2001, Science.

[6]  W. Conant.  An observational approach for determining aerosol surface radiative forcing: Results from the first field phase of INDOEX , 2000 .

[7]  Jonathan Williams,et al.  Vertical and horizontal distributions of the aerosol number concentration and size distribution over the northern Indian Ocean , 2001 .

[8]  J. Lelieveld,et al.  The Indian Ocean Experiment: Widespread Air Pollution from South and Southeast Asia , 2001, Science.

[9]  V. Ramanathan,et al.  Direct observations of aerosol radiative forcing over the tropical Indian Ocean during the January-F , 1998 .

[10]  O. Boucher,et al.  A satellite view of aerosols in the climate system , 2002, Nature.

[11]  S. Kinne,et al.  Aerosol-induced radiative flux changes off the United States mid-Atlantic coast: Comparison of values calculated from sunphotometer and in situ data with those measured by airborne pyranometer , 1999 .

[12]  V. Ramanathan,et al.  Aerosol modulation of atmospheric and surface solar heating over the tropical Indian Ocean , 2000 .

[13]  Alexander Smirnov,et al.  Ground-Based Lidar Measurements of Aerosols During ACE-2 Instrument Description, Results, and Comparisons with Other Ground-Based and Airborne Measurements , 2000 .

[14]  Patrick Minnis,et al.  Comparison of regional clear-sky albedos inferred from satellite-observations and model computations , 1986 .

[15]  Glenn E. Shaw,et al.  Indian Ocean Experiment: An integrated analysis of the climate forcing and effects of the great Indo-Asian haze , 2001 .

[16]  Carl L. Hubbs,et al.  SCRIPPS INSTITUTION OF OCEANOGRAPHY, UNIVERSITY OF CALIFORNIA , 1963 .

[17]  S. K. Satheesh,et al.  A model for the natural and anthropogenic aerosols over the tropical Indian Ocean derived from Indian Ocean Experiment data , 1999 .

[18]  James D. Spinhirne,et al.  Compact Eye Safe Lidar Systems , 1995 .

[19]  C. Flamant,et al.  Large‐scale advection of continental aerosols during INDOEX , 2001 .

[20]  Paul J. Crutzen,et al.  New Directions: Atmospheric Brown “Clouds”☆ , 2003 .

[21]  S. K. Satheesh,et al.  Large differences in tropical aerosol forcing at the top of the atmosphere and Earth's surface , 2000, Nature.