Abstracts
SEARCH Open Science Meeting
October 27, 2003
Seattle, Washington, USA
Using AVHRR Satellite Data to Investigate the Possible Effects of Dimethylsulfide Fluxes from a Coccolithophore Bloom on Regional Cloud Characteristics Over the SE Bering Sea
Bernard A. Walter1
1NorthWest Research Associates, P. O. Box 3027, Bellevue, WA, 98009, USA, Phone 425-644-9660 , Fax 425-644-8422, walter@nwra.com
Recent changes in the Bering Sea ecosystem have included large blooms of coccolithophores. Coccolithophores are known to produce significant quantities of dimethyl sulfide (DMS) which is released to the atmosphere. Atmospheric DMS oxidation products increase the number of cloud condensation nuclei (CCN) which can modify the droplet distributions in clouds resulting in larger numbers of smaller-sized droplets and changes in cloud reflectivity, cloud lifetime, and precipitation frequency. Increased DMS concentrations over the Bering Sea thus could have a significant impact on the ecosystem through changes in the cloud cover and the radiative fluxes.
We use the Cloud and Surface Parameter Retrieval (CASPR) software package (Key, 2002) to process 5 km AVHRR Polar Pathfinder (APP) data over the SE Bering Sea for the period April through October for the years 1993-2000 (covering pre- and post-coccolithophore bloom time periods). CASPR-derived variables include cloud and surface characteristics as well as short and long wave radiative fluxes at the surface and top of the atmosphere. Time series of variables obtained from CASPR including cloud effective droplet radius, channel 3 (3.7 mm) reflectance, cloud optical depth, columnar droplet concentration and albedo will be presented.
Preliminary analysis of plots of the trend in cloud effective droplet radius, Re, shows a decrease in the mean effective cloud droplet of 0.325 mm per year. The F-test showed that this trend is significant at the 95 % confidence level. The trend though begins at the beginning of the period being considered here not at 1997 when the coccolithophore bloom began. The mean value though of Re for 1993-1996 is 16.41 mm and that for 1997-2000 is 15.21 mm, a decrease of 7.3 %. A similar decrease in Re was also seen in clouds that had cloud top temperatures greater than 273 deg K (low-level liquid water clouds), but the decrease was not as large as that reported above. If our hypothesis is correct we would expect a decrease in Re from the increased number of CCN due to the large flux of DMS from the coccolithophore bloom.
A positive trend in the channel 3 reflectance is also observed. The increase over the period is about 3 % but the F-test showed that the trend was not significant. The trend though from 1995 to 2000 is highly significant and much larger. Future work will also include investigating the trends in the radiative fluxes.
Abstract Categories: Changes in the Atmosphere
Back to main abstract page
To view the list of records returned in your search you can use your browser's
back button, or perform the same search again:
| 