ANVIL CIRRUS OUTFLOW DURING THE MARITIME CONTINENT THUNDERSTORM EXPERIMENT
M.P.Jensen, T.P.Ackerman, E.E.Clothiaux, S.Sekelsky, R.McIntosh, W.Ecklund and K.Gage
The Experiment
The Maritime Continent Thunderstorm Experiment took place from 13 November to 10 December, on the Tiwi Islands , Austraalia. The primary objective of the experiment was to study the lifecycle of the thunderstorms which occur almost daily on these islands during the transition between wet and dry seasons. As part of this experiment, a suite of remote sensing instruments including a dual-wavelength millimeter radar, a 10cm vertically pointing radar, a microwave radiometer, a lidar and broad-band solar and IR radiometers (See figure below) were deployed at the village of Garden Point located on the Northwest corner of the Tiwi Islands (11.4S, 130.41E). Soundings were acquired at Maxwell Creek and a scanning Doppler radar was operated at Nguiu.
at a height of 12 to 15 km (see Ka-radar image below). A few hours later, the radar shows a lower but thicker cirrus layer extending from 6 to 13 km lasting until 1230 UTC. The Xs in the radar image represent the equivalent height of the GMS satellite derived IR brightness temperatures.
As the cirrus anvil moved over the site, the solar radiation signal dropped from 900 to about 150 W/m^2 (0530 UTC).
Optical Depth
In order to estimate an optical depth for the cirrus anvil, the vertical-average Ka-band radar reflectivity was determined. This average reflectivity was converted into an ice water content using Sassen's (1987) relationship. A specific extinction of 0.04 m^2/g (Kinne et al. (1992), Ackerman et al.(1988)) was used. The optical depth of the cirrus layer was found to vary between 110 and 20 between 0700 and 0800 UTC. Heating rate profiles for an optical depth of 100 were calculated.
Conclusions
Preliminary analysis of MCTEX anvil case study events shows high ice water paths and large optical depths. These anvils, therefore, have significant impacts on the radiation budget of the surface and upper troposphere. Model calculations show cloud-top IR cooling rates on the order of 24-27 K/day, cloud-top solar heating of 19-48 K/day and cloud-base IR heating of 14-19 K/day, averaged for layers with depth of 1km.
Future Work
The MCTEX dataset lends itself to more case study analyses of cirrus anvils. We have identified at least 2 more well documented anvil events. Several interesting phenomenological studies, for example anvil gravity waves, will also be pursued. In addition, we will coordinate these measurements with data from a scanning Doppler radar located about 50 km south of the Garden Point site at Nguiu.
As the cirrus anvil moved over the site, the solar radiation signal dropped from 900 to about 150 W/m^2 (0530 UTC).
