MMM SEMINAR NCAR
The early formation of precipitation in cumulus was examined in STEPS (Colorado-Kansas, summer, 2000) with the S-Pol and CHILL radars. The objective was to obtain very early information, before and during the "first-echo" stage. (This means the first echo from precipitation, which is a matter for interpretation since one is already seeing echo from both insects and Bragg scattering). There is a conventional first echo from the formation of ice, which appears first near cloud top well above the freezing level and has no significant depolarization (zero ZDR). The new finding is that there also are millimeter and larger raindrops, both above and below the freezing level, at about the same or a slightly earlier time. This was not expected, and could well be an important factor in the microphysical evolution of these clouds. The positive ZDR that indicates the raindrops is at the upwind side of the updraft, and the conventional first echo is at the downwind side. It is not possible to determine from the radar data alone whether these drops originate by direct coalescence or by growth from recycled, melted ice at concentrations too low to be seen (though I prefer the latter explanation).
Thursday, August 19, 2004,
3:30 PM
Refreshments 3:15 PM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg 2 –Room 1022