MMM SEMINAR NCAR
Observations
and Modeling Of Intense Hector Thunderstorms
Paul J. Connolly
UMIST, Manchester, ENGLAND
Island thunderstorms in the tropics often display the most intense development to be found anywhere on the globe. These storms affect climate in many different ways, one of which is through the formation of extensive cirrus layers that reside close to the Tropopause. This study is concerned with a thunderstorm known as Hector, which occurs almost daily during breaks from the monsoon over the Tiwi Islands, north of Darwin Australia. The strong development of Hector is related to the non-linear interactions of island sea breezes with the cold pools from early cumuli that form by mid-morning over the Tiwi Islands. In-situ observations of the cirrus-like outflow of Hector reveal that there are large concentrations of ice crystals in this region probably due to homogeneous nucleation of ice. The main tool used in this study is the U.K. Met. Office Large Eddy Model, which has been modified to include the effects of differential heating and surface roughness length over the Tiwi Islands. It has a parameterised microphysics scheme with 48 conversion rates between different hydrometeor species. The formation of the large ice crystal concentrations within the outflow of Hector is investigated by exploring the sensitivities of the microphysical properties of the outflow on various glaciation pathways in the Large Eddy Model. These sensitivity studies highlight the relative importance of each mechanism of glaciation on both the dynamical and microphysical properties of Hector. The effects of peninsula scale sea breezes are also considered as they have implications for parameterisation of convection at this geographical location. Finally, these results are confirmed by the use of the UMIST Explicit Microphysics Model.
Thursday, April 22, 2004,
3:30 PM
Refreshments 3:15 PM
NCAR-Foothills Laboratory
3450 Mitchell Lane
Bldg 2 –Room 1022