Properties of tropical convection observed by ARM millimeter-radars
| Haynes, John | Colorado State University |
| Stephens, Graeme | Colorado State University |
Category: Cloud Properties
The results of an analysis of tropical cloud systems observed from a variety of vertically pointing radar systems are described. In particular, observations taken during five years of operation of the ARM millimeter wavelength radar system (MMCR) at Manus Island in the Tropical West Pacific region are characterized into cloud classes according to the radar reflectivity structures of these cloud systems, associated rainfall, and surface radiative properties. These observations of cloud properties are composited with respect to various phases of the Madden Julian Oscillation, which is a dominant mode of variability at Manus Island. A method of better characterizing the attenuation of the radar signal at Ka-band in substantial in heavy rain is also introduced, using cloud boundary information collected from simultaneous geosynchronous satellite observations. In addition to the Manus study, observations of convection were collected from a ship-borne radar during the active phase of the monsoon in the Indian Ocean during the JASMINE experiment. It was found that the cloud and precipitation structures of different convective regimes are largely identical regardless of the mode of synoptic forcing. Instead, what varies is the frequency of occurrence of the different classes of cloud systems. Multi-layered cloud structures were associated with no less than 29 to 46% of the precipitating cases, and likely more than 50% after properly accounting for beam attenuation. This is, again, relatively independent of the mode of synoptic forcing. Approximately half of the accumulated surface precipitation fell from these multi-layered systems. In particular, the occurrence of rainfall from relatively shallow clouds overlayed by upper level cloud (i.e. cirrus or anvil) was found to be particularly prominent at Manus. Surface longwave fluxes vary modestly across the different types of convection, according to the water overburden. Fluxes vary by about 10 W m-2 between cloud classes and differ by about 20-30 W m-2 from the clear-sky. Solar transmittances reveal that about 50% less sunlight reaches the surface in precipitating regimes than under conditions of drizzle or cloud-only.
This poster will be displayed at the ARM Science Team Meeting.
