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A Study of Ice − Phase Microphysics in Trmm − Lba Deep Convective Clouds
| Content Provider | Semantic Scholar |
|---|---|
| Author | Oliveira, José Carlos Parente De Filho, Múcio Costa Campos Costa, Alexandre Araújo |
| Copyright Year | 2002 |
| Abstract | Although the sun is the ultimate source of energy for the motions in the Earth’s atmosphere, most of this energy has to be first processed by convection to become available to the atmospheric circulations. In fact, it is recognized that the latent heat released in clouds, especially the convective clouds over the tropics drives atmospheric motions from local to global scales. In tropical regions, the atmospheric thermodynamics is mostly ruled by deep convective action. In opposition to surface processes and shallow convection, deep convective clouds produce a net latent heating through the depth of the troposphere, as they transport energy upward. Deep convection serves as a bridge that connects the free atmosphere and the boundary layer as well. Although in a large scale perspective deep convection can be seen in a state of quasi−equilibrium with a large− scale, destabilizing forcing (Arakawa and Schubert 1974), multiple scales are important to shape the characteristics of convection. This includes forcings on the mesoscale, cloud−scale circulations, turbulence and, on the extreme, microphysical processes. As pointed out by Emanuel (1994), the effect of cumulus convection on the redistribution of the water vapor in the atmosphere strongly depends on the detrained water substance and, therefore, is very sensitive to the cloud microstructure. In fact, it is at the scale of microphysical processes that the latent heat associated with convection is actually exchanged. Microphysical variables such as hydrometeor size, fall velocity and shape (in the case of ice particles) can influence evaporation and sublimation and hence the water vapor transport and the heating profile. Those uncertainties can place severe limitations to our capabilities of modeling tropical convection. Even in a framework in which the heating and moistening is controlled by an imposed forcing on the large−scale, such as cloud−resolving simulations, the microphysics is also important when coupled to the radiation, as shown, for instance, by Grabowski et al. (1999) and Wu et al. (1999). Surprisingly, however, there are only few and insufficient microphysical observations in the tropics. Among those observations are some microphysical studies performed during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE, e.g., Takahashi et al. 1995), measurements in tropical cumulonimbi during the Stratosphere−Troposphere Exchange Project (STEP, Knollenberg et al. 1993) and microphysical data collected during the Central Equatorial Pacific Experiment (CEPEX, Chen et al. 1997). Those observations generally revealed important peculiarities in the microphysical evolution of tropical convective clouds, such as extremely high concentrations of ice crystals. In Brazil, microphysical data are even scarcer. The Ceará Experiment in 1994 (Costa et al. 2000) provided information on the microphysics of clouds over Northeast Brazil, but focused on warm−phase microphysical processes only. No significant microphysical studies were performed over the Amazon region until recently, especially concerning mixed−phase (liquid water and ice) convective clouds. Convection over the Amazon Basin has unique characteristics in terms of its organization and heating patterns. For instance, Greco et al. (1994) show that Amazon coastal squall lines exhibit heating profiles that depart from both oceanic convection and convection from other continental regions. Amazon convection has very distinctive features related to the presence of the forest and some of them have direct impact over the characteristics of convection, such as the strong heat fluxes (e.g., Abreu Sá et al. 1988, Martin 1988, Viswanacham et al. 1990) and the significant production of aerosols by both natural and burning emissions (e.g., Kaufman et al. 1998, Ramer et al. 1998, Artaxo et al. 1998, Echalar et al. 1998). This justifies a thorough analysis not only of the dynamics and thermodynamics of Amazon convection but also of its microphysics. To what extent the microphysics of Amazon convection is influenced by its dynamics and can in turn influence the larger scales is still unknown. In this context, the Tropical Rainfall Measuring Mission Large Scale Biosphere−Atmosphere Experiment in Amazonia (TRMM− LBA) provided the first opportunity to extensively investigate the microphysical structure of Amazon convection. Using the TRMM−LBA data, important uncertainties regarding the microphysical aspects of Amazon convection can be addressed, for instance, the characteristic number concentration and size, size distribution and more common shapes of the ice crystals. In this paper, microphysical observations of cumulus convection microphysics over Amazonia collected during the TRMM−LBA are analyzed with emphasis on the ice phase. Its outline is as follows. Section 2 describes the instrumentation used in the TRMM−LBA microphysical field campaign. Sections 3 and 4 show results from one case |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://ams.confex.com/ams/pdfpapers/42138.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
