Donner, Leo J., Charles J Seman, Richard S Hemler, and John P Sheldon, 1997: Radiative transfer in a three-dimensional cloud-system-resolving model In IRS '96: Current Problems in Atmospheric Radiation, Proceedings of the International Radiation Symposium, Fairbanks, Alaska, 19-24 August 1996. Hampton, Deepak Publishing, 109-112. Abstract
A three-dimensional, non-hydrostatic cloud-system-resolving model is used to study radiative transfer in convective systems. The model domain covers approximately 50,000 km2. Prognostic equations determine the evolution of liquid and ice mixing ratios. The three-dimensional distribution of liquid and ice is used in shortwave and long-wave radiative-transfer calculations.
A tropical convective system with a mesoscale anvil circulation is analyzed. The distribution of radiative forcing is examined, and its role in the evolution of the convective system is considered.
Donner, Leo J., Charles J Seman, and John P Sheldon, 1997: Cloud-radiative interactions in high-resolution cloud-resolving models In 9th Conference on Atmospheric Radiation, Boston, MA, American Meteorological Society, 47-48. PDF
Orlando, J J., and John P Sheldon, 1995: Stages in the energetics of baroclinic systems. Tellus A, 47A(5), 605-628. Abstract
The results from several idealized and case studies are drawn together to form a comprehensive picture of "downstream baroclinic evolution" using local energetics. This new viewpoint offers a complementary alternative to the more conventional descriptions of cyclone development. These additional insights are made possible largely because the local energetics approach permits one to define an energy flux vector which accurately describes the direction of energy and quantifies the role of neighboring systems in local development. In this view, the development of a system's energetics is divided into three stages. In Stage 1, a pre-existing disturbance well upstream of an incipient trough loses energy via ageostrophic geopotential fluxes directed downstream through the intervening ridge, generating a new energy center there. In Stage 2, this new energy center grows vigorously, at first due to the convergence of these fluxes, and later by baroclinic conversion as well. As the center matures, it begins to export energy via geopotential fluxes to the eastern side of the trough, initiating yet another energy center. In Stage 3, this new energy center continues to grow while that on the western side of the trough decays due to a dwindling supply of energy via fluxes from the older upstream system and also as a consequence of its own export of energy downstream. As the eastern energy center matures, it exports energy further downstream, and the sequence begins anew. The USA "Blizzard of '93" is used as a new case study to test the limits to which this conceptual sequence might apply, as well as to augment the current limited set of case studies. It is shown that, despite the extraordinary magnitude of the event, the evolution of the trough associated with the Blizzard fits the conceptual picture of downstream baroclinic evolution quite well, with the geopotential fluxes playing a critical role in three respects. First, fluxes from an old, decaying energy center there and modifying the jet, resulting in a large extension of the overall kinetic flow were strongly convergent over the west coast of North America, creating a kinetic energy center well into Mexico. Second, energy fluxes from this extension of the northwesterly flow were strongly convergent east of the trough, producing explosive growth of kinetic energy over the northwestern Gulf of Mexico, with baroclinic conversion following shortly thereafter. Lastly, the kinetic energy generated by the vigorous baroclinic conversion in the cold advection on the west side of the trough was very effectively transferred to the energy center on the east side of the trough via geopotential fluxes.
Numerical simulations have been made of the initiation of a strong ridge-trough system over western North America and the eastern Pacific (the terminus of the Pacific storm track), with the objective of determining the extent to which downstream development contributed to its growth, and the possible influence of topography on the energetics of the storm. While a control simulation demonstrated considerable skill in reproducing the storm, a "simplified" simulation in which topography, surface heat fluxes, and latent heating were removed not only reproduced the primary features of the ridge-trough system- permitting a clearer interpretation of the factors contributing to its growth- but actually generated a stronger system, suggesting that these effects as a whole inhibited storm development. Application of an energy budget that distinguishes between energy generation via the convergence of geopotential fluxes revealed that early growth of the system was dominated by flux convergence. These findings are in agreement with the results of previous studies that have shown that eddies near the downstream end of a storm track grow, at least initially, primarily through the convergence of downstream energy fluxes. Baroclinic conversion, mostly in the form of cold advection, became the primary energy source only after the development was well under way. This sequence of initial energy growth via flux convergence followed by additional contributions by by lower-level baroclinic conversion comprise a a process designated "downstream baroclinic development" (DBD). A similar analysis of the control simulation showed that the energy budget was essentially the same, with the exception of baroclinic conversion, which was more significant early in the eddy's development due to orographic lifting of warm westerly flow. The decay of the storm in both simulations was mainly the result of flux divergence after the storm reached maturity, although this process was somewhat delayed in the control case because of larger fluxes resulting from the dispersion of additional kinetic energy generated by latent heat release upstream from the system. It is believed that the techniques employed here could represent a valuable new tool in the study of the development of such baroclinic systems and the diagnosis of model deficiencies.
The GATE analysis was repeated utilizing the full GATE data set in the delayed mode and a revised four-dimensional analysis procedure. The reulting maps were compared with maps of other authors. Based on the new analysis, macroscale circulation features for the tropical African continent and Atlantic Ocean region were calculated, and other characteristic phenomena of this area were investigated. The easterly waves, in particular, were studied with respect to their formation, propagation, associated condensation, and possible conversion to hurricanes. It was possible to trace nine distinct easterly waves throughout their entire life history, and the analyzed tracks of these easterly waves agreed quite well with the subjective analyses of Sadler and Oda (1978). The time sequences of precipitation over the GATE A/B-array obtained by the present analysis and by satellite estimates were compared with some success.
