Cloud Resolving Models use microphysics parameterisation schemes for the simulation of clouds. The thesis reports on the introduction of two single-moment Bulk Microphysics Parameterisation (BMP) schemes in the Nonhydrostatic - coordinate Model (NSM). The rst BMP is known as the PURDUE-LIN scheme, and can be used with ve (excluding graupel) or six (including graupel) classes of the water substance. The second scheme was developed using the PURDUELIN scheme as a starting point, and is known as SBU-YLIN. Graupel and snow share a category and processes in the latter scheme. Simulations of two hours in length are made, with convection initiated through inserting a warm thermal into a cooler environment, using a six-class and ve-class PURDUE-LIN and the SBU-YLIN BMPs. The simulations are performed at various horizontal resolutions of 500 m, 1 km and 2 km. The six-class PURDUE-LIN scheme simulates more rainfall than the ve-class PURDUE-LIN and the SBU-YLIN schemes. The SBU-YLIN scheme generally rains the least, looses the least water vapour to hydrometeors and warms up the least. The PURDUE-LIN schemes simulate two convective cells in a no shear environment. The maximum updrafts associated with the rst cell (triggered by the warm perturbation) are similar in all the simulations. The second cell is triggered by a cold pool. While the cold pool is stronger in the six-class PURDUE-LIN scheme simulations, the updrafts in the second cell are stronger in the ve-class PURDUE-LIN simulation. The SBU-YLIN scheme generally simulates just one cell because of a weak cold pool. Simulations were also made for three di erent periods dominated by suppressed convection with deep convection at the beginning and end of the three periods, forced with large scale tendencies observed during the Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA COARE). The NSM is able to capture di erences in the suppressed and deep convection periods. Qualitatively, the simulations provide new insight into the interplay between cloud microphysics and cloud dynamics, and points out the potential for better describing the uncertainty range associated with projections of future climate change, through the improvement and stochastic application of cloud microphysics schemes. / Thesis (PhD)--University of Pretoria, 2013. / gm2013 / Geography, Geoinformatics and Meteorology / unrestricted

京都大学 / 新制・課程博士 / 博士(理学) / 甲第23712号 / 理博第4802号 / 新制||理||1687(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 竹見 哲也, 准教授 重 尚一, 教授 榎本 剛 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The giant planets exhibit banded zonal jet streams that have maintained theirstructures over decades. There are long-standing questions: how deep the windstructures extend? What mechanisms generate and maintain the observed winds?Why are the wind structures so stable? To answer these questions, we performedthree-dimensional numerical simulations of the atmospheric flow using the primitiveequations.First, we use a simple Newtonian cooling scheme as a crude approach to gener-ate atmospheric latitudinal temperature differences that could be caused by latentheating or radiation. Our Jupiter-like simulations show that shallow thermal forcingconfined to pressures near the cloud tops can produce deep zonal winds from thetropopause all the way down to the bottom of the simulated atmosphere (a fewhundred bars). These deep winds can attain speeds comparable to the zonal jetspeeds within the shallow, forced layer; they are pumped by Coriolis accelerationacting on a deep meridional circulation driven by the shallow-layer eddies.Next, we explicitly include the transport of water vapor and allow condensationand latent heating to occur whenever the water vapor is supersaturated. Our simu-lations show that large-scale moist convection associated with condensation of watervapor can produce multiple zonal jets similar to those on the gas giants (Jupiterand Saturn) and ice giants (Uranus and Neptune). For plausible water abundances(3-5 times solar on Jupiter/Saturn and 30 times solar on Uranus/Neptune), oursimulations produce about 20 zonal jets for Jupiter and Saturn and 3 zonal jetson Uranus and Neptune. Moreover, these Jupiter/Saturn cases produce equatorialsuperrotation whereas the Uranus/Neptune cases produce equatorial subrotation,consistent with the observed equatorial jet direction on these planets. Sensitiv-ity tests show that the water abundance is the controlling factor; modest waterabundances favor equatorial superrotation, whereas large water abundances favorequatorial subrotation. This provides a possible mechanism for the existence ofequatorial superrotation on Jupiter and Saturn and the lack of superrotation onUranus and Neptune.

MENVSC / Department of Geography and Geo-Information Sciences / Out of all rain-producing weather systems, cut-off lows (COLs) are linked with the occurrence of high impact rainfall and in some cases short-lived floods which can last for 24 hours over South Africa. This study examined the characteristics associated with the present occurrence of the severe COL systems over South Africa from 2011 to 2017. The accuracy of the 4.4 km Unified Model (UM) which is currently in use for simulating areas of deep moist convection in South Africa was evaluated. The UM simulated geopotential height at 500 hPa as well as the associated 24 hours precipitation which were compared against the daily fields of geopotential height and 6-hourly precipitation from the European Centre for Medium-Range Weather Forecasts (ECMWF). COL events were categorized and analyzed according to the associated surface circulation patterns at 850 hPa. The seasonal distribution and duration of the systems over northern (10°E-33°E //22°-32°S) and southern (10°E-33°E //32°-35°S) regions of the study area were also analyzed. Results show COL systems shifting with season towards the north eastern parts of the country, with an increased number of events during the austral winter season during the study period. Systems which lasted for long time were observed during the austral winter and spring seasons. The UM tends to simulate areas of heavy precipitation accurately with poor simulation during the initial stages of the systems. The UM provided a more realistic-looking closed geopotential height and rainfall fields for systems which are coupled with a cold front at the surface. Application of the knowledge about the evolution in the characteristics of COL events from this study can improve the operational forecasting of these weather systems over the country. / NRF