This study refers to developed ecological model abroad, and established the seagrass model with MATLAB compiler. I also took the seagrass meadows in south Taiwan-Nanwan for my studying case, and simulated the dynamic effect of seagrass and epiphyte biomass, as well as nutrient, and attempted to go on probing into the cause with northeast monsoon and typhoon. The simulating site of this study was Nanwan, which is located at Hengchun Peninsula, the southern tip of Taiwan. The dominant species in this area is Thalassia hemprichii. South Taiwan is situated at a tropical climate, and the variation of air temperature is small. Additionally, Kurshio embranchment cause the variation of water temperature smaller, about 24 (¢J) to 30 (¢J).The northeastern monsoonal winds, formed downhill winds, are extremely forceful from October to April, so the wind speed is greater during this period than the rest of the year. In South Taiwan, dry-wet season is clearly. The dry season is from November to April, and the wet season is from May to October. The main rainfall comes from southwest monsoon, especially summer typhoon (June to September). The wind speed is raised abruptly by typhoon and makes water agitate, which not only cause the mortality raising but also the sediment turbulence. By Lin¡¦s research (2005), the growing area of seagrass meadow in Nanwan is a half-closed tidal pool where human makes huge effect and there is a lot of drainage of house and inn sewage. Furthermore, these seagrasses in Nanwan would be exposed to air during the period of poor tide and the emerged period is the longest of these three areas -Nanwan, Dakwan and Wanliton. The seasonal dynamic of seagrass, which is located in the high site of intertidal zone, is obvious, and the biomass is larger in summer than in winter; but that is not obvious in the low site and tidal pool. By the seasonal condition and some specially climate condition mentioned above, the analysis of simulate cases would be go on. Comparing of the modeling result and real measurement, the seasonal changing situation mostly match up. No matter high site (emerged and dried) or low site, there is the maximum of seagrass biomass (including above ground, below ground, or shoot density) in summer, and the minimum in winter. Typhoon causes the biomass losing abruptly in summer. R/S ratio (below-ground biomass division above-ground biomass) is bigger in winter than in summer. On one hand the inside nitrogen redistribution is larger in summer, because the larger growth rate occurs in summer, and the more nutrient is supplied from roots, on the other the redistribution is smaller in winter cause the less nutrient is supplied from roots. Epiphyte biomass has the maximum in summer, when the nutrient concentration of water is larger. In the section of the difference between low and high site seagrass, it is apparent that the high site seagrass would be exposed to air and dried by northeast monsoon. Although typhoon comes up, its influence is not so strong as northeast monsoon at high site. The maximum biomass still occurs in summer, and it is presumed that the living environment of high site seagrass is with more pressure by nature. The above-ground biomass of high site seagrass is smaller than low site, but the below-ground biomass is much lager at high site. Besides, shoot density is larger at high site. The biomass of epiphyte is larger at low site just opposite to shoot density. It is supposed that high site seagrass is emerged to air and limited by environment factors so above-ground biomass would be reduced and store up the sustenance to below-ground biomass. It is conjectured that the main factor with shoot density is affected by light density and below-ground biomass. In shallow water, the seagrass at high site could accept more light energy, moreover the below-ground biomass is sufficient and the recruitment rate is large, thus there are more shoots at high site. Epiphytes are also limited by water depth and wind, and the biomass of epiphyte at high site is smaller than at low site.

Abstract The South China is the largest marginal sea in the western Pacific. It¡¦s unique geographic settings and high sedimentation rates preserve the paleo- climatic signals with larger amplitude than those from the open ocean. In this study, grain size and elemental compositions of the fine fractions (<63 mm) from the sediments collected by the ODP Leg 184 Sites 1143 and 1146 were analyzed to reconstruct the depositional settings for the last 8 My. Particle size and elements analyses, in conjunction with the carbonate contents and sedimentation rates from core sediments, reflect the possible increase in precipitation, which was caused by the strengthened summer monsoon between 5 and 3 Ma. In addition to the grain sizes change from silt-domain to clay-domain, Ti/Al ratio of sediments increase while the Si/Al, Zr/Al, and K/Al ratios decrease, which could be related to the enhanced sediments input through rivers. These environmental changes could be attributed to the uplift of Tibet plateau and the formation of Western Pacific Warm Pool. On the contrary, the impact of climate changes is not evident in the loess plateau in the northwestern China. It is likely that the climate in the South China Sea became warm and humid from 5 to 3 Ma were regional changes. Key words: Grain size, element analyses, South China Sea, summer monsoon

Orography plays a major role in the general circulation and climate of the tropics. Although many works have been done on the impact of global orography on summer monsoon, the previous studies have examined the impact on seasonal mean scale or only during the first half of the season. Role of orography on intra-seasonal variability has not been addressed previously. Also, the proximate and remote impacts of orography have not been studied. In this thesis an atmospheric General Circulation Model (GCM) has been used to investigate the impact of global and regional orography on monsoon climate. Two different cumulus schemes have been used to study the sensitivity of the results to the cumulus parameterization scheme. The model was forced with seasonally varying sea surface temperature (SST) for the year 1998. An ensemble simulation of 5 members were performed for each experiment. The simulations showed that the removal of Himalayas or orography over the entire earth caused a delay of about one month in the onset of the monsoon. The delay in monsoon onset was on account of a more stable atmosphere due to intrusion of mid-latitude cold air into the Indian region in the absence of Himalayas. After the onset, the precipitation rate was comparable in control and no-mountain simulations. The seasonal mean (June-September) precipitation over this region decreased by 25% in the no-mountain case as compared to control. A comparison of the impact of east and west Himalaya orography showed that orography west of 80E has more impact on the phase and intensity of summer monsoon precipitation over the Indian region than orography east of 80E. The onset of summer monsoon over the Indian region was delayed by about one month with the removal of Himalaya orography west of 80E, but was delayed by just about one week with the removal of Himalaya orography east of 80E. This is because, the cold air intrusion was more when Himalaya orography west of 80E was removed. Seasonal mean precipitation decreased by 22% and 12% with the removal of orography west and east of 80E respectively. Himalaya orography east of 80E showed more influence on precipitation over the north-east Indian region and East Asia. The removal of orography from the African continent increased the summer monsoon precipitation over the Indian region. This was on account of an increase in the zonal mass flux from the African continent in the absence of East African mountains. This mass flux brings more moisture into the south Asian region and increases precipitation over the Indian region and Bay of Bengal. A higher precipitation over the Bay of Bengal leads to higher wind over the Somalia coast and this acts as a positive feedback to enhance the summer monsoon precipitation by about 28% over the Indian region. The presence of orography only over the African continent resulted in the largest delay in the monsoon onset (by 50 days) and the lowest amount of seasonal precipitation (decrease by 36%) over the Indian region among all the simulations. This is due to further reduction in zonal mass (and hence, moisture) flux toward the Indian subcontinent with the inclusion of African orography when compared with no-global orography simulation. The seasonal mean precipitation decreased by 19% over the Indian region with the removal of American orography. The onset of monsoon was delayed by about 3 weeks in this experiment as compared to control. This delay was due to a relative downward motion in the upper troposphere on account of the shift of the Rossby wave with the removal of American mountains. In this thesis, a new theory has been proposed for monsoon onset based on thermodynamic conditioning (necessary condition) and mechanical trigger (sufficient condition) of the atmosphere. This theory was able to explain the large variation in monsoon onset dates (maximum spread 57 days) in different simulations. The low level circulation was affected more by Himalaya orography west of 80E, which had a profound influence on precipitation over the Indian region. However, upper level circulation was affected more by Himalaya orography east of 80 E. The northward shift of the upper tropospheric westerly jet during the Northern Hemispheric summer was sudden in presence of the Tibetan Plateau and gradual in its absence. This shift was not related to the onset of monsoon over the Indian region. Northward propagation of convection was found to be present even in the absence of global orography. But northward extent of this propagation was delayed without orography on account of the absence of a favorite meridional gradient of moist static energy in the lower troposphere in the early summer season due to intrusion of mid-latitude cold air. Space-time spectral analysis showed that the intensity of eastward moving convectively coupled atmospheric waves, known as Madden-Julian oscillation (MJO), decreased in absence of global orography. Moreover, the presence of orography favor the higher zonal wave number for MJO propagation.

Thunderstorms that occur in areas of complex terrain are a major severe weather hazard in the intermountain western U.S. Short-term quantitative estimation (QPE) of precipitation in complex terrain is a pressing need to better forecast flash flooding. Currently available techniques for QPE, that utilize a combination of rain gauge and weather radar information, may underestimate precipitation in areas where gauges do not exist or there is radar beam blockage. These are typically very mountainous and remote areas, that are quite vulnerable to flash flooding because of the steep topography. Lightning has been one of the novel ways suggested by the scientific community as an alternative to estimate precipitation over regions that experience convective precipitation, especially those continental areas with complex topography where the precipitation sensor measurements are scarce. This dissertation investigates the relationship between cloud-to-ground lightning and precipitation associated with convection with the purpose of estimating precipitation- mainly over areas of complex terrain which have precipitation sensor coverage problems (e.g. Southern Arizona).The results of this research are presented in two papers. The first, entitled Toward Development of Improved QPE in Complex Terrain Using Cloud-to-Ground Lighting Data: A case Study for the 2005 Monsoon in Southern Arizona, was published in the Journal of Hydrometeorology in December 2012. This initial study explores the relationship between cloud-to-ground lightning occurrences and multi-sensor gridded precipitation over southern Arizona. QPE is performed using a least squares approach for several time resolutions (seasonal -June, July and August-, 24 hourly and hourly) and for a 8 km grid size. The paper also presents problems that arise when the time resolution is increased, such as the spatial misplacing of discrete lightning events with gridded precipitation and the need to define a "diurnal day" that is synchronized with the diurnal cycle of convection. The second manuscript (unpublished), entitled An Improved QPE Over Complex Terrain by Using Cloud-to-Ground Lightning Occurrences, provides a new method to retrieve lightning-derived precipitation at 5 minutes and 5 Km time and space resolutions. A stationary model that employs spatio-temporal neighboring (Space and Time Invariant model -STI) improves upon the least squares method in the first paper. By applying a Kalman filter to the STI model, lightning-precipitation is retrieved by a dynamic model that changes in time. The results for seasonal and 5 minutes time resolution show that the dynamic model improves the retrievals derived by the STI model.

Streams and groundwaters interact in distinctly different ways during flood versus base flow periods. Recent research in the Upper San Pedro River using isotopic and chemical data shows that (1) near-stream, or 'riparian,' groundwater recharged during high streamflow periods is a major contributor to streamflow for the rest of the year, and (2) the amount of riparian groundwater derived from this flood recharge can vary widely (10-90%) along the river. Riparian groundwater in gaining reaches is almost entirely basin groundwater, whereas losing reaches are dominated by prior streamflow.This description of streamflow gives rise to the questions of (1) how much flood recharge occurs at the river-scale, and (2) subsequently, what is the relative importance of flood recharge and basin groundwater in maintaining the hydrologic state of the riparian system. To address these questions, a coupled hydrologic-solute model was constructed for 45 km of the Upper San Pedro riparian system.

Precipitation (P) and precipitable water (W) are important components of the hydrological cycles in the earth system, and their seasonal cycles are closely related to monsoon circulations over monsoon regions. Through theoretical analyses and extensive analysis of data from in-situ measurements, satellite remote sensing, and regional reanalysis, significant progress has been made (via four peer-reviewed publications) in four areas related to P, W, and monsoon onset and retreat. First, based on the normalized W index, a novel unified method is proposed to determine global monsoon onset and retreat dates. The results are consistent with those obtained from different local criteria. Second, theoretical and data analyses demonstrate that, because of the large annual range of temperature, W can increase from winter to summer anywhere except in the tropics, including both monsoon and nonmonsoon regions. Third, while the seasonal variation of P is, in general, caused by complex processes (e.g., atmospheric circulations), thermodynamic derivations and data analysis demonstrate that the variation of P from winter to summer can be easily understood from the comparative strength between the change of water vapor and the change of temperature. In monsoon regions, the change of water vapor from winter to summer is much greater than the change of temperature, so P has an in-phase relation with W. While in some of the nonmonsoon regions, where winter is the rainy season, the change of temperature is much greater than the change of water vapor, leading to an out-of-phase relation between P and W, and, relative to summer, the coldness of the winter air is much more significant than its dryness. Finally, the satisfactory performance of the globally unified monsoon index can be understood by comparing the seasonal cycles of P and W. The significant positive correlations between P and W at seasonal and synoptic scales imply that W has the ability to indicate both the means and the interannual variations of the monsoon onset and retreat. Since large increase of W from winter to summer can occur in both monsoon and nonmonsoon regions, the global monsoon regions cannot be obtained from the seasonal change of W.

Thesis (M. S.)--Earth and Atmospheric Sciences, Georgia Institute of Technology, 2010. / Committee Chair: Peter J. Webster; Committee Member: Judith A. Curry; Committee Member: Robert X. Black. Part of the SMARTech Electronic Thesis and Dissertation Collection.

A commonly noted problem in the simulation of warm season convection in the North American monsoon region has been the inability of atmospheric models at the meso- scales (10 s to 100 s of kilometers) to simulate organized convection, principally mesoscale convective systems. With the use of convective parameterization, high precipitation biases in model simulations are typically observed over the peaks of mountain ranges. To address this issue, the Kain-Fritsch (KF) cumulus parameterization scheme has been modified with new diagnostic equations to compute the updraft velocity, the convective available potential energy closure assumption, and the convective trigger function. The scheme has been adapted for use in the Weather Research and Forecasting (WRF). A numerical weather prediction-type simulation is conducted for the North American Monsoon Experiment Intensive Observing Period 2 and a regional climate simulation is performed, by dynamically downscaling. In both of these applications, there are notable improvements in the WRF model-simulated precipitation due to the better representation of organized, propagating convection. The use of the modified KF scheme for atmospheric model simulations may provide a more computationally economical alternative to improve the representation of organized convection, as compared to convective-permitting simulations at the kilometer scale or a super-parameterization approach.

The effects of enhanced greenhouse gas concentrations on Earth’s climate are well understood. However, the impacts of anthropogenic aerosol particles, in particular due to the many aerosol-cloud indirect feedback mechanisms are not fully or even explicitly quantified as yet. This PhD seeks to contribute to improve our knowledge and understanding of aerosol – precipitation interactions over the Nepal Himalayas region and their consequences for precipitation patterns there. The research was carried out using the cloud-resolving Weather Research and Forecasting (WRF) model through a series of sensitivity studies and supported by literature reviews of satellite and field observations, although the latter are sparse. To complement the modelling studies, from March to December 2011, aerosols and surface meteorology were also continuously measured at Nagarkot (Lat: 27.7°N, Lon: 85.5° E, Alt: 1900m), Nepal, located in the eastern flank of a bowl shaped Kathmandu valley. The location was chosen to provide a representative vertical profile of aerosol and the impact on topographical flows. Our results showed a unique pattern of diurnal pollution circulation within the valley with a morning and evening peak. The evening peak, which is higher than the morning peak is attributed to the light wind blowing through the valley carrying locally generated fresh evening pollution, further enhanced by re-circulations of aged pollutants through suppression of the mixing layers as suggested by a previous study at a different location. The morning peak is caused by calm wind conditions followed by the transitional growth of the nocturnal boundary layer. It is found that the thermally driven mountain – valley wind circulations are responsible for ventilation of pollutants. The WRF simulations showed that a sophisticated double moment bulk microphysics parameterization scheme performed best, which did not show any statistically significant difference compared to the observed data at 80% confidence interval using a Chi-squared goodness of best fit test. A sensitivity analysis of aerosol and temperature perturbations on the monsoon precipitation was conducted. We found that the model represented the first indirect effect reasonably well however, rainfall was not particularly sensitive to the aerosol perturbations used, due to the poorly documented role of the ice phase processes which assume a greater importance in this region due to the influence of topography and diurnal heating cycle. Further model studies focusing on chemical properties of aerosol and sensitivity of Ice Nuclei (IN) to precipitation in this region are recommended. In contrast, the effects of temperature perturbation were found to be significant, more so than the currently modelled aerosol indirect effects, suggesting that reduced frequency but intense rain events are likely over the Himalayas as the climate warms.

Geprägt wird das Klima auf dem Indischen Subkontinent ganz erheblich durch den Einfluss des Monsuns, der ein Teilelement des gesamten asiatischen Monsunsystems ist. Der Monsun hat als wesentlicher Klimafaktor einen wichtigen Einfluss auf die geomorphologische Entwicklung der Flüsse und Flusstäler des Indischen Subkontinents in Verbindung mit den Überschwemmungen, die durch die Niederschläge des Monsuns verursacht werden.