Convective clouds in the tropics can be grouped into three categories: shallow clouds with cloud-top heights near 2 km above the surface, mid-level congestus clouds with tops near the 0°C level, and deep convective clouds capped by the tropopause. This trimodal distribution is visible in cloud data from the Geoscience Laser Altimeter System (GLAS), carried aboard the Ice, Cloud, and land Elevation Satellite (ICESat), as well as in precipitation data from the Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR). Fractional areal coverage (FAC) data is calculated at each of the three levels to describe how often optically thick clouds or precipitation are seen at each level. By dividing the FAC of TRMM PR-observed precipitation by the FAC of thick GLAS/ICESat-observed clouds, the fraction of clouds that are precipitating is derived. The tropical mean precipitating cloud fraction is low: 3.7% for shallow clouds, 6.5% for mid-level clouds, and 24.1% for deep clouds. On a regional basis, the FAC maps created in this study show interesting trends. The presence of nonphysical answers in the PCF graphs, however, suggest that greater study with more precise instruments is needed to properly understand the true precipitating cloud fraction of the tropical atmosphere.

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Predicting the amount of solar radiation that reaches the earth’s surface is critical to understanding the performance of solar power systems, and cloud cover has a particularly strong impact on both the amount and direction of this radiation. Due to its variable nature, solar power is typically thought of as able to provide electricity only as a supplement to traditional power sources. However, by incorporating energy storage into solar facility design, it is possible to mitigate the variations in power production due to changes in sunlight. A key question then is how much energy storage would be required to account for daily solar irradiance variations and allow a solar power facility to produce electricity at least 80% of the year, comparable to traditional coal and natural gas plants. I have developed a simple algorithm for computing the intensity and angular distribution of light transmitted through, and reflected from, clouds. This result allows for accurate determination of variations in irradiance values across the globe. I have also created a model for the energy produced from a 100MW(e) solar power facility coupled to a large-scale thermal energy storage system. I used daily solar irradiance values to determine the array size needed at every location on the planet, and compared the power output at every location when both 1200MWh(e) and 1800MWh(e) of storage were incorporated into the plant design. I then computed the fraction of the year that power was produced at the rated capacity and the amount of time before the facility energy requirements are recouped. My analysis shows that more than 69% of the global land mass has sufficient solar resources provide continuous electricity output more than 80% of the time, and 27% of the land mass can do this more than 90% of time. In these locations the energy payback time ranges from 1.75 to 10 years. / text

Supersoft and quasisoft X-ray sources are collectively known as Very Soft X-ray Sources (VSSs) characterized by their considerably lower effective temperatures than normal X-ray emitting objects and the lack of significant emission above 1 keV, with measured temperatures ranging from about tens to less than about 300 eV, respectively. They are defined observationally and believed to be associated with a wide variety of astrophysical systems such as white dwarfs, neutron stars, and black holes. VSSs have been identified in our own Galaxy, the Magellanic Clouds, and other external galaxies. Due to the vicinity of the Magellanic Clouds and the low associated absorption of soft X-ray photons, they are unique in the studies of VSSs. However, no attempt has been made to search for VSSs and investigate the source population in the Magellanic Clouds using all the available archival data. A systematic survey of VSSs in the Magellanic Clouds was therefore performed using data from both XMM-Newton and Chandra. VSSs were identified by selection algorithim based on X-ray hardness ratio after the background galaxies and foreground stars were filtered. A total of 47 new supersoft and 75 new quasisoft candidates were identified. Six of them were strong enough for spectral analysis with derived temperatures of 15 – 250 eV and luminosities of of 3.5 ×?10?^34– 5.4 ×?10?^36 erg s^(-1). The softest and brightest candidate represents a promising supersoft candidate with a possible UV counterpart identified with XMM-Newton Optical Monitor having an estimated UV luminosity of ~2.7 ×?10?^35 erg s^(-1). The large dataset also allows the long-term studies of some of the previously identified supersoft X-ray sources. Through the comprehensive survey with multi-epoch data, an X-ray/UV stellar flare was discovered and its analysis is also reported. / published_or_final_version / Physics / Master / Master of Philosophy

This thesis is an observational investigation into the origin of large-scale coherent magnetic fields in the Milky Way and the Magellanic Clouds. I use Faraday rotation measure of both polarized extragalactic sources and that derived from diffuse polarized synchrotron emission as probes of interstellar magnetism. Rotation measure uniquely provides the magnetic field direction in the diffuse interstellar medium, which cannot be achieved using other observing techniques. Using extragalactic source rotation measures behind the Small Magellanic Cloud (SMC), I find a large-scale coherent magnetic field in this irregular galaxy, where the classic dynamo effect is expected to be weak. I suggest that the cosmic-ray driven dynamo, which relies heavily on cosmic ray pressure to generate poloidal fields could be in operation. By analyzing rotation measures derived from diffuse polarized emission from the Large Magellanic Cloud (LMC) simultaneously with rotation measures of 100 extragalactic sources behind it, I conclude that the LMC has a quadrupolar-type magnetic field structure, in accord with predictions from dynamo theories. However, the field amplification time scale of a classic dynamo is too long compared to frequent tidal-triggered star forming episodes experienced by the LMC which can prevent any large-scale coherent field from building up. I propose that the cosmic-ray driven dynamo, which has a much shorter amplification time scale than the classic dynamo, could be the origin of the observed coherent fields in the LMC. The dynamo theory predicts a symmetric vertical magnetic field across the galactic disk for Milky Way-type galaxies. However, based on rotation measures of 1,000 extragalactic sources toward the Galactic poles, I find a lack of vertical field symmetry across the Galactic mid-plane. I suggest that the observed RMs could be the superposition of a symmetric disk field and an anti-symmetric field produced by a separate dynamo effect in the Galactic halo. Furthermore, I demonstrate that existing Galactic halo magnetic field models cannot successfully reproduce extragalactic rotation measures at mid-Galactic latitudes in the second Galactic quadrant. I propose that halo fields consist of magnetic spirals could potentially account for the observed RM pattern. / Astronomy

Rapid population growth in Arizona is leading to increasing demand and decreasing availability of water, requiring a detailed quantification of hydrological processes. The integration of detailed spatial water fluxes information from remote sensing platforms, and hydrological models is one of the steps towards this goal. One example step is the use of MODIS Snow Cover Area (SCA) information to update the snow component of a land surface model (LSM). Because cloud cover obscures the images, this project explores a rule-based method to remove the clouds. The rules include: combination of SCA maps from two satellites; time interpolation method; spatial interpolation method; and the probability of snow occurrence in a pixel based on topographic variables. The application in sequence of these rules over the Upper Salt River Basin for WY 2005 resulted in a reduction of cloud obscuration by 93.7878% and the resulting images' accuracy is similar to the accuracy of the original SCA maps. The results of this research will be used on a LSM to improve the management of reservoirs on the Salt River. This research seeks to improve SCA data for further use in a LSM to increase the knowledge base used to manage water resources. It will be relevant for regions were snow is the primary source of water supply.

Cirrus clouds are known to play a key role in the earth's radiation budget, yet are one of the most uncertain components of the earth-atmosphere system. With the development of instruments such as the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) and the Moderate-resolution Infrared Spectroradiometer (MODIS), scientists now have an unprecedented ability to study cirrus clouds. To aid in the understanding of such clouds, a significant study of cirrus radiative properties has been undertaken. This research is composed of three parts: 1) the retrieval of tropical cirrus optical thickness using MODIS level-1b calibrated radiance data, 2) a survey of tropical cirrus cloud cover, including seasonal variations, using MODIS level-3 global daily gridded data, and 3) the simultaneous retrieval of cirrus optical thickness and ice crystal effective diameter using AVIRIS reflectance measurements.

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No description available.

Orographic cloud is investigated in a global context using both observations and a global climate model. Climatological cloud amounts from the International Satellite Cloud Climatology Project (ISCCP) are used in conjunction with wind reanalyses to study orographic cirrus amounts over the globe. Significant increases in cirrus are seen over many land areas, with respect to any surrounding oceans. To aid in interpretation of this result special attention is given to the New Zealand region as a case study for orographic cloud formation. Cirrus is found be more prevalent over New Zealand when compared to the adjacent ocean to the west. ISCCP cloud amounts are also compared with a ten year simulation of the UK Meteorological Office's Unified Model. The model is found to be considerably lacking in both cirrus and total high cloud over major mountain ranges. The model is also found to lack trailing cirrus clouds in the lee of orography despite the inclusion of a prognostic ice variable capable of being advected by the model winds. To improve the simulations of orographic cirrus and high cloud in the Unified Model a linear hydrostatic gravity wave scheme that predicts both the amplitude and phase of subgrid orographic gravity waves is introduced. The temperature perturbation caused by these waves in the troposphere is used to modify the amount of both liquid and ice cloud. One important feature of the parameterisation is that the launch amplitude of the gravity waves is predicted by a directional variance function which accounts for anisotropy in the subgrid orography. The parameterisation is explored in the context of an off-line testbed before implementation in the Unified Model. In a ten year simulation the parameterisation is found to increase the high cloud amounts over a number of the world's major mountain ranges. However, this extra cloud is optically thick and unable to remove the deficiency in optically thin cirrus amounts. Suggestions, as part of future work, for improvements to the model and orographic cloud parameterisation are also made.