Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Meteorology. / Microfiche copy available in Archives and Science. / Bibliography: leaf 76. / by Gerald Francis Riley, Jr. / M.S.

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Tropical cyclone (TC) size is integral in determining the spatial extent of TC impacts and is influenced by environmental wind shear and the overall moisture environment. Since initial TC size is related to future TC size, research focused on understanding the influences of TC size away from land can lead to a more complete understanding of the extent of coastal impacts associated with landfalling TCs. This study considers TCs located in an area of low to moderate wind shear located at least 100 km from major land masses. An empirical orthogonal function (EOF) analysis is used to distinguish different environments based on the large-scale spatial pattern of total column water vapor (TCWV) surrounding the TC. Using these EOF patterns, four separate categories (groups) are created. Principal component (PC) scores indicate the time steps most contributing to the EOF pattern for each group and ultimately determine the time steps included in each group. TC sizes among the groups are compared using size metrics based on the wind field and shape metrics based on the precipitation field. These metrics are considered at the central timestep identified in the EOF analysis as well as a 48-hour window centered on the central timestep. There are no significant differences in the wind field size, but TCs with moisture to the southeast are the largest in terms of overall precipitation area. This suggests that moisture affects the size of the precipitation field but not the wind field. However, more research is needed to confirm this relationship. Storms with moisture to the southeast are also more intense and younger than TCs in other groups and show signs of inner core organization and subsequent intensification while TCs in the other groups do not. TCs in an extremely dry environment or with dry air to the southeast of the TC center are generally smaller, less closed, less solid, and older than TCs with moisture to the southeast and TCs with dry air to the northwest of the TC center. An additional analysis comparing the same size and shape metrics between TCs experiencing easterly and westerly shear is also completed. The wind shear results suggest that, while easterly shear is more commonly associated with younger and intensifying TCs regardless of moisture group, an environment with westerly shear is more favorable for intensification of TCs with moisture to the southeast due to the alignment of moisture and upward motion. Future work will investigate the physical processes contributing to these precipitation shape and size differences between groups and wind shear directions. / Master of Science / The size of tropical cyclones (TCs) is heavily influenced by moisture and wind shear. Wind shear is defined as the changing of wind direction with vertical height in the atmosphere. Research focused on investigating how moisture and wind patterns affect the size and structure of TCs can lead to a better understanding of the physical extent of impacts associated with landfalling TCs and advise more effective emergency preparedness plans. This research considers TC time steps located over the ocean and in a calm wind environment. From here, time steps are divided into four groups representing common moisture patterns in the Atlantic basin. TC size is evaluated using size and shape metrics designed to capture the spatial extent and layout of wind and rain associated with the storm. This research also compares the evolution of these size and shape metrics to better understand how the environment around the TC changes over time. Results show that the extent of wind associated with the storm is similar across all groups but TCs with moisture to the southeast are the largest in terms of overall rain area. This suggests that moisture affects the extent of precipitation but not the extent of wind or that wind data are inaccurate. Additionally, TCs with moisture to the southeast are younger and stronger than storms in the other groups. TCs in extremely dry environments and TCs with dry air to the southeast are generally smaller, weaker, and older than TCs in the other groups. In looking at the evolution of these size and shape metrics, TCs with moisture to the southeast group become stronger with time while TCs in the other groups do not. An additional analysis comparing TCs experiencing different wind patterns is completed. Results of this show that, while easterly wind shear, characterized by surface winds out of the west and upper level winds out of the east, is more commonly associated with strengthening TCs when moisture is not considered, TCs with moisture to the southeast in an environment with westerly wind shear are more likely to strengthen over time due to the alignment of moisture with favorable environmental conditions within the storm by the overall wind pattern. Westerly shear is characterized by winds at the surface out of the east and upper level winds out of the west. Future work should focus on the environmental processes contributing to the size and shape differences observed between moisture groups and wind patterns.

<p> This thesis is concerned with the cooperative growth problem of the discontinuous precipitation reaction. Previous theories are examined, and the kinetic details of a model, which assumes the existence of a metastable monotectoid reaction and the adherence & local equilibrium, are derived. As with other attempt to describe the parameters of duplex growth situations we cannot find a unique relation between the rate of growth and the lamellar spacing. The various optimal or variational procedures used to remove this degree of freedom are considered. The Cu-In system is subject to quantitative experimental study, and the extent of interference of the concurrent general precipitation reaction is determined. Finally the kinetic data and auxiliary information are used to test the various theories. </p> / Thesis / Doctor of Philosophy (PhD)

This thesis investigates the potential for fouling in plain and augmented tubes in cooling tower applications. Three primary factors that affect fouling potential are examined: inside tube geometry, water velocity, and water quality. This paper presents a literature survey for in general precipitation fouling, particulate fouling, cooling water fouling, and fouling in enhanced tubes. This thesis also attempts to determine water qualities that are typical of those found in actual cooling towers. The water quality was determined by taking water samples from cooling towers throughout the country and chemically analyzing the samples. From this analysis, three water qualities were determined: an average fouling potential, a low fouling potential, and a severe fouling potential. These water qualities will be used in experimental determinations of fouling resistances in augmented tubes.

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As population and urbanization increase across the United States, the effects of natural hazards may well increase, as extreme events would increasingly affect concentrated populations and the infrastructure upon which they rely. Extreme precipitation is one natural hazard that could stress concentrated populations, and climate change research is engaging heavy precipitation frequency and its impacts. This research focuses on the less-studied phenomenon of an extreme precipitation reversal - defined as an unusually wet (dry) period that is preceded by an unusually dry (wet) period. The magnitude is expressed as the difference in the percentiles of the consecutive periods analyzed. This concept has been documented only once before in a study that analyzed extreme precipitation reversals for a region within the southwestern United States. That study found that large differences in precipitation from consecutive winters, a hydrologically critical season for the region, occurred more frequently than what would be expected from random chance, and that extreme precipitation reversals have increased significantly since 1960. This research expands upon the previous work by extending the analysis to the entire continental United States and by including multiple temporal resolutions. Climate division data were used to determine seasonal and annual precipitation for each of nine climate regions of the continental United States from 1895-2014. Precipitation values were then ranked and given percentiles for seasonal and annual data. The season-to-season analysis was performed in two ways. The first examined consecutive seasons (e.g., winter–spring, spring–summer) while the second analyzed the seasonal data from consecutive years (e.g., spring 2014–spring 2015). The annual data represented precipitation for the period October 1–September 30, or the 'water year' used by water resource managers. Following the approach of the previous study, a secondary objective of the research was to examine large-scale climate teleconnections for historical relationships with the occurrence of precipitation reversals. The El Nino-Southern Oscillation was chosen for analysis due to its well-known relationships with precipitation patterns across the United States. Results indicate regional expressions of a propensity for extreme precipitation reversals and relationships with teleconnections that may afford stakeholders guidance for proactive management. Precipitation reversal (PR) and extreme precipitation reversal (EPR) values were significantly larger for the second half of the study period for the western United States for the winter-to-winter, spring-to-spring, and year-to-year analyses. The fall-to-fall analysis also revealed changes in PR/EPR values for several regions, including the northwest, the Northern Rockies and Plains, and the Ohio Valley. Relationships between the winter-to-winter PR time series and an index representing the El Nino-Southern Oscillation (ENSO) phenomenon were examined. The winter-to-winter PR time series of the Northern Rockies and Plains region and the South exhibited significant relationships with the time series of Niño 3.4 values. El Niño (La Niña) coincided with more wet-to-dry (dry-to-wet) PR/EPR values for the Northern Rockies and Plains, while El Niño (La Niña) coincided with more dry-to-wet (wet-to-dry) PR/EPR values for the South. / Master of Science

Precipitation is one of the atmospheric variables that characterize the climate of a region. The South Island of New Zealand (SI of NZ) has an unusually large number of distinct regional climates and its climatic diversity includes the coldest, wettest, driest and windiest places in New Zealand. This thesis focuses on identifying precipitation trends and rainfall fluctuations for the SI of NZ. First, homogeneity of 184 precipitation series is assessed with the combination of three homogeneity tests (Standard Normal Homogeneity Test, Easterling & Peterson test, Vincent�s Multiple Linear Regression). More than 60% of tested time series are found to contain at least one inhomogeneity. About 50% of the inhomogeneities can be traced to information in the station history files with nearly 25% of all inhomogeneities caused by the relocation of the precipitation gauge. Five coherent precipitation regions are defined by the Principal Component Analysis. The objective of identifying the periods of water deficit and surplus in spatial and temporal domains is achieved by using Standardized Precipitation Index (SPI). The SPI series (for 3, 6, 12, 24 and 48 months time scales) are calculated for each region and used for analysis of dry and wet periods. Clear differences in the frequency, length and intensity of droughts and wet periods were found between individual regions. There is a positive (i.e. increase in wet periods) trend in SPI time series for the North, Westland and Southland regions during the 1921-2003 period at all times scales, and a negative trend for Canterbury during the same period. The results show longer wet periods than dry periods at all time scales. Extreme heavy precipitation, which causes floods, is the most common type of natural disaster accounting for about 40% of all natural disasters worldwide. A set of ten extreme indices is calculated for 51 stations throughout the South Island for the period 1951-2003. The west-east division is found to be the dominant feature of extreme precipitation trends for all extreme indices with more frequent and more intense extreme precipitation in the west/southwest and with a declining trend in the east. The significant decrease in extreme precipitation frequency was detected in Canterbury with 3 days less of precipitation above the long-term 95th percentile by 2003 as compared to 1951. The variability of precipitation, expressed by the SPI, is correlated with local New Zealand atmospheric circulation indices and large-scale teleconnections. The precipitation variability in the South Island is governed largely by the local circulation characteristics, mainly the strength and position of the westerly flow. The increase in precipitation in the West and SouthEast is associated with enhanced westerlies. The correlations between New Zealand�s circulation indices and regional SPI are seasonally robust. The SouthEast region exhibits a strong relationship with the Southern Oscillation Index on seasonal and annual time scales,and with Interdecadal Pacific Oscillation at the decadal scale. The predictability of seasonal precipitation one season ahead is very limited.