Relationships between kinematics, microphysics, and lightning in high plains storms observed during the severe thunderstorm electrification and precipitation study

Summer 2006.Includes bibliographical references (pages 168-169).The Severe Thunderstorm Electrification and Precipitation Study (STEPS) was established to improve our understanding of electrification mechanisms and lightning in High Plains storms. In particular, STEPS focused on investigating anomalous positive cloud-to-ground (CG) lightning, which had been documented to occur more often in this region than in the rest of the U.S. Radar and lightning observations of four storms observed during the STEPS field campaign are analyzed and discussed. The four cases include a predominantly positive CG-producing (PPCG) supercell on 29 June, a supercell on 3 June that produced no CG lightning of either polarity, a negative CG-producing multicellular storm on 19 June, and a PPCG multicellular storm on 22 June. Data from multiple Doppler radars have been synthesized to calculate the three-dimensional wind field, polarimetric radar variables have been combined with thermodynamic soundings to estimate hydrometeor types throughout the echo volumes, and Lightning Mapping Array (LMA) data have been sorted into flashes and studied to determine the flash rates and charge structure for several hours of each storm's lifetime. The purpose of this study is to determine what features are unique for storms that produce predominantly positive CG lightning, and attempt to reveal the processes that lead to this behavior. The 29 June supercell produced large amounts of hail and frequent positive CG lightning, as well as exhibited a large volume of strong (> 10 m S-1) updraft and a deep region of cyclonic vertical vorticity. The charge structure of the 29 June supercell was inverted, with a main region of positive charge centered near 8 km MSL with a negative charge layer above and below. The inferred charge structure in the 3 June case consisted of an inverted dipole, with positive charge beneath upper-level negative charge. A lower negative charge layer was not detected in 3 June and may have been the reason for the lack of CG lightning. This case produced some hail, but not as much hail volume as 29 June, and the updraft volume and cyclonic vertical vorticity were dramatically lower as well. The 19 June multicellular storm exhibited a normal charge structure, with main negative charge centered at 7 km MSL, and positive charge layers above and below, and therefore produced mostly negative CG lightning. The storm produced negligible hail, and had very weak and shallow updrafts, yielding near zero values of strong updraft volume. The 22 June multicellular storm exhibited both inverted and normal charge structures in different regions of the storm complex. The volume of strong updraft was very high, similar to that of 29 June, and the storm produced ample amounts of hail. Both positive and negative CG lightning was observed in this storm complex, but the majority of the CG lightning was of positive polarity. The results indicate that PPCG storms tend to have larger updrafts (both wider and larger in volume), which is consistent with previous studies. Large updrafts and enhanced vertical vorticity also play an important role in the production of large hail. Furthermore, low-level negative charge (below a larger region of positive charge) was observed in the cases that produced positive CG lightning, which may be the impetus needed for the flash to come to ground. This lower negative charge, in essence, represents the lowest charge layer of an inverted tripolar charge structure. The charge structures observed during the production of negative CG lightning were a normal tripole (with negative charge situated between upper and lower positive charge layers) on 19June and an inverted dipole (with negative charge above positive) in the anvil on 22 June. Cloud-to-ground flash rates (of either polarity) decreased when either the lower charge layer of the corresponding tripolar structure was absent, or when the low-level charge layer exhibited an enhanced number of LMA sources, in which case intra-cloud (IC) discharges seemed to be preferred between the two lowest charge layers of the tripole

Kinematic and microphysical evolution of the 29 June supercell observed during STEPS

Spring 2003.Also issued as Sarah A. Tessendorf's thesis (M.S.) -- Colorado State University, 2003.Includes bibliographical references.The focus of this thesis is to examine the kinematic and microphysical properties of a severe storm using polarimetric and Doppler radar data. The data were collected during the Severe Thunderstorm Electrification and Precipitation Study (STEPS) that took place between 17 May 2000 and 20 July 2000 in eastern Colorado and western Kansas. One goal of STEPS is to find a relationship between the microphysics and kinematics of severe storms on the High Plains and their unusual positive cloud-to­ ground lightning production. The severe storm observed on 29 June 2000 produced large hail, frequent positive cloud-to-ground lightning, an F1 tornado, and displayed characteristic storm splitting evolution during the sampling period. Unprecedented measurements from three Doppler radars were used to describe the kinematics and rnicrophysics of this storm. Radial components of the wind fields relative to the three Doppler radars were combined to produce the three-dimensional winds in the storm. Bulk precipitation types (e.g., rain, hail) were objectively determined using the multi­ parameter variables available on two of the radars. The Doppler-derived kinematic fields were compared with the microphysical classifications over a nearly three-hour period to examine trends during the lifecycle of the supercell. Results showed that the supercell intensified rapidly while storm splitting occurred. Prior to splitting, there was little cloud-to-ground lightning and little evidence of hail aloft. After storm splitting. hail volume and cloud-to-ground lightning activity quickly intensified. The updraft of this storm pulsated, with maximum speeds to nearly 50 m s·1. The peaks in hail production aloft, largely around -10° C, were well correlated with the updraft fluctuations as well as with peaks in the frequency of positive cloud-to­ ground lightning flashes. These results are consistent with experimental work that shows positive charging in ice-ice collisions around -10° C. The dynamics of the storm-splitting process, in terms of radar-derived updraft and vorticity fields, were shown to be consistent with current conceptual models. The results of this thesis advance our knowledge of supercell evolution and will be used to help determine the electrification mechanisms of severe storms that produce predominantly positive cloud-to-ground lightning.Sponsored by the National Science Foundation under grant ATM-9912051

Strahlungsbilanz arktischer Bewölkung aus Modell und Beobachtung

The effects of clouds and sea-ice on the surface radiative balance in the Arctic are studied. Clouds during arctic summer are characterized by a low optical thickness and high cloud amounts. To determine the effect of these clouds in combination with sea-ice, measurements onboard the research vessel FS Polarstern were obtained in August and September 2009 during the expedition ARK24-3 in the Greenland Sea. Data evaluation was accompanied by model calculations with the radiative transfer model GRIMALDI. In particular, the effect of multiple reflexions between sea-ice surface and clouds on the shortwave radiative balance was determined. The GRIMALDI model from R. Scheirer is based on the Monte-Carlo method and was adjusted within this work to radiative transfer calculations in the broadband solar spectrum. The average downward shortwave and longwave irradiance of 80W/m2 and 296W/m2 measured during ARK24-3, as well as the average sea-ice albedo of 0.45 at this time of the year are within the scope of expectations from previous studies (Intrieri et al., 2002b; Shupe and Intrieri, 2004; Wang and Key, 2005; Persson et al., 2002). This applies also for the shortwave and longwave cloud radiative forcing (-70W/m2 and 46W/m2) which depends not only on sun zenith angle but also from surface albedo and temperature. For zenith angles less than 82°, surface cloud radiative forcing had a cooling effect during ARK24-3 and for zenith angles greater than 82° a warming effect. Sea-ice increases the downward shortwave irradiance at the surface by multiple reflexions between sea-ice and clouds. In case of a broken cloud cover the effect is amplified in places where the irradiance is already increased due to cloud distribution. In the local mean, the effect depends on the cloud cover and the optical thickness of clouds. The absolute magnitude of the effect increases with cloud fraction. With an increasing optical thickness, the relative magnitude of the effect increases, while the absolute irradiance decreases. This results in an optical thickness tau with a maximal increase of the absolute sea-ice effect. This optical thickness is near tau = 5 which equals the average optical thickness of clouds during ARK24-3. With a zenith angle of theta = 60°, sea-ice albedo of 0.5 and 100% cloud cover the total increase is 45W/m2, representing a relative increase of the downward irradiance of 15%. With the effect of increased downward shortwave irradiance over sea-ice compared to water, a difference in the cloud radiative forcing is to be expected. This difference was not observed during ARK24-3. Because of the small dataset it remains uncertain if this is due to additional low-level clouds over sea-ice or to increased cloudiness in relation with frontal systems

An exploration of the role of uniforms in contributing to the embedding and transmitting of organizational culture

Many companies today are using some form of uniforms for employees. This research is an exploration of the role of uniforms in contributing to the embedding and transmitting of organizational culture. Culture is the experiences and common learning of the organization that results in shared values and beliefs. According to Schein (1985: 14) culture has three levels, namely: artifacts, values, and basic underlying assumptions. The first level of the culture consists of the physical constructs of the organization, and therefore includes the uniforms, which is the focus of this study. Schein (1985: 223) further proposes that culture can be embedded and transmitted through various mechanisms. The research was conducted in the constructivist paradigm, at a tertiary institution of higher learning in Eastern Cape, South Africa. To ensure triangulation, three sources of data were used, namely: documentation; observation; and both individual and focus group interviews. The researcher argues that uniforms played a role in the embedding of the sample organization’s three levels of culture, which were expressed in terms of Hofstede’s (1991: 07) culture dimensions. Firstly, the use of the different uniforms by different groups, as well as the ranking indicated by the uniforms, played a role in embedding the high power distance culture. Secondly, the symbolism of security portrayed by the uniform played a role in embedding the high uncertainty avoidance culture. Thirdly, it was found that the uniform created unity amongst groups, resulting in greater expression of collectivism. Fourthly, the use of sensible and practical uniforms plays a role in embedding the feminine culture where competitiveness is avoided and relationships are nurtured. Lastly, the uniform plays a possible role in transforming the culture from short-term to a long-term orientation that focuses on the future

An analysis of the development model for ex-farmworkers and adjacent communities in the Indalo association of private game reserves in the Eastern Cape

Over the past fifteen years there has been an extensive conversion of land use from traditional farming practices to conservation and private game reserves. It has been suggested by Langholz and Kerley (2006:2) that privately owned preserved areas can engage in ecotourism initiatives by protecting biodiversity, succeeding financially and contributing to social upliftment. However, ecotourism has to operate within the context of historical land dispossession of the majority black population and current land reform initiatives to address this problem. In view of the economic, social and environmental importance of ecotourism based private game reserves (PGRs) in South Africa, particularly the Eastern Cape, the main goal of this research is to examine the Indalo association of private game reserves in the Eastern Cape Province’s development model for ex-farmworkers and adjacent communities. This was done through a literature survey and analysis of existing studies and by interviewing the managers of the Indalo PGRs and a few farmworkers to get their opinions of the tension between what they are doing and the imperatives of land reform. This involved an exploration of their community development work, particularly around issues of job creation, participation in decision-making, capacity building and sustainability. The thesis comes to the following conclusions. The first is that the establishment of PGRs have a significant positive impact on the local areas in which they are established. As a land-use, ecotourism based game reserves are an economically and ecologically desirable alternative to other land uses. Therefore the ecotourism based private game reserve industry with its extensive community development focus for farmworkers and local communities is a viable and sustainable alternative to conventional land reform. The second is that the Indalo PGRs development work has built capacity in the communities it has served. However, community participation, particularly in decision-making is limited and needs more attention if productive and sustainable development is to be achieved. Lastly, communities rely heavily on external support for their development and upliftment. However, the majority of the PGRs have/or are putting measures in place to ensure the continuation of community development projects to ensure the long-term sustainability of projects

Modeling of blood flow in the microcirculation

Call number: LD2668 .T4 1985 T47Master of Scienc

Estimating the willingness-to-pay for restoring indigenous vegetation at selected sites in South Africa

The Working for Water (WfW) Programme is a public works programme designed to clear South Africa of invasive alien vegetation and to restore lowwater consuming indigenous vegetation in the areas that have been cleared. Funds to clear alien invasives were initially secured on the basis that such a programme would increase water runoff, facilitate biodiversity and ecosystem functioning, and provide social benefits through job creation. The economic merits of the Programme, in terms of increased water yields, has been established in the Western Cape and KwaZulu-Natal, but questioned in the Eastern and Southern Cape. However, there are economic aspects of the studies carried out in the Eastern and Southern Cape that merit more attention than was given them; one of these being the issue of non-water benefits. Preliminary figures emanating from contingent valuation pilot studies conducted at six WfW projects sites indicated that one of these non-water benefits, namely the biodiversity and ecosystem resilience benefit, could be substantial. As such, the primary objective of the present study was to apply the contingent valuation method (CVM) to value people’s preference for indigenous vegetation. This value was intended to serve as a proxy for increased biodiversity and ecosystem resilience at three WfW sites. Despite the controversy surrounding the CVM, it has been found that it is a credible valuation tool. The CVM’s merits lie in its versatility and in the fact that it is the only method available which is capable of obtaining estimates of both nonuse and use values, thus making it applicable for valuing biodiversity. The primary aim of a CVM study is to determine an estimate of the total willingness-to-pay (WTP). In this study, the total WTP figure was calculated by multiplying the median WTP for the local WfW Programme by the total number of user households. The respective total WTP amounts are shown in Table 1. It was anticipated that respondents would be willing to pay more for the national WfW Programme, than for the less inclusive good (i.e. the local WfW Programme). The results correspond with this expectation at the Port Elizabeth and Underberg sites. However, due to strategic factors Worcester respondents were willing to pay more for the local WfW Programme than for the national Programme

Water wave packets

This paper presents a method for simulating water surface waves as a displacement field on a 2D domain. Our method relies on Lagrangian particles that carry packets of water wave energy; each packet carries information about an entire group of wave trains, as opposed to only a single wave crest. Our approach is unconditionally stable and can simulate high resolution geometric details. This approach also presents a straightforward interface for artistic control, because it is essentially a particle system with intuitive parameters like wavelength and amplitude. Our implementation parallelizes well and runs in real time for moderately challenging scenarios