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Fred M. Vukovich

Abstract

Ground temperatures and reflectivity patterns have been examined for the area in and surrounding St. Louis, Missouri, using HCMM satellite data. Analyses demonstrate marked seasonal and day/night differences. In the warm season and during the day, the ground temperature distribution is influenced by small-scale land use features. The temperature contrast between the urban and rural region averages about 4.3°C. In the cold season and during the daytime, the pattern is similar to that found in the warm season, but the temperature contrasts are not as large (the temperature contrast between the urban and rum region is 2.4°C). At night, the ground temperature pattern does not show a strong dependence on small-scale land-use features. The temperature contrast between the urban and rural regions is about 2.5°C, which is similar to that found in the cold season during the day.

The reflectivity is low in the central portion of St. Louis and in other smaller urban areas surrounding St. Louis. Difference in reflectivity between the center of St. Louis and the surrounding suburban and rural regions ranges from 2 to 4 percentage points, similar to albedo differences observed by White et al. (1978) and Dabberdt and Davis (1974).

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Fred M. Vukovich

Abstract

A simple linear model is developed to study the transient response of the atmosphere, a system of internal gravity waves, due to mid-tropospheric heating. The effects of varying stability, mean wind, the horizontal and the vertical distribution of the heating, and the rate at which heat is added are presented. It was found that under certain conditions specifically related to the vertical thickness of the heated layer and the stability of the air, the vertical velocities in the upper and lower atmosphere attain magnitudes in excess of 3 m sec−1. The magnitude of the vertical velocities will increase further if the rate at which heat is added is increased. Decreasing the horizontal dimensions of the region where heat is added does not change the magnitude of the vertical velocities appreciably except for the gravity wave with the largest vertical wavelength; however, the horizontal scale of the gravity wave system is smaller, and wave speeds are less since they are proportional to horizontal wavelength.

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Fred M. Vukovich

Abstract

The life cycle of a cold perturbation on the boundary of the Loop Current in the Gulf of Mexico was studied over the period of 18 March to 22 May 1984, approximately a 60-day period. The study focused on the behavior of the surface and subsurface area of the cold perturbation as it moved along the boundary of the Loop Current. The area of the perturbation was defined by an alongflow-scale length, which is the scale length parallel to the unperturbed flow of the Loop Current, and the crossflow-scale length, which is the scale length perpendicular to the unperturbed flow of the Loop Current. The area of the perturbation remained relatively unchanged as the perturbation moved along the Loop Current boundary and reached the region off the Dry Tortugas; however, when the perturbation reached the Dry Tortugas, the orientation of the perturbation changed, suggesting a method whereby elongated cold perturbations form off the Dry Tortugas. Shortly thereafter, the area of the perturbation began to decrease, signaling the decay of the perturbation.

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FRED M. VUKOVICH

Abstract

A simple linear model was used to determine the influence of a pressure-dependent friction term on the steady-state solution for long waves produced by heating. Resonance effects, which are found in a frictionless atmosphere, were also evident in the case when friction was concentrated in the boundary layer. As friction increased at low pressure, resonance effects were no longer apparent.

Net potential and kinetic energy changes did not occur when friction was zero. When friction was allowed, the conversion term for potential energy was balanced by the generation term and the northward heat transport term. The net frictional loss of kinetic energy was balanced by the conversion of potential energy into kinetic energy.

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Fred M. Vukovich

Abstract

A study of a cold eddy on the eastern side of the Gull Stream was performed combining data from the NOAA 2 and NOAA 3 satellites and from the Cape Fear Technical Institute's R/V Advance II. The satellite data were used initially to identify and locate the eddy in real-time. The location data obtained from the satellite imagery was used to plan an oceanic field program using the Advance II to collect temperature and salinity data in the perturbation.

The analysis of satellite data indicated that the cold eddy was elliptic in shape with the major axis varying from 180 to 120 km and a minor axis varying from 120 to 100 km. The analysis also suggested that the circulation of the eddy was entraining warm Gulf Stream water, strengthening the warm ring around the eddy. The subsurface analysis indicated that the cold eddy was characterized by a very pronounced dome of relatively cold, less saline water below 200 m. Above 200 m, the temperature and salinity were uniform, both vertically and horizontally.

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FRED M. VUKOVICH

Abstract

A theoretical technique was employed to compute the magnitude of the effect of cloud interference on the Nimbus High Resolution Infrared Radiometer (HRIR) data. A comparative study using HRIR and ground truth data suggests that the derived results could be used successfully as an analysis tool to discriminate cloud-contaminated temperatures from clear-sky temperatures provided an estimate of the cloud cover and type is available.

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Fred M. Vukovich

Abstract

Simple linear models were used to study the effect of wind shear on the nocturnal urban heat island circulation. It was shown that the intensity of the urban heat circulation decreases by increasing the magnitude of the bulk shear through the boundary layer, if the heating rate is constant. However, if the difference between the mean temperature in the urban and environmental boundary layer and the stabilities are identical in two separate cases, the case with the stronger shear will have a stronger urban heat island circulation.

When the magnitude of the vertical velocity was computed, it was found that the results were contingent on the boundary conditions used to solve the second-order equations for the motion. In the case where the perturbation vertical and horizontal velocities were set to zero at the surface, both the vertical scale and the intensity of the circulation approached infinity as the characteristic Richardson number approached zero. When the rigid lid concept was employed to limit the vertical scale of the circulation, a critical Richardson number existed in stable air for which the circulation had a finite maximum intensity. The value of the critical Richardson number was a function of the vertical scale of the rigid lid, and for a given vertical scale, there was more than one value for the critical Richardson number. The most intense circulation was found when the critical Richardson number was small.

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FRED M. VUKOVICH

Abstract

A simple two-dimensional linear model was used to explore the nature of the heat island circulation of an urban area. Two stability categories, stable and near-neutral, were assumed to define the boundary layer conditions. The heat island circulation was studied under the condition of no-mean wind and also for cases when a mean wind existed. The forcing function (differential heating) was given as a smoothly varying function in the horizontal that would create a smoothly varying temperature field with no discontinuities in the temperature distribution. A rather weak two-cell circulation system was developed in which depth and intensity were dependent on the boundary layer stability. Allowing a mean wind to exist produced a displacement of the two-cell circulation downstream to a location that is a function of the heating rate and the advection of heat and momentum by the mean wind.

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Fred M. Vukovich

Abstract

A climatology of various ocean features in the Gulf of Mexico (GOM) was developed using the combination of satellite remote sensing and in situ data that spanned periods as long as 32 years. Twelve separate statistics were created, some of which described characteristics of the Loop Current, while others are involved with warm core rings that separate from the Loop Current and cold core rings. These statistics examined the frequency with which the Loop Current was found in the GOM, the orientation of the Loop Current, the frequency of intrusion of Loop Current water onto the west Florida shelf and into the GOM common water region, ring separation period from the Loop Current, ring dissipation, ring speed, ring path, frequency of ring water in the western GOM, and the frequency of warm and cold core rings (WCRs and CCRs, respectively) in the GOM. The results indicate that CCRs were principally responsible for mass and heat redistribution in the eastern GOM (EGOM) and WCRs are responsible for mass and heat redistribution in the western GOM (WGOM). The average period for WCR separation from the Loop Current was 11 months and the range from 5 to 19 months. WCRs moved through the WGOM most often using the central path (i.e., their trajectory was found between 24° and 26°N latitude) and they decreased to about 55% of their initial size when they reach the western wall of the GOM. CCRs were most often found in the EGOM, and their frequency of occurrence in the EGOM surpassed that of WCRs anywhere in the GOM.

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FRED M. VUKOVICH

Abstract

The variation of the differential heating required to depict the diurnal behavior of the urban heat island is established from temperature data obtained in the literature and from other sources. A simple, linear, three-layer model was developed to study the response of the urban atmosphere to the differential heating in the no-mean-wind case. The only driving force in the model was differential heating. The solutions suggest that the urban atmosphere experiences a short period of upward vertical motion in the early evening (the urban heat island circulation) in response to the positive differential heating at this time and a short period of downward vertical motion in the late morning in response to the negative differential heating at that time. The latter response would prevent diffusion of pollutants in the vertical and would bring an elevated pollution layer over the city to the surface. Therefore, the dynamic response could be responsible for the production of a “critical episode” in the city.

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