Browsing by Author "Vonder Haar, Thomas H., author"
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Item Open Access A bi-spectral method for cloud parameter determination(Colorado State University. Libraries, 1976) Reynolds, David W., author; Vonder Haar, Thomas H., author; Department of Atmospheric Science, Colorado State University, publisherItem Open Access A study of cloud classification with neural networks using spectral and textural features(Colorado State University. Libraries, 1999) Bian, Bin, author; Shaikh, Mukhtiar A., author; Azimi-Sadjadi, Mahmood R., author; Vonder Haar, Thomas H., author; Reinke, Donald L., author; IEEE, publisherThe problem of cloud data classification from satellite imagery using neural networks is considered in this paper. Several image transformations such as singular value decomposition(SVD) and wavelet packet (WP) were used to extract the salient spectral and textural features attributed to satellite cloud data in both visible and infrared (IR) channels. In addition, the well-known gray-level cooccurrence matrix (GLCM) method and spectral features were examined for the sake of comparison. Two different neural-network paradigms namely probability neural network (PNN) and unsupervised Kohonen self-organized feature map (SOM) were examined and their performance were also benchmarked on the geostationary operational environmental satellite (GOES) 8 data. Additionally, a postprocessing scheme was developed which utilizes the contextual information in the satellite images to improve the final classification accuracy. Overall, the performance of the PNN when used in conjunction with these feature extraction and postprocessing schemes showed the potential of this neural-network-based cloud classification system.Item Open Access A study of tropical cyclone structural evolution(Colorado State University. Libraries, 2006) Maclay, Katherine S., author; Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisherThe destructive potential of a tropical cyclone is highly dependent on both the intensity and size of the storm. There has been extensive research done on intensity and intensity change, but far less work has focused on tropical cyclone structure and structural changes. The recent highly active Atlantic tropical seasons reemphasize the need for a better understanding of tropical cyclone structural evolution. This is particularly true of the 2005 season which produced a number of storms, such as Katrina, Rita, and Wilma, that not only became extremely intense, but also grew substantially in size during intensification. In contrast to these giants are the storms such as Hurricanes Charley (2004) and Emily (2005), which reached equal intensity, but remained fairly small in size. The goal of this study is to gain a better understanding of what causes these different structural evolutions in tropical cyclones. The inner core (0-200 km) wind-fields of Atlantic and Eastern Pacific tropical cyclones from 1995-2005 from aircraft reconnaissance flight-level data is used to calculate the low-level inner core kinetic energy. An inner core kinetic energy-intensity relationship is defined which describes the general trend of tropical cyclone inner core kinetic energy (KE) with respect to intensity. However, this mean KE/intensity relationship does not define the evolution of an individual storm. The KE deviations from the mean relationship for each storm are used to determine the cases where a storm is experiencing significant structural changes. The evolution of the KE deviations from the mean with respect to intensity indicates that hurricanes generally either grow and weaken or maintain their intensity, or strengthen but do not grow at the same time. The data is sorted by the state of intensification (intensifying, weakening, or maintaining intensity) and structure change (growing or non-growing), defining six sub-groups. The dynamic, thermodynamic, and internal conditions for the storm sub-groups are analyzed with the aid of statistical testing in order to determine what conditions are significantly different for growing versus non-growing storms in each intensification regime. These results reveal that there are two primary types of growth processes. The first is through eyewall replacement cycles, an internally dominated process, and the second via external forcing from the synoptic environment. As a supplement to this study, a new tropical cyclone classification system based on inner core KE is presented as a complement to the Saffir-Simpson hurricane scale.Item Open Access An analysis of two years of Nimbus 6 Earth radiation budget observations: July 1975 to June 1977(Colorado State University. Libraries, 1980) Campbell, G. G., author; Vonder Haar, Thomas H., author; Department of Atmospheric Science, Colorado State University, publisherItem Open Access An investigation of the radiative boundary conditions during the development of the southwest monsoon Saudi Arabian heat low(Colorado State University. Libraries, 1981-07) Smith, Eric A., author; Sakkal, M. Marwan, author; Ackerman, Steven A., author; Cox, Stephen K., author; Vonder Haar, Thomas H., authorProgress report no. 1 on the cooperative research project between the Department of Atmospheric Science at Colorado State University and the Faculty of Meteorology and Environmental Science at King Abdul-Aziz University in accordance with the CID-ARME TED Project of the University of Arizona. Period covered February 15 to August 15, 1981.Item Open Access An investigation of the radiative boundary conditions during the development of the southwest monsoon Saudi Arabian heat low(Colorado State University. Libraries, 1982-01) Smith, Eric A., author; Ackerman, Steven A., author; Cox, Stephen, K., author; Vonder Haar, Thomas H., author; Sakkal, M. Marwan, author; Department of Atmospheric Science, Colorado State University, publisherProgress report no. 2 on the cooperative research project between the Department of Atmospheric Science at Colorado State University and the Faculty of Meteorology and Environmental Science at King Abdul-Aziz University in accordance with the CID-ARME TED Project of the University of Arizona. Period covered August 16-November 30, 1981.Item Open Access Annual report for 1987 from the Cooperative Institute for Research in the Atmosphere, Colorado State University, to Marine Meteorology Section, Ocean Sciences Division of the Office of Naval Research on studies of space/time variability of marine atmospheric boundary layer characteristics(Colorado State University. Libraries, 1988-03) Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisherItem Open Access Atlas of radiation budget measurements from satellites (1962-1970)(Colorado State University. Libraries, 1974) Vonder Haar, Thomas H., author; Ellis, James S., author; Department of Atmospheric Science, Colorado State University, publisherItem Open Access Climatology of radiation budget measurements from satellites(Colorado State University. Libraries, 1980) Campbell, G. G., author; Vonder Haar, Thomas H., author; Department of Atmospheric Science, Colorado State University, publisherItem Open Access Cloud and convection frequencies relative to small-scale geographic features(Colorado State University. Libraries, 1990-01) Gibson, Harold M., author; Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisherVisible and infrared data of GOES West were collected for nine hours each day during the summer of 1986. Cloud frequency charts were computed for the area from Mississippi east to Georgia and the Gulf of Mexico north to Tennessee for each of the nine hours as well as convection frequency charts to four convection intensities as defined by the temperature of the cloud top. Strong diurnal tendencies were noted. As was expected, these charts show that over the land areas cloudiness is at a maximum during the early afternoon hours with convection at a maximum in the late afternoon and evening. Cloudiness and convection are at a maximum during the nocturnal hours over the Gulf of Mexico. Cloud frequency shows a strong relationship to small terrain features. Small fresh water bodies have cloud minima in the afternoon hours relative to the surrounding terrain while higher terrain, especially if there is a sharp slope, have cloud maxima. The adjacent lower terrain exhibits afternoon cloud minima due to divergence caused by the valley to mountain breeze. The sea breeze-induced convergence causes relative cloud maxima over near-shore land areas with the stronger maxima over peninsulas. It is shown that the sea breeze results in convergent low level flow regardless of the weather over a peninsula or over land adjacent to a bay or inlet. Cloud frequencies tend to be larger both in magnitude and areal extent over peninsulas. Small scale geographical features show no relationship to convection, but larger peninsulas and extensive higher terrain show late afternoon convection maxima.Item Open Access Compositing digital satellite data to detect regions of orographically induced convection on the northern High Plains(Colorado State University. Libraries, 1982) Klitch, Marjorie A., author; Vonder Haar, Thomas H., author; Department of Atmospheric Science, Colorado State University, publisherItem Open Access Description of the cloud layer experiment (CLEX), field phase, surface data archive(Colorado State University. Libraries, 1996-12) Cox, Stephen K., author; Gillies, John M. Davis Sean, author; Huffman, Arlie, author; Kleist, John, author; Wood, David, author; Wood, Norm, author; Vonder Haar, Thomas H., authorItem Open Access Direct readout meteorological satellite data processing with a low-cost, computer-linked system(Colorado State University. Libraries, 1974) Vonder Haar, Thomas H., author; Lilie, L., author; Reynolds, David W., author; Department of Atmospheric Science, Colorado State University, publisherItem Open Access Diurnal cycle of tropical deep convection examined using high space and time resolution satellite data(Colorado State University. Libraries, 1997-09) Hall, Timothy J., author; Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisherInfrared (IR) and visible (VIS) satellite data from GMS-4 with 5-km spatial and 1-hr temporal resolution was used to examine the diurnal cycle of deep convection over a sector of the tropical west Pacific warm pool (WP) bounded by 140°-180°E, 0°-20°N. Data were analyzed for 45 days of summer from 22 June 1994 - 5 August 1994 (JJA) and for 65 days of winter between 28 November 1994 – 31 January 1995 (NDJ). The synoptic backdrop for JJA was characterized by the monsoon trough, oriented northwest to southeast through the WP. Convection was largely focused along the trough. During NDJ, convection was concentrated within 5° latitude of the intertropical convergence zone (ITCZ) which was oriented east to west near the equator. December 1994 was characterized by an active phase of the intraseasonal oscillation (ISO) while January 1995 coincided with an inactive phase. Deep convective cloud was identified in IR imagery using brightness temperature (TBB) threshold techniques. Cloud forms associated with deep convection showed two distinct diurnal modes representing deep convection (TBB ≤ -60°C) and stratiform cirrus (-52°C ≤ TBB ≤ -23°C). Clouds with TBB warmer than -60°C and colder than -53°C comprised a mixed deep convection and cirrus anvil regime from the satellite's perspective with a diurnal cycle reflecting both modes of variability. The diurnal variation of cloud in these regimes was consistent for all time periods and for two tropical storms which occurred in the WP during December 1994. Based on these results and on previous studies, a -65°C cloud-top TBB threshold was chosen to isolate pixels containing active, deep convection. Spectral analysis of time series constructed from hourly cold cloud (≤ -65°C) pixel counts revealed a powerful diurnal cycle of deep convection significant at the 95% confidence level during JJA and NDJ. Composited hourly statistics of fractional areal cloud cover documented a 0500-0600 LST maximum with a 1500-1900 LST minimum of convection for both seasons. The ratio of maximum to minimum areal cold cloud coverage was greater than 2: I. A significant bi-diurnal cycle was evident in both JJA and January 1995. The bi-diurnal peak was strongest in the near-equatorial region during JJA. No semi-diurnal (spectral) peak occurred during either season. This suggests that semi-diurnal atmospheric tides do not strongly influence convection in the WP. Three objective analysis techniques were developed to analyze the relation of tropical cloud cluster structure to the daily spatial and temporal variation of deep convection. The first technique identified cold cloud intervals, called line clusters, in each image. These line clusters represented a characteristic horizontal dimension for cloud clusters of various sizes. Results showed that the diurnal cycle of convective rainfall with an early morning maximum was disproportionately dominated by the largest ~ 10% of clusters for each time period. While the number of large clusters increased only slightly throughout nocturnal hours, the area of cold cloud associated with these systems expanded dramatically. An algorithm called threshold initiation showed that all scales of organized, intensifying deep convection existed at all times of day and night. In addition, the early morning peak was composed primarily of building convection. Conditional recurrence probabilities of line clusters were computed at 24 and 48 hour intervals. Results for JJA and December 1994 revealed that when early morning convection occurred at any location, the same region contained convection the next morning nearly half the time. Convection was less likely at the 48 hour point. These results do not support diurnal theories based on sea surface heating, afternoon initiation of convection and nocturnal evolution of mesoscale convective systems. Findings indicate that the diurnal cycle of deep convective cloud is driven by the internal variation of large clusters. Clusters that exist into or form during the night, grow spatially larger and more intense. Some results support direct radiative forcing of clouds and large scale clear region radiative destabalization as possible contributors to diurnal convective variability. However, all findings are consistent with the work of Gray and colleagues that emphasizes the role of day-night variations in net tropospheric cooling in clear and longwave cooling in cloudy versus clear regions as an explanation of the observed daily variation of tropical convective rainfall.Item Open Access Earth radiation budget variability and the relationship to changes in the general circulation(Colorado State University. Libraries, 1990) Randel, David L., author; Vonder Haar, Thomas H., author; Department of Atmospheric Science, Colorado State University, publisherItem Open Access Estimation of Big Thompson flood rainfall using infrared satellite imagery(Colorado State University. Libraries, 1978) Bielicki, Dennis Eugene, author; Vonder Haar, Thomas H., author; Department of Atmospheric Science, Colorado State University, publisherItem Open Access Exploratory study for detecting low clouds (base < 10,000 feet) over the southwestern United States using Tropical Rainfall Measuring Mission Microwave (TRMM) Imager 85.5 GHz data and coincident 10.8 micron infrared data(Colorado State University. Libraries, 2001) Barlow, Stephen J., author; Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisherRecent research in retrieving cloud liquid water over land using the 85.5 GHz microwave channel has shown limited success. This work usually requires extensive manipulation of the data to correct for atmospheric effects, and to eliminate rain events Even with these corrections, the over-land methods must still address the complex spatial variability of soil and vegetation characteristics, which have a profound affect on surface emissivity, e.g., a non-uniform background. This work uses the Normalized Polarization Difference (NPD) method in an attempt to identify low cloud signature over the Southwestern United States from 1 June to 31 August 1998. This will provide nighttime capability in identifying low-cloud areas over data-sparse, data-denied regions with relatively uniform terrain characteristics. The development of a simplified method for use in data-sparse, data-denied regions was of prime importance In order to identify low clouds, effective surface emittance calculations were made using co-located Tropical Rainfall Measuring Mission Microwave 85.5 GHz data and coincident 10.8 μm infrared data for clear-sky conditions. Based on previous work, the Southwestern United States, in general, should have the large polarization differences (> 0.015) as well as uniform skin temperatures, which could provide a suitable background to detect low cloud signal above the background noise. Eleven sites were chosen based on varying degrees of polarization difference, as well as having available surface and upper air data. In situ surface observations were used to identify the low cloud base, while the infrared brightness temperature at 10. 8 μm was used to estimated the cloud top height using the nearest upper air sounding. The estimated cloud thickness was calculated from this data. Extensive efforts were made to eliminate multiple cloud layers, which would have a negative impact on brightness temperatures. A scattering index, the Grody algorithm, and surface observations were used to filter precipitating clouds. The results using a linear regression best fit indicated poor correlation (R2) between the NPD and the 2 estimated low-cloud thickness with values of R2 ranging from 0.002 to 0.345. Four primary error mechanisms were identified, and quantified. The uncorrected atmosphere accounted for about a 0.7-1.7 K error; horizontal variations in infrared temperature on the scale of 2.0-7.3 K; instrument noise of about 1.5K; and effective surface emissivity relative uncertainties ranging from 0.22- 1.16%. Future improvements in sensor noise characteristics and resolution, as well as the ability to perform instantaneous atmospheric corrections using coincident sounder and microwave imager data should lead to a viable NPD method over land.Item Open Access Final report from the Cooperative Institute for Research in the Atmosphere, Colorado State University, to the Marine Meteorology Section, Ocean Sciences Division of the Office of Naval Research on Studies of Space/Time Variability of Marine Atmospheric Boundary Layer Characteristics(Colorado State University. Libraries, 1990-08) Vonder Haar, Thomas H., author; Wetzel, Melanie A., author; Shih, Chi-Fan, author; Kuo, Hung-chi, author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisherItem Open Access Forecasting rain events in the southern Great Plains using GPS total precipitable water amounts(Colorado State University. Libraries, 2004) Meyer, Cathryn L., author; Vonder Haar, Thomas H., author; Cooperative Institute for Research in the Atmosphere (Fort Collins, Colo.), publisherItem Open Access Investigation of a remote sensing technique for droplet effective radius(Colorado State University. Libraries, 1990) Wetzel, Melanie A., author; Vonder Haar, Thomas H., author; Department of Atmospheric Science, Colorado State University, publisher