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Atmospheric sciences senior section.

* Adegoke, J. and K.P. Gallo. Department of Geosciences. University of Missouri-Kansas City. A Multi-Sensor Approcach To Estimating Global Urban Heal Island Signature. Major urban centers and their metropolitan areas affect the local and regional climate by altering the surface heat, moisture. momentum and gas exchanges between the land surface and the lowest 1-2 km of the atmosphere. With the changes in the character of natural landscape that result from the city-building process, a greater proportion of incoming solar energy is absorbed into paved surfaces and rooftops, Here we present a method for estimating UHI effects on a global temperature data set and provide guidance on urban heat-island influence temperature adjustments for stations included in global climatological data networks. The method is based on satellite-derived normalized difference vegetation index (NDVI) sampled during the warm season months over urban and rural regions composed of a variety of land surface environments.

We use the following globally available. satellite derived, data sets: a global 1-km AVHRR -derived NDVI 10-day composite data, a global DMSP-OLS city lights data, and the IGBP global 1-km land cover data set.

The mean estimated temperature difference between Northern Hemisphere stations identified as urban based on local and regional differences in observed NDVI, and their surrounding rural environment, ranged from 0.69[degrees]C for September of 1992 to 0.98[degrees]C for August of 1993. Over the warm-season months examined the mean estimated temperature differences were 0.90[degrees]C (stations identified as urban) and 0.19[degrees]C (stations classified as rural). The maximum estimated temperature difference between an urban station and its surrounding environment ranged from 2.03[degrees]C (October 1992) to 3.2[degrees]C (August 1993). These differences were statistically significant (p = .01) for those stations identified as urban, for each month examined. Significant differences were also observed for those stations identified as rural, based on the NDVI thresholds, for each of the months examined. The local samples associated with the rural stations were found to have significantly greater temperature values than the regional samples. Exceptions were observed, most notably in desert environments where the local samples occasionally displayed greater NDVI values than the surrounding environments. Differences in local and regional NDVI were also significant for all months for both the urban and rural sets of stations. The observed differences in NDVI and estimated temperature between local and regional samples of stations classified as urban were anticipated. The uniqueness of this study is the demonstrated value of satellite-derived datasets for estimating the UHI influence on a global basis. On going work includes an assessment of the impact of those results on the current data sets used to estimate regional and global temperatures.

Akyuz, F. A. (1), * Lack, S. A. (1), Mike Palecki (2). Atmospheric Science Program, University of Missouri-Columbia (1), Midwestern Regional Climate Center (2). Variation Of Peak Wind Speed With Averaging Time. The U.S. Weather Bureau and the successor National Weather Service have reported peal< wind speeds with a variety of averaging periods. Prior to 1964, the Local Climatological Data (LCD) publication reported the peak wind speeds averaged over 1 hour. From 1965 to August 1989 the publication adopted the fastest-mile wind definition, which is the time it takes for 1 mile of wind to pass through the anemometer. This can be thought of as effectively a peak wind averaged over a variable range of period lengths, depending on how long it took for the mile of wind to pass the instrument. Starting in September 1989 and continuing through 1994, LCDs reported the fastest-minute wind, which is averaged over a 1-minute period. Finally, from the advent of ASOS in 1995 to the present, the peak wind speed has been reported in terms of both 5-second and 2-minute winds. If one is interested in comparing peak winds or processing a peak-wind-climatology for a period spanning current to pre-1964 data, a standard averaging period must be developed to facilitate these activities. This paper addresses a joint project between Midwestern Regional Climate Center, National Climatic Data Center and Missouri Climate Center to make operational a simple algorithm that converts peak wind speeds observed using one averaging period to an averaging period chosen by the user. A Web interface will receive the input peak wind speed and known averaging period and request the desired output wind-speed averaging period. The algorithm will make the conversion based on a study by Durst (1960), who developed a statistical relationship between 1-hour peak wind and the wind speed of various averaging periods. The algorithm will also convert the fastest mile wind to other averaging periods.

* Alabi, O. Department of Geosciences, University of Missouri-Kansas City. Validation Of Trmm Satellite Data Over Nigeria. This study investigated rain bearing convective systems over Nigeria, a region in the tropics bounded by latitudes 4[degrees]N-14[degrees]N and Longitudes 3[degrees]E-14[degrees]E, using conventional and satellite derived precipitation data. The period of study was 1998, with special emphasis on the month of July when Nigeria normally falls within the most convectively active zones in the West African region. Tropical Rainfall Measuring Mission (TRMM) satellite derived rainfall over Nigeria was compared with rain gauge measurements obtained at 31 meteorological stations located within the country. The agreement between the two sets of data varied between 31% and 97%. The disparity in rainfall amounts, which was greatest for the months of June to September, especially at the inland stations, was attributed to the inability of the TRMM satellite to capture the super cells in the numerous cloud clusters that were prevalent over the region during these months of the year. These super cells, clearly identifiable on METEOSAT visible imagery, were found to be almost stationary and randomly distributed within the cluster. They were not uniformly arranged as in the case of fast moving squall lines. Such systems, which were short live& produced very heavy precipitation. The TRMM satellite, due to its low frequency of observation did not detect these.

* Guinan, P.E., W.L. Decker, and A.R. Lupo. Department of Soil, Environmental, and Atmospheric Science, University of Missouri-Columbia. Using Seasonal And Weekly Precipitation Patterns To Predict The Probability Of Summer Drought And The Effects On Crop Yields Over Northwestern Missouri. This study is an examination of weekly precipitation records and annual crop yield data for USDA crop reporting district one (CRD 1) in northwestern Missouri. Weekly precipitation data were collected for the period 1919-2002, and crop yield data for corn and soybeans were gathered between 1920-2002 and 1944-2002, respectively. Regression analyses using 1990's crop technology were applied to the corn and soybean yield data in order to eliminate yield bias due to the introduction of fertilizer and improved hybrids. Antecedent precipitation periods for autumn, spring, and summer were analyzed each year and compared to the corn and soybean yields of that year. Contingency tables were constructed comparing precipitation periods to yields and divided into 5 categories. Probability statements predicting the likelihood of summer agricultural drought and yield potential were developed.

* Kunz, A. R., and A. R. Lupo. Department of Soil, Environmental, and Atmospheric Sciencel, University of Missouri--Columbia. The Role Of The Planetary-Scale Flow Regime In The May 2003 Tornado Outbreaks: How Unusual Was The Situation? During the last few years, two studies have explored the role of the planetary-scale in contributing to devastating synoptic and mesoscale events. These studies have shown that the planetary-scale can play a critical role in providing a favorable background for the occurrence of the smaller-scale events. This study examined the role of the planetary-scale in providing a favorable background for the May 2003 tornado outbreaks. We demonstrate that simultaneous blocking events in the Eastern Pacific and Western Atlantic regions maintained an active jet stream and stationary front across the southern portion of the North American continent. This front was the boundary between a large-scale region of cold air to the north and warm humid air to the south. This scenario was maintained by the two blocking events, and provided a favorable background for the occurrence of at least three rapidly successive severe weather outbreaks during the first ten days of May 2003. These blocking events then decayed as the planetary-scale background flow regime transitioned from one balanced state to another. After the breakdown of the planetary-scale flow pattern, the background was no longer favorable for the continued occurrence of severe weather. Additionally, it was found that simultaneously occurring blocking events such as these are not uncommon occurrences in the Northern Hemisphere flow pattern. Thus, it is reasonable to assume that severe weather outbreaks such as the May 2003 event are not unprecedented even if such an event has not been documented during the last 50 years.

Podzimek, J. Cloud and Aerosol Sciences Laboratory, University of Missouri-Rolls. Contribution To The Micrphyscial And Meteorological Explanation Of Measured Dimensional Parameters Of Columnar Snow Crystals. The concentrations and shapes of snow crystals in the ground air layer are important for the description of the precipitation and for the investigation of radiative transfer processes and visibility. In this paper are summarized the main results of columnar crystal concentration measurements during several years at Groveland, IL, and determined the prevailing crystal size distributions. Microscopical evaluation of 738 columnar crystals included their main dimensions (lengths and widths) and the detailed description of their shapes. The main conclusion of this investigation was that the simple exponential relationship between the two main axes holds approximately for most of the evaluated crystals. However, e.g. for short columns, collected at ground air temperatures below -16 [degrees]C, the observed axes rations (c/a) were in mean 37% larger than those calculated according to the parameters published by other investigators. The remarkable temperature dependence of snow crystal habits (primary crystal growth) and the modification of the crystal shapes by the water vapor distribution in the immediate vicinity of the surfaces of falling columnar crystals (secondary crystal growth) is discussed in more detail.

Podzimek, J. Cloud and Aerosol Sciences Laboratory, University of Missouri-Rolls. Composition And Dimensional Parameters Of The Main Snowflake Types. The main types and size distributions of snowflakes collected at the ground in the Midwestern USA during the years 1998-2002 were described by Podzimek and Market (2004). This contribution brings into focus more detailed analysis of the composition of snowflakes in the first five groups of the suggested seven classes of snow element aggregates. Included are needles, sheaths, small columnar and planar crystals, medium size stellar and planar crystals and large dendritic crystals. Mean percentages of different snow crystals in each group are mentioned, because usually each snowflake represents a mixture of different snow crystals with one dominant crystal type. During several snowfalls in December 2003 were evaluated the maximal size and approximate width of each snowflake replica for determining its asymmetry. The snowflake asymmetries are changing considerably during a snowfall and are strongly affected by the interaction of snow crystals from different levels in a cloud system and by meteorological conditions in the ground air layer. It is shown how the presence of large dendritic and stellar crystals, of needles and of deposited minigraupels modifies strongly the snowflake asymmetry.

* Silberberg, S.R. NOAA/NWS/NCEP/ Aviation Weather Center. Accuracy Of Global Model Thunderstorm Forecasts. Global model thunderstorm forecasts are used as guidance by aviation forecasters to prepare worldwide 24 h forecasts of thunderstorm height and location. The accuracy of global model thunderstorm forecasts affects the forecast process and the accuracy of issued aviation thunderstorm forecasts. These forecasts are used by world airlines for route planning and fuel load management on all international routes. Global model thunderstorm 24 h forecasts are verified four times a day by global composite satellite imagery, which has been processed to show active thunderstorms. Model forecasts are 70% accurate over the tropical Atlantic, Pacific, and Indian Oceans and 30% accurate over the continents such as Australia, South America, and Africa. Based on these results, the Aviation Weather Center is revising procedures for forecasting convection over Australia, South America, and Africa and the global oceans. In addition, poor model thunderstorm forecasts reduce the accuracy of model forecasts of jet streams and storm systems, which in turn, reduce the accuracy of short-range and long-range public forecasts.

* Tilly, D.E., A.R. Lupo, and C.J. Melick. Department of Soil, Environmental, and Atmospheric Science, University of Missouri-Columbia. Calculated Vertical Motions In A Southern Hemisphere Blocking And Cyclone Event. In this study, several methods were used to calculate vertical motions in a Southern Hemisphere blocking and cyclone event, which occurred during a 48 hour period beginning with 1200 UTC 28 July 1986. The results were then compared to the vertical motions provided with the National Centers for Environmental Prediction (NCEP) re-analyses. The vertical motions were calculated using the kinematic method and the Omega Equation. In order to use the kinematic method, several numerical methods for the integration were tested, including the trapezoidal method and Simpson's Rule. Second and fourth-order finite differencing were used to calculate horizontal divergence. These results demonstrated that the vertical motions were similar for the two finite differencing methods, and that the Simpson's Rule integrations produced the most robust vertical motions. Several forms of the Omega Equation were used including the use of Q-vectors, and the Q-G, Extended (diabatic processes included), and Full versions of the Omega Equations. Each of these forms used fourth order finite differencing to calculate derivative quantities, and to invert the laplacian quantity on the left-hand-side of the equation. The Q-vector form produced the smoothest pattern which was similar to the NCEP and Kinematic Omegas. The Full Omega equation produced the most robust vertical motions, however, the results using the Full and Extended Omega Equations were similar. These results demonstrate that most methodologies were adequate for estimating vertical motions for use as a diagnostic in SH synoptic events.

* Zuki, Z.M., and A.R. Lupo. Department of Soil, Environmental, and Atmospheric Science, University of Missouri-Columbia. Interaunual Variability Of Tropical Cyclone In The Southern South China Sea. A study of the variability of tropical cyclones (TC) activity in the southern South China Sea (south of 10 degrees North), which is part of the West North Pacific basin, was carried out during a 44 year period (1960-2003). Fewer studies have done in this region compared to the West North Pacific and South China Sea itself. The initial results of this study shows that only 3.3 percent of the total of TC (tropical depression, tropical storm and typhoon) activity in the West North Pacific basin occurred in this area during the period of study. The trend of the TC activities in this region over the past years and correlation with the large scale phenomena like El-Nino-Southcrn Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) will be studied. Further results showed that there were fewer TC activities in this region during El-Nino year compare to the La-Nina and neutral year. These results also show that roughly half of the TC activities in this area were of local origin. Analysis of a time series for monthly mean Sea Level Pressure (SLP), Sea Surface Temperature (SST) and steering wind over this area also will be examined in order to find any correlation with the variability of TC activity in this region.

Patrick S. Market

University of Missouri--Columbia
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Title Annotation:Collegiate & Senior Divisions
Author:Market, Patrick S.
Publication:Transactions of the Missouri Academy of Science
Geographic Code:1U4MO
Date:Jan 1, 2004
Words:2542
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