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Matthew S. Gilmore and E. Richard Toracinta

The authors surveyed 55 university departments in the United States and Canada that grant doctor of philosophy and/or master of science degrees in meteorology or the atmospheric sciences. Two-thirds of university departments responded. Survey topics included graduate student income (stipends and health insurance benefits) and mandatory costs (tuition, fees, and health insurance costs) incurred for fall 1996.

Results show that most graduate students do have funding but only one-quarter of departments indicate that health insurance benefits are provided to graduate assistants. The largest mandatory cost is typically housing, which was estimated (except for Canadian schools) with 1996 Fair Market Rent data from the U.S. Department of Housing and Urban Development. For schools not providing it, the second largest cost is typically health insurance. The smallest costs are typically tuition (waived for graduate assistants in most cases) and fees.

The difference between income and mandatory costs over a nine-month period gives an “effective income.” Evidence was found associating greater effective income with larger departments and with locations where housing costs are larger. No significant evidence was found to associate differences in effective income with city size or geographic region. The broad range in effective income between the departments suggests that some graduate programs may be much more affordable than others.

This information can aid university departments in planning budgets that keep them competitive with one another. This paper will also help prospective graduate students by raising awareness about important issues of graduate program affordability.

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E. Richard Toracinta and Edward J. Zipser

Abstract

This study presents a systematic comparison of the distributions of mesoscale convective systems (MCSs) and lightning for 19 geographical regions classified as land, ocean, or a mixture of land and ocean between 35°N and 35°S over four 3-month periods beginning in June of 1995. The 85-GHz brightness temperatures and the lightning data are from the Special Sensor Microwave Imager (SSM/I) and the Optical Transient Detector, respectively. The MCSs are defined and classified according to their 85-GHz polarization-corrected brightness temperature (PCT), and the lightning flashes are grouped into lightning clusters. In each of the four periods, the land bias among the lightning clusters is much stronger than among the MCSs. For instance, ocean regions contain only 15%–21% of the total lightning cluster population in a given period (compared with 56%–66% over land), and the majority (>80%) of the oceanic lightning clusters are weak, with few flashes. In contrast, MCSs are more evenly distributed between land and ocean regions with 37%–41% and 40%–45% occurring over the land and oceans, respectively, in a given period. In land regions, MCSs with moderate to strong ice-scattering signatures (minimum 85-GHz PCT ≤ 190 K) and lightning clusters with moderate to high flash rates (four or more flashes) are both relatively numerous, with tropical Africa typically dominating all regions in terms of ice-scattering intensity and lightning flash rates. However, the lightning–ice-scattering relationship is less clear over the oceans. Moderate to strong ice-scattering MCSs occur with far greater frequency over ocean regions than do the moderate-to-high-flash-rate clusters. In addition, the lightning flash densities and flash-to-MCS ratios computed for each region show order-of-magnitude or larger differences between land and ocean. This result suggests that, even when normalized for the intensity of 85-GHz ice scattering, a land MCS is more likely to produce lightning than is an MCS over the ocean. This fact implies differences in the ice microphysics processes between land and ocean convective storms. These differences are under active investigation.

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E. Richard Toracinta, Robert J. Oglesby, and David H. Bromwich

Abstract

Global climate simulations are conducted to examine the sensitivity of the Last Glacial Maximum (LGM) climate to prescribed sea surface temperatures (SSTs) that are modified from the Climate: Long-range Investigation, Mapping, and Prediction (CLIMAP) study. Based on the consensus from various LGM proxy data, the SSTs are cooled by 4°C uniformly in the Tropics (30°N–30°S) relative to CLIMAP, and the high-latitude sea ice extent is reduced. Compared to results from a simulation with CLIMAP SSTs, the modified LGM SSTs cause significant opposing changes in the hemispheric and regional-scale atmospheric circulation, which are most pronounced in the winter hemisphere. For instance, there is significant weakening of the midlatitude circulation and reduction of 500-hPa eddy kinetic energy and midlatitude precipitation resulting from the decreased meridional temperature gradient in the modified SST simulation. In contrast, reduced sea ice extent during the boreal winter causes increased regional baroclinicity and intensified atmospheric circulation in the western North Pacific and the North Atlantic. Cooled tropical SSTs also increase the land–ocean temperature contrast, which strengthens the Asian summer monsoon circulation. Both LGM simulations produce enhanced low-level convergence and increased precipitation along the South Pacific convergence zone (SPCZ) relative to present day, despite the cooler LGM climate. The SPCZ orientation and intensity are closely linked to the distribution of South Pacific SSTs. Comparison of surface temperature estimates from land- and ocean-based proxy data with model output suggests that uniform cooling of the tropical SSTs and modification of the high-latitude sea ice extent may be sufficient to accurately simulate the first-order characteristics of the LGM climate.

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Karen I. Mohr, Richard Toracinta, Edward J. Zipser, and Richard E. Orville

Abstract

This study examines simultaneous SSM/I and lightning data for a sample of nine mesoscale convective systems (MCS) near League City, Texas. Comparison of lightning files of varying sizes from ±2 to ±30 min revealed that the ±10-min interval representatively sampled electrical activity in mesoscale systems. The data strongly suggested that flash density was inversely correlated with 85-GHz brightness temperature. The highest negative flash densities corresponded to low (<200 K) brightness temperatures. This relationship can be attributed to the scattering of upwelling 85-GHz radiation by graupel and hail, the same large particles believed to be necessary for charge separation. Variations were found depending on the sizes of an MCSs convective regions and its stage of development. The majority of positive flashes were located in the 210–250-K range. This brightness temperature range was comparable to the brightness temperature range of trailing stratiform regions and was consistent with observations of a higher percentage of positive lightning in stratiform regions. The results of both parts of this study implied that the pattern and magnitude of brightness temperature depressions and, by extension, the amount and distribution of lightning of an MCS was related to the presence of large ice particles in the mixed-phase region of that MCS.

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E. Richard Toracinta, Karen I. Mohr, Edward J. Zipser, and Richard E. Orville

Abstract

This is the first part of a two part study. Part I compares radar data from the League City, Texas, WSR-88D and cloud-to-ground (CG) lightning data for a set of eight mesoscale convective systems (MCSs), which occur at various stages of development along the upper Texas gulf coast. Vertical profiles of radar reflectivity (VPRR) as well as plan views and vertical cross sections are constructed to characterize the structure and relative strength of each MCS. The VPRR are also compared with similar profiles from tropical oceanic MCSs.

The data show that in all the majority of negative CG lightning flashes are located near high-reflectivity convective cores (>35 dBZ) in the mixed-phase region (0°C ≤T≥ −20°C). Growing or mature MCSs typically had larger negative flash counts and higher percentages of negative lightning (≥80%) associated with convective core than MCSs at later stages of their life cycle. Comparison of the median VPRR for the various MCSs showed that although each case had high-reflectivity cores (45–55 dBZ) in the lowest 2–3 km, the more electrically active MCSs were characterized by smaller reflectivity lapse rates (decrease of reflectivity with height) in mixed-phase region than the cores in the remaining systems. Based on existing theories of charge separation, the observation of high negative flash counts coincident with convective corn having small reflectivity lapse rates in the mixed phase region is consistent with the presence of large ice particles aloft.

Positive CG flashes were mostly located in low reflectivity (less than 30 dBZ near the −10°C level) stratiform regions, independent of MCS life cycle stage or VPRR type. Several cases with reports of large hail also had high positive flash densities associated with high reflectivity cores.

Part II of this study compares 85-GHz brightness temperatures from the Special Sensor Microwave/Imager to lightning data for the same set of MCSs in Part I. Results from both parts of this study strongly suggest that the presence of large ice particles aloft is the common linkage between MCSs with lightning, with high radar reflectivity aloft, and large 85-GHz temperature depressions.

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David H. Bromwich, E. Richard Toracinta, Robert J. Oglesby, James L. Fastook, and Terence J. Hughes

Abstract

Regional climate simulations are conducted using the Polar fifth-generation Pennsylvania State University (PSU)–NCAR Mesoscale Model (MM5) with a 60-km horizontal resolution domain over North America to explore the summer climate of the Last Glacial Maximum (LGM: 21 000 calendar years ago), when much of the continent was covered by the Laurentide Ice Sheet (LIS). Output from a tailored NCAR Community Climate Model version 3 (CCM3) simulation of the LGM climate is used to provide the initial and lateral boundary conditions for Polar MM5. LGM boundary conditions include continental ice sheets, appropriate orbital forcing, reduced CO2 concentration, paleovegetation, modified sea surface temperatures, and lowered sea level.

The simulated LGM summer climate is characterized by a pronounced low-level thermal gradient along the southern margin of the LIS resulting from the juxtaposition of the cold ice sheet and adjacent warm ice-free land surface. This sharp thermal gradient anchors the midtropospheric jet stream and facilitates the development of synoptic cyclones that track over the ice sheet, some of which produce copious liquid precipitation along and south of the LIS terminus. Precipitation on the southern margin is orographically enhanced as moist southerly low-level flow (resembling a contemporary Great Plains low-level jet configuration) in advance of the cyclone is drawn up the ice sheet slope. Composites of wet and dry periods on the LIS southern margin illustrate two distinctly different atmospheric flow regimes. Given the episodic nature of the summer rain events, it may be possible to reconcile the model depiction of wet conditions on the LIS southern margin during the LGM summer with the widely accepted interpretation of aridity across the Great Plains based on geological proxy evidence.

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David H. Bromwich, E. Richard Toracinta, Helin Wei, Robert J. Oglesby, James L. Fastook, and Terence J. Hughes

Abstract

Optimized regional climate simulations are conducted using the Polar MM5, a version of the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5), with a 60-km horizontal resolution domain over North America during the Last Glacial Maximum (LGM, 21 000 calendar years ago), when much of the continent was covered by the Laurentide Ice Sheet (LIS). The objective is to describe the LGM annual cycle at high spatial resolution with an emphasis on the winter atmospheric circulation. Output from a tailored NCAR Community Climate Model version 3 (CCM3) simulation of the LGM climate is used to provide the initial and lateral boundary conditions for Polar MM5. LGM boundary conditions include continental ice sheets, appropriate orbital forcing, reduced CO2 concentration, paleovegetation, modified sea surface temperatures, and lowered sea level.

Polar MM5 produces a substantially different atmospheric response to the LGM boundary conditions than CCM3 and other recent GCM simulations. In particular, from November to April the upper-level flow is split around a blocking anticyclone over the LIS, with a northern branch over the Canadian Arctic and a southern branch impacting southern North America. The split flow pattern is most pronounced in January and transitions into a single, consolidated jet stream that migrates northward over the LIS during summer. Sensitivity experiments indicate that the winter split flow in Polar MM5 is primarily due to mechanical forcing by LIS, although model physics and resolution also contribute to the simulated flow configuration.

Polar MM5 LGM results are generally consistent with proxy climate estimates in the western United States, Alaska, and the Canadian Arctic and may help resolve some long-standing discrepancies between proxy data and previous simulations of the LGM climate.

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