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P. Ramamurthy, E. R. Pardyjak, and J. C. Klewicki

Abstract

Data obtained in downtown Oklahoma City, Oklahoma, during the Joint Urban 2003 atmospheric dispersion study have been analyzed to investigate the effects of upstream atmospheric stability on turbulence statistics in an urban core. The data presented include turbulent heat and momentum fluxes at various vertical and horizontal locations in the lower 30% of the street canyon. These data have been segregated into three broad stability classification regimes: stable (z/L > 0.2), neutral (−0.2 < z/L < 0.2), and unstable (z/L < −0.2) based on upstream measurements of the Monin–Obukhov length scale L. Most of the momentum-related turbulence statistics were insensitive to upstream atmospheric stability, while the energy-related statistics (potential temperatures and kinematic heat fluxes) were more sensitive. In particular, the local turbulence intensity inside the street canyon varied little with atmospheric stability but always had large magnitudes. Measurements of turbulent momentum fluxes indicate the existence of regions of upward transport of high horizontal momentum fluid near the ground that is associated with low-level jet structures for all stabilities. The turbulent kinetic energy normalized by a local shear stress velocity collapses the data well and shows a clear repeatable pattern that appears to be stability invariant. The magnitude of the normalized turbulent kinetic energy increases rapidly as the ground is approached. This behavior is a result of a much more rapid drop in the correlation between the horizontal and vertical velocities than in the velocity variances. This lack of correlation in the turbulent momentum fluxes is consistent with previous work in the literature. It was also observed that the mean potential temperatures almost always decrease with increasing height in the street canyon and that the vertical heat fluxes are always positive regardless of upstream atmospheric stability. In addition, mean potential temperature profiles are slightly more unstable during the unstable periods than during the neutral or stable periods. The magnitudes of all three components of the heat flux and the variability of the heat fluxes decrease with increasing atmospheric stability. In addition, the cross-canyon and along-canyon heat fluxes are as large as the vertical component of the heat fluxes in the lower portion of the canyon.

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Mohan K. Ramamurthy, Robert M. Rauber, Brian P. Collins, and Naresh K. Malhotra

Abstract

Two large-amplitude gravity waves were observed over the midwestern United States on 5 and 14 January 1989 during the University of Illinois Winter Precipitation Program. On both days, an extensive amount of data was recorded, including data from two radars and a radiosonde facility. The waves originated near Missouri, registered pressure fluctuations as large as 10 mb, and produced distinct precipitation bands along their updraft regions.

The waves were long-lived and maintained their identity over 1000 km, a distance several times their wave-lengths. The synoptic features at the surface were dissimilar. A deep cyclone was present on 5 January, while a leeside trough was present on 14 January. However, the middle- and upper-tropospheric flow patterns were similar. In both cases, the axis of a trough was immediately upstream of the gravity-wave genesis area and a jet streak had just propagated through the base of the trough toward a downstream ridge. Soundings taken near the gravity waves were remarkably similar, with both soundings showing a surface inversion capped by a deep layer of near-neutral stability. However, the relationship between the location of the gravity wave and the region of large-scale precipitation differed in the two cases. The 5 January wave occurred at the back edge of the precipitation associated with a comma cloud, while the wave on 14 January was observed at the leading edge of the synoptic-scale precipitation region.

The gravity wave had the structure of a solitary wave of elevation on 5 January, while it appeared as an undular bore with an embedded pressure jump on 14 January. A critical level, with small Richardson numbers, was present in both the cases. A well-defined duct, formed by an inversion below and critical level above, contributed to the maintenance of waves. Shearing instability and geostrophic adjustment were the likely generation mechanisms, though it was difficult to discount the role of convection.

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Mohan K. Ramamurthy, Kenneth P. Bowman, Brian F. Jewett, John G. Kemp, and Charles Kline

Over the past several years, the Department of Atmospheric Sciences at the University of Illinois has developed a computerized weather laboratory that permits interactive access to real-time data from observing sites around the United States and to output from numerical weather prediction models at the operational centers. Such a setup, with timely access to observations and numerical model forecasts from any networked terminal, personal computer, or workstation, is a valuable tool for education and research in meteorology. The University of Illinois system acts as a real-time, on-line, in-class instructional meteorology laboratory for students. The data-display software is based on the X-windows protocol, which is network transparent and system independent.

In addition to software packages distributed by the University Data Project (UNIDATA), software tools developed by the National Center for Supercomputing Applications and the University of Illinois are used to display, animate, and manipulate conventional maps, satellite images, and radar summaries. The underlying idea is to bring every product from a traditional synoptic laboratory to any desktop computer residing on the network.

An overview of the University of Illinois prototype for a paperless, desktop synoptic lab, together with the details of the hardware and software involved, is presented here, along with some examples of its use in teaching and research.

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Mohan K. Ramamurthy, Robert M. Rauber, Brian P. Collins, Michael T. Shields, Patrick C. Kennedy, and Wallace L. Clark

To obtain a better understanding of the role of synoptic-scale disturbances in organizing mesoscale precipitation in the midwestern United States during the winter season, and to address scientific issues regarding mesoscale dynamics of winter storms, the University of Illinois Winter Precipitation Program was conducted over a period of three winters between 1988 and 1990. The observing systems included a 10-cm wavelength meteorological Doppler radar operated by the Illinois State Water Survey, the Flatland 6-m wind profiler operated by the NOAA Aeronomy Laboratory, and an NCAR Cross-chain Loran Atmospheric Sounding System. In all, 26 storms were observed during the 3-year period. The associated precipitation ranged from highly convective storms in the warm sector to stratified clouds containing organized banded structure within the occlusion. The principle dynamical mechanisms at work often varied widely from one storm to another and sometimes within a storm. This article describes the goals and objectives of the project, as well as a few selected observations and some preliminary findings from the data gathered.

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R. E. Pandya, D. R. Smith, M. K. Ramamurthy, P. J. Croft, M. J. Hayes, K. A. Murphy, J. D. McDonnell, R. M. Johnson, and H. A. Friedman

The 11th American Meteorological Society (AMS) Education Symposium was held from 13 to 15 January 2002 in Orlando, Florida, as part of the 82nd Annual Meeting of the AMS. The theme of the symposium was “creating opportunities in educational outreach in the atmospheric and related sciences.” Drawing from traditional strengths in meteorology and numerous national recommendations, the presentations and posters of the symposium highlighted three opportunities for reform. These opportunities build on partnerships between diverse educational stakeholders, efforts to make science education more like scientific practice, and strategies that place the atmospheric sciences within a larger, multidisciplinary context that includes oceanography, hydrology, and earth-system science.

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N. Hosannah, J. González, R. Rodriguez-Solis, H. Parsiani, F. Moshary, L. Aponte, R. Armstrong, E. Harmsen, P. Ramamurthy, M. Angeles, L. León, N. Ramírez, D. Niyogi, and B. Bornstein

Abstract

Modulated by global-, continental-, regional-, and local-scale processes, convective precipitation in coastal tropical regions is paramount in maintaining the ecological balance and socioeconomic health within them. The western coast of the Caribbean island of Puerto Rico is ideal for observing local convective dynamics as interactions between complex processes involving orography, surface heating, land cover, and sea-breeze–trade wind convergence influence different rainfall climatologies across the island. A multiseason observational effort entitled the Convection, Aerosol, and Synoptic-Effects in the Tropics (CAST) experiment was undertaken using Puerto Rico as a test case, to improve the understanding of island-scale processes and their effects on precipitation. Puerto Rico has a wide network of observational instruments, including ground weather stations, soil moisture sensors, a Next Generation Weather Radar (NEXRAD), twice-daily radiosonde launches, and Aerosol Robotic Network (AERONET) sunphotometers. To achieve the goals of CAST, researchers from multiple institutions supplemented existing observational networks with additional radiosonde launches, three high-resolution radars, continuous ceilometer monitoring, and air sampling in western Puerto Rico to monitor convective precipitation events. Observations during three CAST measurement phases (22 June–10 July 2015, 6–22 February 2016, and 24 April–7 May 2016) captured the most extreme drought in recent history (summer 2015), in addition to anomalously wet early rainfall and dry-season (2016) phases. This short article presents an overview of CAST along with selected campaign data.

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