Search Results

You are looking at 1 - 10 of 24 items for

  • Author or Editor: W. May x
  • Refine by Access: All Content x
Clear All Modify Search
Fernando Caracena and Michael W. Maier

Abstract

A microburst embedded in heavy rain in a humid environment struck very near the Field Observing Site (FOS) of the Florida Area Cumulus Experiment (FACE), producing a diverging pattern of wind damage in sugar cane.

While the dry, virga-type microburst is now beginning to be understood as a result of the SAWS project, the wet, or heavy-rain-embedded, microburst still remains a mystery. The fortuitous occurrence of a wet microburst in a humid environment, with a well-marked wind damage pattern and a well-instrumented site (including upper-air soundings), furnishes a means of gleaning some understanding of the larger-scale processes that are conducive to strong downdrafts in wet environments. In this case several features were present: 1) an elevated dry layer (above 500 mb), 2) overlying a nearly moist adiabatic lower tropospheric layer (below 500 mb), 3) a short-wave trough approaching the area from the north-northeast along the western side of a synoptic-scale trough with 4) increased shear in the lower troposphere, and 5) strong boundary-layer forcing, first by a lake breeze front off Lake Okeechobee, then by convective gust fronts. The site of the microburst itself was in the portion of the storm where a new cell was initiated by a strong gust front in an area where rain was still failing from an older, dissipating cell. The strong boundary-layer forcing may have generated an impulsive updraft surge in a very wet environment with lingering precipitation, which was followed by an impulsive collapse in a water-loaded downdraft. In this case, however, the negative buoyancy due to water loading was an order of magnitude less than that due to evaporation.

Full access
Launa M. Maier, E. Philip Krider, and Michael W. Maier

Abstract

Data derived from a large network of electric field mills have been used to determine the average diurnal variation of lightning in a Florida seacoast environment. These data were obtained at the NASA Kennedy Space Center (KSC) and the Cape Canaveral Air Force Station (CCAFS) during the summers of 1976–78 and 1980 and they show a peak in lightning activity between the hours of 2000 and 2100 GMT or about 3 hours after local solar noon. When the statistics of lightning am compared with the statisfies or thunder on the same day, good agreement is round between the start times and the times of peak activity; however, the thunder stop times tend to Rag the lightning by 1 to 2 hours.

The average diurnal variation of cloud-to-ground lightning that was recorded by a network of magnetic diffusion-finders covering the entire South Florida region during the summer of 1978 is in good agreement with the results obtained at KSC and CCAFS and agrees with previous estimates of the time variations in rainfall and the rainfall rate over South Florida. The South Florida lightning data also show substantially less diurnal variation over the Atlantic Ocean and Gulf of Mexico than over the land. The implications of these results for the detection of lightning at local midnight dawn and dusk by a DMSP (Defense Meteorological Satellite Program) satellite are discussed.

Full access
P. Speth, W. May, and R. A. Madden

Abstract

No abstract available.

Full access
Ronald L. Holle and Michael W. Maier

Abstract

A tornado observed on 15 June 1973 in the FACE surface mesonetwork was studied on the mesoscale and cloud scale. Downdrafts from two preexisting cumulonimbi, initially 80 km apart, met along a north-south line in the center of the mesonet 30 min before tornado formation. Fed by the convergence of flow from the outflows of the predecessor cumulonimbi, a line of deep cumuli formed and developed rapidly. A tornado was observed as it dropped from this cumulus line. When the tornado dissipated 10 min later, heavy precipitation was reaching the surface and new outflow began to spread from the now vigorous cumulonimbus that had spawned the tornado. The life cycle of the tornado and a period of 90 rain surrounding its occurrence studied in detail from observed surface winds, radar reflectivity and surface rain gage data. The evolution of the parent cloud and tornado in a tropical thermodynamic environment with local forcing, weak shear and winds, and a potentially unstable sounding contrasts with the conditions that accompany large-scale forcing of the parent clouds in which extratropical tornadoes are found. The 850–200 mb wind shear of <2 m s−1 was the weakest found over many summers of FACE at Miami and was the only unique environmental parameter detectable on the day when the tornado formed. The similarity of the 15 June FACE tornado to Florida waterspout life cycles is noted.

Full access
Sebastian W. Hoch, C. David Whiteman, and Bernhard Mayer

Abstract

The Monte Carlo code for the physically correct tracing of photons in cloudy atmospheres (MYSTIC) three-dimensional radiative transfer model was used in a parametric study to determine the strength of longwave radiative heating and cooling in atmospheres enclosed in idealized valleys and basins. The parameters investigated included valley or basin shape, width, and near-surface temperature contrasts. These parameters were varied for three different representative atmospheric temperature profiles for different times of day. As a result of counterradiation from surrounding terrain, nighttime longwave radiative cooling in topographic depressions was generally weaker than over flat terrain. In the center of basins or valleys with widths exceeding 2 km, cooling rates quickly approached those over flat terrain, whereas the cooling averaged over the entire depression volume was still greatly reduced. Valley or basin shape had less influence on cooling rates than did valley width. Strong temperature gradients near the surface associated with nighttime inversion and daytime superadiabatic layers over the slopes significantly increased longwave radiative cooling and heating rates. Local rates of longwave radiative heating ranged between −30 (i.e., cooling) and 90 K day−1. The effects of the near-surface temperature gradients extended tens of meters into the overlying atmospheres. In small basins, the strong influence of nocturnal near-surface temperature inversions could lead to cooling rates exceeding those over flat plains. To investigate the relative role of longwave radiative cooling on total nighttime cooling in a basin, simulations were conducted for Arizona’s Meteor Crater using observed atmospheric profiles and realistic topography. Longwave radiative cooling accounted for nearly 30% of the total nighttime cooling observed in the Meteor Crater during a calm October night.

Full access
D. J. Musil, E. L. May, P. L. Smith Jr., and W. R. Sand

Abstract

Precipitation particle sizes were measured using a continuous hydrometeor sampler (foil impactor) during penetrations of hailstorms with an armored T-28 aircraft. Data have been analyzed from three penetrations of a storm near Raymer, Colorado, on 9 July 1973 at altitudes between 5.5 and 7.2 km MSL, which correspond to temperatures between about −2°C and −12°C. Other results pertinent to the Raymer storm are discussed in Parts I,II,III and elsewhere in this issue.

Most of the particles were identified as ice particles or ones containing both ice and water; however, significant amounts of liquid particles were found in the updrafts of developing cells at temperatures as cold as −12°C. Particles larger than 5 mm in diameter were typically found along the edges of the updrafts, with the precipitation concentrations being strongly dependent on these larger particles. The downdrafts were composed of ice particles.

Several particle size distributions from one of the penetrations were examined. The distributions are roughly exponential, or bi-exponential when large particles are present.

Full access
T. M. Dillon, J. A. Barth, A. Y. Erofeev, G. H. May, and H. W. Wijesekera

Abstract

A new high-frequency turbulence measuring instrument, MicroSoar, has been developed, tested, and used to make scalar variance dissipation rate measurements. MicroSoar was mounted on the undercarriage of SeaSoar, a depth-programmable winged platform, and towed by a ship, at speeds up to 7 kt, in a depth range of the sea surface to 120 m. Sensors carried by MicroSoar were a fast thermistor, a pressure sensor, a microscale capillary conductivity sensor, and a three-axis accelerometer. With appropriate assumptions about the local TS relation, measurements of microscale conductivity fluctuations can often be used to directly determine temperature variance dissipation rate (χ T), the Cox number (C x), and the scalar diathermal turbulent diffusivity (K T). Compared to conventional quasi-free-fall tethered vertically profiling instruments, MicroSoar's major advantage lies in its ability to sample large fluid volumes and large geographic areas in a short time, and to provide, rapidly and simply, two-dimensional (horizontal–vertical) representations of the distribution of oceanic mixing rates.

Full access
Alison W. Grimsdell, M. Joan Alexander, Peter T. May, and Lars Hoffmann

Abstract

Atmospheric gravity waves have a major effect on atmospheric circulation, structure, and stability on a global scale. Gravity waves can be generated by convection, but in many cases it is difficult to link convection directly to a specific wave event. In this research, the authors examine an event on 12 January 2003 when convective waves were clearly generated by a period of extremely intense rainfall in the region of Darwin, Australia, during the early morning. The waves were observed by the Atmospheric Infrared Sounder (AIRS) instrument on board the Aqua satellite, and a dry version of a nonlinear, three-dimensional mesoscale cloud-resolving model is used to generate a comparable wave field. The model is forced by a spatially and temporally varying heating field obtained from a scanning radar located north of Darwin at Gunn Point. With typical cloud-resolving model studies it is generally not possible to compare the model results feature-for-feature with observations since although the model precipitation and small-scale heating may be similar to observations, they will occur at different locations and times. In this case the comparison is possible since the model is forced by the observed heating pattern. It is shown that the model output wave pattern corresponds well to the wave pattern observed by the AIRS instrument at the time of the AIRS overpass.

Full access
Mark W. Maier, Frank W. Gallagher III, Karen St. Germain, Richard Anthes, Cinzia Zuffada, Robert Menzies, Jeffrey Piepmeier, David Di Pietro, Monica M. Coakley, and Elena Adams

Abstract

Between 2014 and 2018, the NOAA Office of Systems Architecture and Advanced Planning (OSAAP) conducted the NOAA Satellite Observing System Architecture (NSOSA) study to plan the long-term future of the NOAA constellation of operational environmental satellites. This constellation of satellites (which may include space capabilities acquired in lieu of U.S. government satellites) will follow the current GOES-R and JPSS satellite programs, beginning about 2030. This was an opportunity to design a modern architecture with no preconceived notions regarding instruments, platforms, orbits, etc., but driven by user needs, new technology, and exploiting emerging space business models. In this paper we describe how the study was structured, review major results, show how observation priorities and estimated costs drove next-generation choices, and discuss important challenges for implementing the next generation of U.S. civil environmental remote sensing satellites.

Full access
Peter T. May, Thomas D. Keenan, Rod Potts, James W. Wilson, Rob Webb, Andrew Treloar, Elly Spark, Sue Lawrence, Elizabeth Ebert, John Bally, and Paul Joe

Abstract

The Sydney 2000 Olympic Games World Weather Research Programme Forecast Demonstration Project (WWRP FDP) aimed to demonstrate the utility and impact of modern nowcast systems. The project focused on the use of radar processing systems and products for nowcasting, including severe weather. The forecast problems facing the Australian Bureau of Meteorology (BoM) on these short timescales during the FDP are briefly described. The observing system is then discussed and enhancements to the network that supported the Olympic Games forecast requirements and the WWRP FDP project are outlined. In particular, issues related to radar calibration and quality control are discussed in some detail. The paper concludes with a brief discussion on the observing system requirements to meet such modern nowcast systems, areas of further development, and impacts that the FDP had on BoM nowcasting systems. The need for end-to-end design of systems from data gathering, to analysis and product generation is emphasized.

Full access