Steven M. Lazarus

Mesowest: Cooperative Mesonets in the Western United States

Abstract Meteorological data from over 2800 automated environmental monitoring stations in the western United States are collected, processed, archived, integrated, and disseminated as part of the MesoWest program. MesoWest depends upon voluntary access to provisional observations from environmental monitoring stations installed and maintained byfederal, state, and local agencies and commercial firms. In many cases, collection and transmission of these observations are facilitated by NWS forecast offices, government laboratories, and universities. MesoWest augments the Automated Surface Observing System (ASOS) network maintained by the NWS, Federal Aviation Administration, and Department of Defense. MesoWest increases the coverage of observations in remote locations and helps capture many of the localand mesoscale weather phenomena that impact the public. The primary goal of MesoWest is to improve timely access to automated observations for NWS forecasters at offices throughout the western United States. ...

The Influence of Helicity on Numerically Simulated Convective Storms

Abstract A three-dimensional numerical cloud model is used to investigate the influence of storm-relative environmental helicity (SREH) on convective storm structure and evolution, with a particular emphasis on the identification of ambient shear profiles that are conducive to the development of long-lived, strongly rotating storms. Eleven numerical simulations are made in which the depth and turning angle of the ambient vertical shear vector are varied systematically while maintaining a constant magnitude of the shear in the shear layer. In this manner, an attempt is made to isolate the effects of different environmental Felicities on storm morphology and show that the SREH and bulk Richardson number, rather than the mean shear in the low levels, determine the rotational characteristics and morphology of deep convection. The results demonstrate that storms forming in environments characterized by large SREH are longer-lived than those in less helical surroundings. Further, it appears that the storm-relat...

A Cloud Climatology of the Southern Great Plains ARM CART

Abstract Cloud amount statistics from three different sources were processed and compared. Surface observations from a National Centers for Environmental Prediction dataset were used. The data (Edited Cloud Report; ECR) consist of synoptic weather reports that have been edited to facilitate cloud analysis. Two stations near the Southern Great Plains (SGP) Cloud and Radiation Test Bed (CART) in north-central Oklahoma (Oklahoma City, Oklahoma and Wichita, Kansas) were selected. The ECR data span a 10-yr period from December 1981 to November 1991. The International Satellite Cloud Climatology Project (ISCCP) provided cloud amounts over the SGP CART for an 8-yr period (1983–91). Cloud amounts were also obtained from Micro Pulse Lidar (MPL) and Belfort Ceilometer (BLC) cloud-base height measurements made at the SGP CART over a 1-yr period. The annual and diurnal cycles of cloud amount as a function of cloud height and type were analyzed. The three datasets closely agree for total cloud amount. Good agreement w...

A MODIS Sea Surface Temperature Composite for Regional Applications

Sea surface temperature (SST) is an important input for regional and global weather modeling, but timely high- resolution SST data from either in situ or satellite sources are limited. A regional near-real-time aqua moderate resolution imaging spectroradiometer (MODIS) 1-km-resolution SST composite has been developed by the NASA Short-term Prediction and Research Transition (SPoRT) program to provide continuous high-resolution SST fields twice daily for regional weather applications. The SPoRT Aqua MODIS SST composite is inter- compared to both half-degree-resolution real-time global (RTG) SST analysis and a 6-km-resolution geostationary operational environmental satellite 12 (GOES) Imager SST analysis and validated against buoy data for the month of May 2004. The SPoRT MODIS composite provides more accurate and detailed spatial information than the RTG-SST or GOES products during this period. Compared to limited buoy data, the daytime MODIS composites for May 2004 were found to have an average cool bias of -0.09degC, and the nighttime composites an average cool bias of -0.29degC, with both day and night composites having correlation values of approximately 0.90. A comparison of the MODIS SST composite to the more recent and higher resolution 12th-degree RTG-SST analysis and the 20th-degree resolution operational sea surface temperature and sea ice analysis indicated that the SPoRT MODIS composite provides additional spatial and diurnal cycle information on a regional scale.

The rarity of terrestrial gamma‐ray flashes

We report on the first search for Terrestrial Gamma-ray Flashes (TGFs) from altitudes where they are thought to be produced. The Airborne Detector for Energetic Lightning Emissions (ADELE), an array of gamma-ray detectors, was flown near the tops of Florida thunderstorms in August/September 2009. The plane passed within 10 km horizontal distance of 1213 lightning discharges and only once detected a TGF. If these discharges had produced TGFs of the same intensity as those seen from space, every one should have been seen by ADELE. Separate and significant nondetections are established for intracloud lightning, negative cloud-to-ground lightning, and narrow bipolar events. We conclude that TGFs are not a primary triggering mechanism for lightning. We estimate the TGF-to-flash ratio to be on the order of 10^(−2) to 10^(−3) and show that TGF intensities cannot follow the well-known power-law distribution seen in earthquakes and solar flares, due to our limits on the presence of faint events.

Near-Real-Time Applications of a Mesoscale Analysis System to Complex Terrain

Abstract Several mesoscale data analysis systems are reviewed, of which one is then adapted and applied to the complex terrain of northwest Utah and the western United States. The analysis system relies on the simple, but computationally efficient, successive correction methodology. Near-real-time three-dimensional mesoscale analyses are produced hourly over northwest Utah at 1-km horizontal resolution while analyses are produced every 15 min for surface fields over northwest Utah and the western United States. Surface analyses over the western United States are also generated at 0000 and 1200 UTC to help to initialize 36-h mesoscale model forecasts. Comparisons between the 1-km three-dimensional analyses and the background three-dimensional analysis provided by the National Centers for Environmental Prediction Rapid Update Cycle, version 2 (RUC-2), indicate that, where surface and upper-air observations are abundant, the local analysis adds information beyond that of simply interpolating the background (...

A terrestrial gamma ray flash observed from an aircraft

On 21 August 2009, the Airborne Detector for Energetic Lightning Emissions (ADELE), an array of six gamma-ray detectors, detected a brief burst of gamma rays while flying aboard a Gulfstream V jet near two active thunderstorm cells. The duration and spectral characteristics of the event are consistent with the terrestrial gamma ray flashes (TGFs) seen by instruments in low Earth orbit. A long-duration, complex +IC flash was taking place in the nearer cell at the same time, at a distance of ~10 km from the plane. The sferics that are probably associated with this flash extended over 54 ms and included several ULF pulses corresponding to charge moment changes of up to 30 C km, this value being in the lower half of the range of sferics associated with TGFs seen from space. Monte Carlo simulations of gamma ray propagation in the Earths atmosphere show that a TGF of normal intensity would, at this distance, have produced a gamma ray signal in ADELE of approximately the size and spectrum that was actually observed. We conclude that this was the first detection of a TGF from an aircraft. We show that because of the distance, ADELEs directional and spectral capabilities could not strongly constrain the source altitude of the TGF but that such constraints would be possible for TGFs detected at closer range.

The Impact of High-Resolution Sea Surface Temperatures on the Simulated Nocturnal Florida Marine Boundary Layer

Abstract High- and low-resolution sea surface temperature (SST) analysis products are used to initialize the Weather Research and Forecasting (WRF) Model for May 2004 for short-term forecasts over Florida and surrounding waters. Initial and boundary conditions for the simulations were provided by a combination of observations, large-scale model output, and analysis products. The impact of using a 1-km Moderate Resolution Imaging Spectroradiometer (MODIS) SST composite on subsequent evolution of the marine atmospheric boundary layer (MABL) is assessed through simulation comparisons and limited validation. Model results are presented for individual simulations, as well as for aggregates of easterly- and westerly-dominated low-level flows. The simulation comparisons show that the use of MODIS SST composites results in enhanced convergence zones, earlier and more intense horizontal convective rolls, and an increase in precipitation as well as a change in precipitation location. Validation of 10-m winds with b...

No barrier to emergence of bathyal king crabs on the Antarctic shelf

Significance For tens of millions of years, cold conditions have excluded shell-crushing fish and crustaceans from the continental shelf surrounding Antarctica. Rapid warming is now allowing predatory crustaceans to return. Our study of the continental slope off the western Antarctic Peninsula showed that abundant, predatory king crabs comprise a reproductively viable population at 841- to 2,266-m depth. Depth profiles of temperature, salinity, habitat structure, food availability, and predators indicate that there are no barriers to prevent king crabs from moving upward onto the outer shelf at 400–550 m. A cold-water barrier above 200 m could be breached within the next few decades. Emergence of king crabs on the shelf could have catastrophic consequences for the unique seafloor communities of Antarctica. Cold-water conditions have excluded durophagous (skeleton-breaking) predators from the Antarctic seafloor for millions of years. Rapidly warming seas off the western Antarctic Peninsula could now facilitate their return to the continental shelf, with profound consequences for the endemic fauna. Among the likely first arrivals are king crabs (Lithodidae), which were discovered recently on the adjacent continental slope. During the austral summer of 2010‒2011, we used underwater imagery to survey a slope-dwelling population of the lithodid Paralomis birsteini off Marguerite Bay, western Antarctic Peninsula for environmental or trophic impediments to shoreward expansion. The population density averaged ∼4.5 individuals × 1,000 m−2 within a depth range of 1,100‒1,500 m (overall observed depth range 841–2,266 m). Images of juveniles, discarded molts, and precopulatory behavior, as well as gravid females in a trapping study, suggested a reproductively viable population on the slope. At the time of the survey, there was no thermal barrier to prevent the lithodids from expanding upward and emerging on the outer shelf (400- to 550-m depth); however, near-surface temperatures remained too cold for them to survive in inner-shelf and coastal environments (<200 m). Ambient salinity, composition of the substrate, and the depth distribution of potential predators likewise indicated no barriers to expansion of lithodids onto the outer shelf. Primary food resources for lithodids—echinoderms and mollusks—were abundant on the upper slope (550–800 m) and outer shelf. As sea temperatures continue to rise, lithodids will likely play an increasingly important role in the trophic structure of subtidal communities closer to shore.

Local Adjustment of the Background Error Correlation for Surface Analyses over Complex Terrain

The terrain between grid points is used to modify locally the background error correlation matrix in an objective analysis system. This modification helps to reduce the influence across mountain barriers of corrections to the background field that are derived from surface observations. This change to the background error correlation matrix is tested using an analytic case of surface temperature that encapsulates the significant features of nocturnal radiation inversions in mountain basins, which can be difficult to analyze because of locally sharp gradients in temperature. Bratseth successive corrections, optimal interpolation, and three-dimensional variational approaches are shown to yield exactly the same surface temperature analysis. Adding the intervening terrain term to the Bratseth approach led to solutions that match more closely the specified analytic solution. In addition, the convergence of the Bratseth solutions to the best linear unbiased estimation of the analytic solution is faster. The intervening terrain term was evaluated in objective analyses over the western United States derived from a modified version of the Advanced Regional Prediction System Data Assimilation System. Local adjustment of the background error correlation matrix led to improved surface temperature analyses by limiting the influence of observations in mountain valleys that may differ from the weather conditions present in adjacent valleys.