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Kermit K. Keeter
,
Steven Businger
,
Laurence G. Lee
, and
Jeff S. Waldstreicher

Abstract

Winter weather in the Carolinas and Virginia is highly variable and influenced by the area's diverse topography and geography. The Gulf Stream, the highest mountains in the Appalachians, the largest coastal lagoonal system in the United States, and the region's southern latitude combine to produce an array of weather events, particularly during the winter season, that pose substantial challenges to forecasters. The influence of the region's topography upon the evolution of winter weather systems, such as cold-air damming and frontogenesis, is discussed. Conceptual models and specific case studies are examined to illustrate the region's vast assortment of winter weather hazards including prolonged heavy sleet, heavy snow, strong convection, and coastal flooding.

The weather associated with these topographic and meteorological features is often difficult for operational dynamical models to resolve. Forecasting precipitation type within the region can be especially difficult. An objective technique to forecast wintry precipitation across North Carolina is presented to illustrate a 1ocally developed forecast tool used operationally to supplement the centrally produced numerical guidance. The development of other forecast tools is being pursued through collaborative studies between the National Weather Service Forecast Office in Raleigh–Durham, North Carolina, and the Department of Marine, Earth and Atmospheric Sciences at North Carolina State University.

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Michael Bevis
,
Steven Businger
,
Steven Chiswell
,
Thomas A. Herring
,
Richard A. Anthes
,
Christian Rocken
, and
Randolph H. Ware

Abstract

Emerging networks of Global Positioning System (GPS) receivers can be used in the remote sensing of atmospheric water vapor. The time-varying zenith wet delay observed at each GPS receiver in a network can be transformed into an estimate of the precipitable water overlying that receiver. This transformation is achieved by multiplying the zenith wet delay by a factor whose magnitude is a function of certain constants related to the refractivity of moist air and of the weighted mean temperature of the atmosphere. The mean temperature varies in space and time and must be estimated a priori in order to transform an observed zenith wet delay into an estimate of precipitable water. We show that the relative error introduced during this transformation closely approximates the relative error in the predicted mean temperature. Numerical weather models can be used to predict the mean temperature with an rms relative error of less than 1%.

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Steven Businger
,
Steven R. Chiswell
,
Michael Bevis
,
Jingping Duan
,
Richard A. Anthes
,
Christian Rocken
,
Randolph H. Ware
,
Michael Exner
,
T. VanHove
, and
Fredrick S. Solheim

This paper provides an overview of applications of the Global Positioning System (GPS) for active measurement of the Earth's atmosphere. Microwave radio signals transmitted by GPS satellites are delayed (refracted) by the atmosphere as they propagate to Earth-based GPS receivers or GPS receivers carried on low Earth orbit satellites.

The delay in GPS signals reaching Earth-based receivers due to the presence of water vapor is nearly proportional to the quantity of water vapor integrated along the signal path. Measurement of atmospheric water vapor by Earth-based GPS receivers was demonstrated during the GPS/STORM field project to be comparable and in some respects superior to measurements by ground-based water vapor radiometers. Increased spatial and temporal resolution of the water vapor distribution provided by the GPS/STORM network proved useful in monitoring the moisture-flux convergence along a dryline and the decrease in integrated water vapor associated with the passage of a midtropospheric cold front, both of which triggered severe weather over the area during the course of the experiment.

Given the rapid growth in regional networks of continuously operating Earth-based GPS receivers currently being implemented, an opportunity exists to observe the distribution of water vapor with increased spatial and temporal coverage, which could prove valuable in a range of operational and research applications in the atmospheric sciences.

The first space-based GPS receiver designed for sensing the Earth's atmosphere was launched in April 1995. Phase measurements of GPS signals as they are occluded by the atmosphere provide refractivity profiles (see the companion article by Ware et al. on page 19 of this issue). Water vapor limits the accuracy of temperature recovery below the tropopause because of uncertainty in the water vapor distribution. The sensitivity of atmospheric refractivity to water vapor pressure, however, means that refractivity profiles can in principle yield information on the atmospheric humidity distribution given independent information on the temperature and pressure distribution from NWP models or independent observational data.

A discussion is provided of some of the research opportunities that exist to capitalize on the complementary nature of the methods of active atmospheric monitoring by GPS and other observation systems for use in weather and climate studies and in numerical weather prediction models.

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Jingping Duan
,
Michael Bevis
,
Peng Fang
,
Yehuda Bock
,
Steven Chiswell
,
Steven Businger
,
Christian Rocken
,
Frederick Solheim
,
Terasa van Hove
,
Randolph Ware
,
Simon McClusky
,
Thomas A. Herring
, and
Robert W. King

Abstract

A simple approach to estimating vertically integrated atmospheric water vapor, or precipitable water, from Global Positioning System (GPS) radio signals collected by a regional network of ground-based geodetic GPS receiver is illustrated and validated. Standard space geodetic methods are used to estimate the zenith delay caused by the neutral atmosphere, and surface pressure measurements are used to compute the hydrostatic (or “dry”) component of this delay. The zenith hydrostatic delay is subtracted from the zenith neutral delay to determine the zenith wet delay, which is then transformed into an estimate of precipitable water. By incorporating a few remote global tracking stations (and thus long baselines) into the geodetic analysis of a regional GPS network, it is possible to resolve the absolute (not merely the relative) value of the zenith neutral delay at each station in the augmented network. This approach eliminates any need for external comparisons with water vapor radiometer observations and delivers a pure GPS solution for precipitable water. Since the neutral delay is decomposed into its hydrostatic and wet components after the geodetic inversion, the geodetic analysis is not complicated by the fact that some GPS stations are equipped with barometers and some are not. This approach is taken to reduce observations collected in the field experiment GPS/STORM and recover precipitable water with an rms error of 1.0–1.5 mm.

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Steven P. Oncley
,
Carl A. Friehe
,
John C. Larue
,
Joost A. Businger
,
Eric C. Itsweire
, and
Sam S. Chang

Abstract

An atmospheric surface-layer experiment over a nearly uniform plowed field was performed to determine the constants in the flux-profile similarity formulas, particularly the von Kármán constant. New instruments were constructed to minimize flow distortion effects on the turbulence measurements and to provide high-resolution gradient measurements. In addition, a hot-wire anemometer directly measured the turbulent kinetic energy dissipation rate.

An average value of the von Kármán constant of 0.365 ± 0.015 was obtained from 91 runs (31 h) in near-neutral stability conditions. However, four near-neutral runs when snow covered the ground gave an average value of 0.42. This result suggests that the von Kármán constant depends on the roughness Reynolds number, which may resolve some of the differences in previous determinations over different surfaces. The one-dimensional Kolmogorov inertial subrange constant was found to have a value of 0.54 ± 0.03, slightly larger than previous results.

The flux-profile relations for momentum and temperature variance were evaluated, and humidity variance data behaved similarly to temperature. Dissipation of turbulent kinetic energy was found to be less than production under near-neutral conditions, which suggests that turbulent or pressure transport may be significant.

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Paolo Antonelli
,
Henry E. Revercomb
,
Graziano Giuliani
,
Tiziana Cherubini
,
Steven Businger
,
Ryan Lyman
,
Stephen Tjemkes
,
Rolf Stuhlmann
, and
Jean-Luc Moncet

Abstract

The Space Science Engineering Center, in collaboration with the Mauna Kea Weather Center at the University of Hawai’i at Mānoa, has developed a regional retrieval processor for high-spectral-resolution infrared data. The core of the processor makes use of an inversion system, referred to as Mirto, which combines, in a Bayesian way, the a priori knowledge of the atmospheric state, based on available numerical weather prediction forecasts, with the physical information embedded in satellite observations. Forecast temperature and water vapor mixing ratio fields over the central North Pacific Ocean are adjusted to produce synthetic radiances closer and closer to the Suomi NPP Cross-track Infrared Sounder (CrIS) observations taken in clear-sky conditions. The paucity of synoptic observations over this area and the highly homogeneous background represented by the ocean provide a good framework for the implementation of this hyperspectral data inversion system. Nearly real-time (less than 60 min from overpass time) Internet publication of retrieved atmospheric profiles is made possible by the availability of a direct broadcast system that provides data from the Suomi NPP platform (CrIS and VIIRS). The main goal for the implemented system is to provide the forecasting community with products suitable for nowcasting applications and for optimal data assimilation. The implemented processor has been running routinely since August 2013. Validation based on the comparisons of retrievals with rawinsonde data from Hilo, Hawaii, and Lihue, Hawaii, and GPS-derived total precipitable water from four stations, performed over a time period of more than 1 year, shows a statistically significant improvement on the background atmospheric state used as a priori information.

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Antti T. Pessi
,
Steven Businger
,
K. L. Cummins
,
N. W. S. Demetriades
,
M. Murphy
, and
B. Pifer

Abstract

The waveguide between the earth’s surface and the ionosphere allows very low-frequency (VLF) emissions generated by lightning, called sferics, to propagate over long distances. The new Pacific Lightning Detection Network (PacNet), as a part of a larger long-range lightning detection network (LLDN), utilizes this attribute to monitor lightning activity over the central North Pacific Ocean with a network of ground-based lightning detectors that have been installed on four widely spaced Pacific islands (400–3800 km). PacNet and LLDN sensors combine both magnetic direction finding (MDF) and time-of-arrival (TOA)-based technology to locate a strike with as few as two sensors. As a result, PacNet/LLDN is one of the few observing systems, outside of geostationary satellites, that provides continuous real-time data concerning convective storms throughout a synoptic-scale area over the open ocean.

The performance of the PacNet/LLDN was carefully assessed. Long-range lightning flash detection efficiency (DE) and location accuracy (LA) models were developed with reference to accurate data from the U.S. National Lightning Detection Network (NLDN). Model calibration procedures are detailed, and comparisons of model results with lightning observations from the PacNet/LLDN in correlation with NASA’s Lightning Imaging Sensor (LIS) are presented. The daytime and nighttime flash DE in the north-central Pacific is in the range of 17%–23% and 40%–61%, respectively. The median LA is in the range of 13–40 km. The results of this extensive analysis suggest that the DE and LA models are reasonably able to reproduce the observed performance of PacNet/LLDN.

The implications of this work are that the DE and LA model outputs can be used in quantitative applications of the PacNet/LLDN over the North Pacific Ocean and elsewhere. For example, by virtue of the relationship between lightning and rainfall rates, these data also hold promise as input for NWP models as a proxy for latent heat release in convection. Moreover, the PacNet/LLDN datastream is useful for investigations of storm morphology and cloud microphysics over the central North Pacific Ocean. Notably, the PacNet/LLDN lightning datastream has application for planning transpacific flights and nowcasting of squall lines and tropical storms.

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James J. Gurka
,
Eugene P. Auciello
,
Anthony F. Gigi
,
Jeff S. Waldstreicher
,
Kermit K. Keeter
,
Steven Businger
, and
Laurence G. Lee

Abstract

The complex combination of synoptic and mesoscale interactions, topographic influences, and large population densities poses a multitude of challenging problems to winter weather forecasters throughout the eastern United States. Over the years, much has been learned about the structure, evolution, and attendant precipitation within winter storms. As a result, numerous operational procedures, forecast applications, and objective techniques have been developed at National Weather Service offices to assess the potential for, and forecast, hazardous winter weather. A companion paper by Maglaras et al. provided an overview of the challenge of forecasting winter weather in the eastern United States.

This paper focuses on the problem of cyclogenesis from an operational perspective. Since pattern recognition is an important tool employed by field forecasters, a review of several conceptual models of cyclogenesis often observed in the east is presented. These include classical Miller type A and B cyclogenesis, zipper lows, 500-mb cutoff lows, and cold-air cyclogenesis. The ability of operational dynamical models to predict East Coast cyclones and, in particular, explosive cyclogenesis is explored. An operational checklist that utilizes information from the Nested Grid Model to forecast the potential for rapid cyclogenesis is also described. A review of signatures related to cyclogenesis in visible, infrared, and water vapor satellite imagery is presented. Finally, a study of water vapor imagery for 16 cases of explosive cyclogenesis between 1988 and 1990 indicates that an acceleration of a dry (dark) surge with speeds exceeding 25 m s−1, toward a baroclinic zone, is an excellent indicator of the imminent onset of rapid deepening.

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Laurence G. Lee
,
Rodney F. Gonski
,
Eugene P. Auciello
,
James R. Poirier
,
Robert A. Marine
,
Steven Businger
,
Kenneth D. Lapenta
,
Robert W. Kelly
, and
Thomas A. NizioL

Abstract

No abstract available

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