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S. L. Stanford, M. A. Lind, and G. S. Takle

Abstract

Electromagnetic noise from six convective storms in Iowa has been studied at a variety of frequencies from 0.67 to 144 MHz, with the majority of the data being recorded at 53 MHz. The quasi-static atmospheric electric field was also studied. Twelve tornadoes, numerous funnel clouds and several hailstorms occurred during these storms. Eleven of the tornadoes appear to correlate with some type of enhancement of the recorded electromagnetic pulse rate. A spectacular peak in pulse rate during Storm No. 5 is attributed to a brief but destructive tornado at 38 km; the event is discussed in detail. One tornado at long range, the longest lived of the season, showed no correlation and is thought to represent a minority class of tornadoes which exhibit little electromagnetic noise generation. Good time correlation is also achieved between data events and several hailstorms and funnel clouds. Except for the closest events (<20 km), the region above 1 MHZ appears to be a better indicator of tornadic activity than that portion of the radio spectrum below 1 MHz. The data also reveal a number of pulse-rate peaks which could not be correlated with known severe weather events.

Four and possibly five types of radio noise observed from severe storms are described, along with some initial suggestions about the possible mechanisms involved. The lack of understanding of the basic physics involved is indicated and the need for more observational data is emphasized.

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M. A. Lind, J. S. Hartman, E. S. Takle, and J. L. Stanford

Abstract

The purpose of this note is to show that not all tornadic storms yield the same radio-frequency noise behavior. One funnel cloud observed gave significant radio noise over a frequency range from 2.5 to 144 MHz.

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H. L. Johnson Jr., R. D. Hart, M. A. Lind, R. E. Powell, and J. L. Stanford

Abstract

Thunderstorm radio noise measurements at several frequencies in the range 0.01–74 MHz have been made with specially designed remote recording stations in Iowa. The data were recorded during the spring and summer of 1974 when a series of severe storm systems produced a great number of large hail and tornado reports in Iowa. Computer analyses were made of nearly a billion bits of data, corresponding to 170 h of real-time recordings. Careful compilations of surface severe weather reports, hail damage information from insurance companies, and studies on the Des Moines WSR-57 radar echoes were compared with the analyzed radio noise data. The results include the following:

1) In agreement with earlier work, large‐amplitude radio noise impulse rates were found to he generally good indicators of thunderstorm severity. Although the majority of the radio energy radiated from major lightning strokes occurs in the 0.01 MHz range, this frequency was found to be a poor indicator of storm severity; the higher frequencies (megahertz range) were considerably better. The character of the noise appears similar at 2.5 and 74 MHz.

2) In at least five cases, tornadic events correlated in time with radio noise count rate peaks. One funnel cloud was reported equidistant at 60 km from two recording stations and coincident with count rate peaks at both stations, lending credence to the idea that the peak was associated with the storm occurrence, rather than with corona or other local effects.

3) No unusual radio noise was recorded during the lifetime of a small, verified tornado at 19 km range. In addition, the count rates for its parent thunderstorm would not have indicated severity.

In spite of inherent atmospheric variableness, the radio noise technique is a useful complementary indicator of storm severity.

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Qing Wang, Denny P. Alappattu, Stephanie Billingsley, Byron Blomquist, Robert J. Burkholder, Adam J. Christman, Edward D. Creegan, Tony de Paolo, Daniel P. Eleuterio, Harindra Joseph S. Fernando, Kyle B. Franklin, Andrey A. Grachev, Tracy Haack, Thomas R. Hanley, Christopher M. Hocut, Teddy R. Holt, Kate Horgan, Haflidi H. Jonsson, Robert A. Hale, John A. Kalogiros, Djamal Khelif, Laura S. Leo, Richard J. Lind, Iossif Lozovatsky, Jesus Planella-Morato, Swagato Mukherjee, Wendell A. Nuss, Jonathan Pozderac, L. Ted Rogers, Ivan Savelyev, Dana K. Savidge, R. Kipp Shearman, Lian Shen, Eric Terrill, A. Marcela Ulate, Qi Wang, R. Travis Wendt, Russell Wiss, Roy K. Woods, Luyao Xu, Ryan T. Yamaguchi, and Caglar Yardim

Abstract

The Coupled Air–Sea Processes and Electromagnetic Ducting Research (CASPER) project aims to better quantify atmospheric effects on the propagation of radar and communication signals in the marine environment. Such effects are associated with vertical gradients of temperature and water vapor in the marine atmospheric surface layer (MASL) and in the capping inversion of the marine atmospheric boundary layer (MABL), as well as the horizontal variations of these vertical gradients. CASPER field measurements emphasized simultaneous characterization of electromagnetic (EM) wave propagation, the propagation environment, and the physical processes that gave rise to the measured refractivity conditions. CASPER modeling efforts utilized state-of-the-art large-eddy simulations (LESs) with a dynamically coupled MASL and phase-resolved ocean surface waves. CASPER-East was the first of two planned field campaigns, conducted in October and November 2015 offshore of Duck, North Carolina. This article highlights the scientific motivations and objectives of CASPER and provides an overview of the CASPER-East field campaign. The CASPER-East sampling strategy enabled us to obtain EM wave propagation loss as well as concurrent environmental refractive conditions along the propagation path. This article highlights the initial results from this sampling strategy showing the range-dependent propagation loss, the atmospheric and upper-oceanic variability along the propagation range, and the MASL thermodynamic profiles measured during CASPER-East.

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