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Robert F. Contreras

Abstract

Reynolds sea surface temperature (SST) data showing tropical instability waves (TIWs) in the tropical Pacific are analyzed along with current measurements from the Tropical Atmosphere–Ocean (TAO) buoy array and wind speeds from the European Remote Sensing Satellite (ERS) -1 and -2 scatterometers. TIWs are visible as undulations in the SST cold fronts that delineate the northern and southern boundaries of the cold tongue in the equatorial Pacific. The SST pattern results from advection of the SST front by instabilities in the near-surface equatorial currents. Although the waves are seen on both sides of the Pacific cold tongue and north of the equator in the Atlantic, they are most intense, and thereby most observable, in the north equatorial Pacific. The combination of data used in this analysis provides information about these waves, the factors controlling them, and their coupling to the atmosphere on annual and interannual timescales. On annual timescales, the TIWs generally establish a strong signal in July east of about 140°W with a westward phase speed of about 0.5 m s−1. By August, the waves usually occupy the longitudes between 160° and 100°W and continue to propagate west at roughly the same speed. With the onset of the warm season in the equatorial cold tongue (spring), the signal typically weakens and the propagation speeds show large variations. On interannual timescales, activity is strongest during the cold phase of the ENSO cycle (La Niña) when the cold tongue is most pronounced; the waves are weak or nonexistent during the warm phase of ENSO (El Niño) when the SST front is weak. The TIW signature in SST is noticeable throughout all seasons of the year provided that the gradient in SST at 140°W is greater than about 0.25°C (100 km)−1. In addition, analysis of the currents underlines the importance of the background currents to the zonal propagation speeds.

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Robert F. Contreras and Stephen J. Frasier

Abstract

High spatial and temporal resolution S-band radar observations of insects in the atmospheric boundary layer (ABL) are described. The observations were acquired with a frequency-modulated continuous-wave (FMCW) radar during the 2002 International H20 Project (IHOP_2002) held in Oklahoma in the months of May and June 2002. During the observational period the boundary layer was convective with a few periods of rain. Rayleigh scattering from particulate scatterers (i.e., insects) dominates the return; however, Bragg scattering from refractive index turbulence is also significant, especially at the top of the afternoon boundary layer. There is a strong diurnal signal in the insect backscatter: minima in the morning and at dusk and maxima at night and midafternoon. Insect number densities and radar cross sections (RCSs) are calculated. The RCS values range from less than 10−12 m2 to greater than 10−7 m2 and likewise have a strong diurnal signal. These are converted to equivalent reflectivity measurements that would be reported by typical meteorological radars. The majority of reflectivity measurements from particulate scatterers ranges from −30 to −5 dBZ; however, intense point scatterers (>10 dBZ) are occasionally present. The results show that although insects provide useful targets for characterization of the clear-air ABL, the requirements for continuous monitoring of the boundary layer are specific to time of day and range from −20 dBZ in the morning to −10 to −5 dBZ in the afternoon and nocturnal boundary layer (NBL).

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David McLaughlin, David Pepyne, V. Chandrasekar, Brenda Philips, James Kurose, Michael Zink, Kelvin Droegemeier, Sandra Cruz-Pol, Francesc Junyent, Jerald Brotzge, David Westbrook, Nitin Bharadwaj, Yanting Wang, Eric Lyons, Kurt Hondl, Yuxiang Liu, Eric Knapp, Ming Xue, Anthony Hopf, Kevin Kloesel, Alfred DeFonzo, Pavlos Kollias, Keith Brewster, Robert Contreras, Brenda Dolan, Theodore Djaferis, Edin Insanic, Stephen Frasier, and Frederick Carr

Dense networks of short-range radars capable of mapping storms and detecting atmospheric hazards are described. Composed of small X-band (9.4 GHz) radars spaced tens of kilometers apart, these networks defeat the Earth curvature blockage that limits today s long-range weather radars and enables observing capabilities fundamentally beyond the operational state-of-the-art radars. These capabilities include multiple Doppler observations for mapping horizontal wind vectors, subkilometer spatial resolution, and rapid-update (tens of seconds) observations extending from the boundary layer up to the tops of storms. The small physical size and low-power design of these radars permits the consideration of commercial electronic manufacturing approaches and radar installation on rooftops, communications towers, and other infrastructure elements, leading to cost-effective network deployments. The networks can be architected in such a way that the sampling strategy dynamically responds to changing weather to simultaneously accommodate the data needs of multiple types of end users. Such networks have the potential to supplement, or replace, the physically large long-range civil infrastructure radars in use today.

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