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The NASA/JPL airborne precipitation radar APR-2 (cross-track scanning, dual-frequency - 14 and 35 GHz, Doppler and dual polarization, see Sadowy et al. (2003) for detailed description of the instrument) was operated on the NASA P-3 aircraft during the Wakasa Bay experiment.
The simultaneous use of the Taiwan VHF radar and the HF Doppler sounder for remote measurement of three-dimensional winds, gravity waves, and density perturbations at mesospheric and thermospheric heights is demonstrated. A special event of atmospheric disturbances caused by propagating gravity waves excited by weak convective motions in winter time were investigated. The three-dimensional wind velocities at different heights were determined, and the frequency, horizontal wavelength, vertical wavelength, and phase velocity of the gravity waves were measured. The subtropical, low-latitude site makes the VHF radar and HF Doppler array systems unique, and the observations especially valuable for space projects dealing with low-latitude atmosphere.
The UHF-band and S-band research radars of NASA Goddard's atmospheric sciences research facility at Wallop's Island, Virginia are used to study the correlation between the location of radar-detected electrical activity in a storm cell and its precipitation reflectivity structure. The technique used to make the measurements is discussed and some typical results are presented. The existence of a bimodal distribution of lightning activity as a function of altitude is reported and supported by the data. The vertical structure of the electrical activity may be evidence of K and/or J processes. The technique used is very valuable, and provides high-resolution radar data of both reflectivities and flash density.
ERS-1 and ERS-2 scatterometer and synthetic aperture radar (SAR) data are used to monitor and track large and small scale sea ice dynamics in the Southern Ocean, and in particular in the Weddell Sea, Antarctica. Sea ice formation in the Weddell Sea regulates vertical and horizontal thermohaline circulation and influences bottom water production rates. Significant seasonal to interannual variability is observed in the sea ice drift dynamics. Coupled model simulations reproduce this variability and indicate that there is significant interannual variability in Weddelll Sea ice formation, drifts and extent on the El Nino southern oscillation (ENSO) timescale, with a period of approximately eight years. Changes in ice dynamics on these timescales regulate the amount of sea ice divergence and polynya formation. Anomalies in the timing and duration of the opening of the Ronne ice shelf polynya system are closely related to the variability in outflow of Weddell Sea bottom water measured at Joinville Island.
The technique of F region sounding by HF coherent radar is applied to the study of field line resonances equatorward of a region of shear flow in the early morning sector. The motions were predominantly in the geomagnetic east-west direction, indicating north-south electric fields. These oscillations had pronounced peaks in their latitudinal power distribution. For the pulsation at 1.95 mHz, a latitudinal phase shift of 180 deg was observed across the peaks in all the look directions of the radar, and a longitudinal wavelength corresponding to an m value of 3 was obtained. For the 2.6-mHz pulsation, the phase shifts across the peaks had a variation with a look direction that indicated a significant longitudinal as well as latitudinal variation; for this activity, an m value of about 16 is estimated. These features are interpreted in terms of the field line resonance theory, and the possible sources of the pulsation energy are discussed.
Air dehydrates to stratospheric abundances in the tropical tropopause layer (TTL). The role of overshooting convection in the dehydration process is not well understood. To study this effect, we use the TRMM (Tropical Rainfall Measuring Mission) precipitation radar (PR) to measure the altitudes of cloud tops forming in the TTL. Because the radar signal is dominated by scatter from large particles, these cloud observations imply the presence of strong convective systems with large updraft. Both winter and summer data from two different years are examined to study both interseasonal and interannual variability. The global distribution of these clouds is in good agreement with those of the surface precipitation rates. In addition, the altitude distributions of these clouds follow an exponential dependence. However, clouds over continental regions typically extend to higher altitudes in the tropics. Almost no cloud tops were observed above 20 km. Comparison between the radar cloud tops and colocated IR brightness temperature measurements reveal a large difference in both the diurnal cycle and intensity between continental and oceanic convection.
Remote sensing by ground-based HF radar and airborne synthetic aperture radar and in situ wave measurements performed on March 25, 1977 during the West Coast Experiment have made it possible to form an overall picture of the 7-sec-period wave climate over a 35,000 sq km region off the southern California coast. The picture which emerges from these measurements shows a broad deep-ocean directional distribution arriving from the west and being significantly modified as it travels coastward passing San Clemente and Santa Catalina islands.
In a controlled experiment a ground photometer and radar station recorded an increase in night sky luminescence following injection of an electron beam into the atmosphere from a rocket at altitudes 80 to 154 km. A main and supplementary scattering and luminescene regions were observed. The effect is presumed to be due to electron eruption induced by artificial action on the magnetosphere.
Ocean wave spectra from bistatic radar scatter data, using time delay Doppler-frequency map
This paper describes the original Debris Environment Characterization Radar concept and the design verification experiments developed and carried out with the purpose of establishing methods for assessing the hazards to the Space Station Freedom from radar measurements. Three design verification experiments, utilizing the Arecibo, the Goldstone, and the ALCOR radars were performed. Data obtained from RCS measurements of a representative sample of debris from ground-test hypervelocity impacts and from explosions of simulated satellites will be used to establish a relationship between the physical size of a randomly shaped debris object and its RCS.
Delay-Doppler observations at 12.6 cm which have been used to estimate the relative radar reflectivities of Saturn's classical ring sections show that the A and B rings are responsible for most of the radar echo, and that the average radar reflectivity per unit of projected area of the A ring is 90% as large as the B ring. No firm evidence is found for radar backscattering from particles interior to the B ring, exterior to the A ring, of from the planet itself. Unexpectedly large amounts of power at Doppler shifts near the center of the echo spectrum, which had been reported at 3.5 and 12.6 cm for ring plane tilt angles greater than 24.4 deg are not apparent in spectra for those wavelengths obtained at ring plane tilt angles smaller than 21.4 deg.
Simultaneous observations of both the precipitation and the lightning associated with thunderstorms show that the lightning is within 3 km of the maximum precipitation echo. The intensity and type of the precipitation is observed with 500 m spatial accuracy using an S-band polarization radar and the position of the lightning is inferred from a low frequency magnetic direction finding location system. Empirical adjustment to the angles using the redundancy of the lightning data reduce this error. Radar echoes above 45dBZ may be caused by soft hail or hailstones, but similarly intense echoes may result from melting snow. The data show that a new polarization radar parameter, the linear depolarization ratio, can distinguish between soft hail and melting snow, and that the intense radar echoes associated with melting snow pose no threat of lightning. A lightning risk only exists when the radar indicates that the clouds contain soft hail or hailstones.
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The measurement of ocean surface waves with a nanosecond radar pulse from a fixed platform at vertical incidence is discussed. By reducing the pulse width of radar until the pulse width resolves the vertical water wave structure, a set of radar returns is available to describe the ocean surface characteristics which differs from returns obtained by conventional radars. A block diagram of the radar and the principles of operation are presented.
E- and lower F-region data obtained by the incoherent scatter radar of Chatanika, Alaska were used to analyze the height-integrated Hall and Pedersen conductivities, electric fields, ionospheric currents, electron densities, and rate of heating of the neutral atmosphere by particle precipitation and by electric current dissipation during the period of intense solar flares, August 4-7, 1972. Although the magnetosphere was unusually disturbed magnetically, the radar data were in general not particularly larger than those seen during more quiet periods. Chatanika seemed to be in the auroral oval during nearly the whole of the time period studied, implying a greatly expanded size of the oval.
A statistical modeling of rain cell characteristics is presented; the modeling is based on high-resolution radar measurements of the cell structure. The analysis of the fine-scale three-dimensional structure of summer rainshowers in the mid-Atlantic region leads to statistical descriptions of the rain cells in terms of a variety of physical cell parameters. Core reflectivity profiles, contour area, and altitude extent of the cells have been determined along with the frequency of occurrence for various storm classes and categories. The statistical descriptions of the rain cells for the mid-Atlantic region were compared to descriptions for other areas, and the similarities and differences are described. Simplified models of rain cells based on the statistical descriptions are developed for the different rain categories as a function of frequency of occurrence.
Since 1991, the European Space Agency's two ERS satellites have aquired microwave radar data of Antarctica. ERS data have been recorded by two receiving stations, one German, one Japanese.