Browsing by Author "Balsley, B. B."
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Item Open Access Differences in near-mesopause summer winds, temperatures, and water vapor at nothern and southern latitudes as possible causal factors for inter-hemispheric PMSE differences(American Geophysical Union, 1999-06-01) Huaman, M. M.; Balsley, B. B.We report the results of a recent study to examine possible causal factors that could explain the observed differences in PMSE intensity in the northern and southern hemispheres. A variety of satellite data, models and ground‐based radar observations in the two hemispheres during local summer have been examined in this attempt. We will show results of inter‐hemispheric comparisons of temperatures, winds, and water vapor. The primary conclusions that can be drawn from these studies are that, while water vapor differences in the two hemispheres are difficult to interpret at near‐mesopause altitudes, the inter‐hemispheric temperature comparisons show clearly that the southern hemispheric mesopause is indeed a few degrees warmer. Moreover, southern summer mesospheric mean winds are considerably weaker than they are in the north. These results provide support for earlier speculations that were made to explain the observed inter‐hemispheric difference in PMSE occurrence.Item Open Access First observations of polar mesosphere summer echoes in Antarctica(American Geophysical Union, 1999-10-01) Woodman Pollitt, Ronald Francisco; Balsley, B. B.; Aquino, F.; Flores, L.; Vásquez, E.; Sarango, M.; Huamán, M. M.; Soldi, H.A 25‐kW peak power 50‐MHz radar was installed at the Peruvian base on King George Island, Antarctica (62°S), in early 1993. A search for polar mesospheric summer echoes (PMSEs) was made during late January and early February of the first year of operation with negative results. These results have been reported in the literature [Balsley et al., 1993; 1995]. We report here results obtained during the austral summer of the second year (1994) of operation. Observations during the second year were begun earlier, i.e., closer to the austral summer solstice. PMSEs were observed during this period, albeit the echoes were much weaker than what one would expect based on earlier Poker Flat radar results at a comparable latitude (65°N) in the Northern Hemisphere. A large and measurable asymmetry in PMSE strength in the two hemispheres therefore exists. We explain this asymmetry by postulating a difference in summer mesopause temperatures between the two hemispheres of ∼7.5 K. This difference has been estimated using an empirical relationship between the variations of the Poker Flat PMSE power as a function of temperature given by the mass spectrometer incoherent scatter extended (MSISE‐90) model.Item Restricted Oblique VHF radar spectral studies of the equatorial electrojet(American Geophysical Union, 1975-04-01) Fejer, B. G.; Farley, D. T.; Balsley, B. B.; Woodman Pollitt, Ronald FranciscoA new narrow‐beam antenna at the Jicamarca Observatory permits oblique (zenith angle, 25°) radar spectral studies of the electrojet with an altitude resolution down to 1.1 km. Only daytime observations are possible presently, however. The general altitude variations in spectral shape observed are consistent with linear instability theory, if the effect of recombination is included. The height at which the mean Doppler shift of the echo maximizes, however, is about 4 km higher than one would expect on the basis of electrojet models. An increase in the assumed collision frequency would remove the discrepancy. Other data presented strongly suggest that at least some of the variations observed in the type 1 echo phase velocity are due to changes in the temperature of the E region.Item Restricted Radar observations of two‐dimensional turbulence in the equatorial electrojet, 2(American Geophysical Union, 1976-01-01) Fejer, B. G.; Farley, D. T.; Balsley, B. B.; Woodman Pollitt, Ronald FranciscoObservations with an altitude resolution of about 1 km were made with the large, vertically directed 50‐MHz radar system at the Jicamarca Radar Observatory during the day, when the electrojet was strong. Type 1 (‘two stream’) echoes were seen in a limited range of altitudes, with Doppler shifts corresponding to upward and downward motion at the acoustic velocity. Most of the radar returns were due to type 2 echoes, however. The direction of motion of the type 1 waves sometimes reversed in as little as 1 s, supporting a turbulent model of the electrojet region. During the day the upgoing type 1 waves were observed to be somewhat more easily excited than the downgoing waves, an effect similar to an east‐west asymmetry noted in earlier studies. The correspondence between the Jicamarca radar observations and rocket measurements in India is discussed.Item Restricted Radar studies of anomalous velocity reversals in the equatorial ionosphere(American Geophysical Union, 1976-09-01) Fejer, B. G.; Farley, D. T.; Balsley, B. B.; Woodman Pollitt, Ronald FranciscoRadar observations made at Jicamarca show that the equatorial electrojet current and the E and F region electric fields can reverse from their normal direction during the day or night and during magnetically quiet or disturbed conditions. The nighttime reversals can only be detected by such radar measurements. The observations support most of the current hypotheses concerning the electrojet plasma instabilities. The rapid reversals sometimes seen during disturbed conditions indicate that high‐latitude currents and electric fields associated with substorm activity strongly perturb the dynamo current system at all latitudes.Item Restricted Report from the International Workshop on Remote Sensing in Geophysics Using Doppler Techniques(American Meteorological Society, 1998) Brandolini, A.; Balsley, B. B.; Mabres, A.; Woodman Pollitt, Ronald Francisco; Capsoni, C.; D'Amico, M.; Ecklund, W. L.; Hagfors, T.; Harper, R.; Heron, M. L.; Hocking, W. K.; Lehtinen, M. S.; Rottger, J.; Sarango, M. F.; Sato, T.; Stauch, R. J.; Vaughn, J. M.; Wyatt, L. R.; Zrnic, D. S.Presents a summary of a meeting staged by the International Workshop on Remote Sensing in Geophysics Using Doppler Techniques, which was held on March 5, 1996 in Bellagio, Italy at the Rockefeller Study and Conference Center.Item Restricted Southern-hemisphere PMSE: Where are they?(American Geophysical Union, 1993-09) Balsley, B. B.; Woodman Pollitt, Ronald Francisco; Sarango, M.; Urbina, J.; Rodríguez, R.; Ragaini, E.; Carey, J.We report a surprising absence of PMSE (Polar Mesospheric Summer Echoes) in VHF radar observations of the southern summer high-latitude mesosphere. Our observations cover about twenty days during January-February, 1993, from King George Island, Antarctica.Item Restricted Vertical structure of the VHF backscattering region in the equatorial electrojet and the gradient drift instability(American Geophysical Union, 1975-04-01) Fejer, B. G.; Farley, D. T.; Balsley, B. B.; Woodman Pollitt, Ronald FranciscoRadar measurements made with high spatial resolution and large dynamic range at the Jicamarca Radar Observatory near the time of reversal of the electrojet current provide further proof that the gradient drift instability is in fact responsible for the type 2 irregularities. Echoes are received over a much wider range of altitudes at night than during the day partly because of the change in character of the background electron density profile and partly because of recombination effects, which can be important during the day. It is also shown that one must be cautious, particularly at night, in associating the mean Doppler shift of oblique radar echoes with the maximum east‐west electron drift velocity.