Browsing by Author "Larsen, M. F."
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Item Open Access An analysis technique for deriving vector winds and in-beam incidence angles from radar interferometer measurements(American Meteorological Society, 1992-02) Larsen, M. F.; Palmer, R. D.; Fukao, S.; Woodman Pollitt, Ronald Francisco; Yamamoto, M; Tsuda, T; Kato, S.We present a method for deriving horizontal velocities, vertical velocities, and in-beam incidence angles from radar interferometer data. All parameters are calculated from the slope and intercept of straight lines fitted in a least-squares sense to the variation of the signal phase as a function of radial velocity for each pair of receiving antennas. Advantages of the method are that the calculations are computationally fast and simple, and the analysis leads to relatively simple expressions for the uncertainty in the velocity measurements.Item Restricted Fine structure in midlatitude sporadic E layers(Elsevier, 2013-01-03) Hysell, D. L.; Nossa, E.; Aveiro, H. C.; Larsen, M. F.; Munro, J.; Sulzer, M. P.; González, S. A.Fine structure in midlatitude sporadic E layer patches or “clouds” is apparent in incoherent scatter observations from the Arecibo Radio Telescope. The fine structure is wavelike with predominant horizontal wavelengths as large as about 2–3 km. We attribute the structure to a drift wave instability operating in the collisional regime. A linear, local dispersion relation for the waves is described which predicts growth driven by polarization electric fields in the cloud. A numerical simulation produces wave growth and other features consistent with the dispersion relation, including finite parallel wavenumbers. The kilometric irregularities are thought to be the primary waves from which secondary, meter-scale waves in the layers can form.Item Restricted Gravity-wave generation by thunderstorms observed with a vertically-pointing 430 MHz radar(American Geophysical Union, 1982-05) Larsen, M. F.; Swartz, W.E.; Woodman Pollitt, Ronald FranciscoDuring September of 1979, the Arecibo Observatory 430 MHz Doppler radar was used to study the upper troposphere and lower stratosphere during thunderstorm activity in the afternoon hours. It was found that when the olouds developed sufficiently in the vertical direction to reach the height of the tropopause, gravity-wave oscillations in the vertical velocity above the tropopause would develop. The amplitude was 2 m/s, and the period was close to 6 min.Item Open Access Lessons learned observing Farley Buneman waves at low, middle, and high latitudes(Instituto Geofísico del Perú, 2008) Hysell, D. L.; Michhue, G.; Larsen, M. F.; Pfaff, R.; Chau Chong Shing, Jorge LuisDiapositivas presentadas en: ISEA 12 - 12th International Symposium on Equatorial Aeronomy, May 18-24, 2008. Crete, Greece.Item Open Access Onset conditions for equatorial spread F determined during EQUIS II(American Geophysical Union, 2005-12-22) Hysell, D. L.; Larsen, M. F.; Swenson, C. M.; Barjatya, A.; Wheeler, T. F.; Sarango, M. F.; Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge LuisAn investigation into the dynamics and layer structure of the postsunset ionosphere prior to the onset of equatorial spread F (ESF) took place during the NASA EQUIS II campaign on Kwajalein Atoll on August 7 and 15, 2004. On both nights, an instrumented rocket measured plasma number density and vector electric fields to an apogee of about 450 km. Two chemical release rockets were launched both nights to measure lower thermospheric wind profiles. The Altair UHF/VHF radar was used to monitor coherent and incoherent scatter. In both experiments, strong plasma shear flow was detected. Periodic, patchy bottom-type scattering layers were observed in the westward-drifting plasma below the shear nodes. The large-scale plasma depletions that formed later during ESF reproduced the periodic structure of the original, precursor layers. The layers were therefore predictive of the ESF that followed. We surmise that collisional shear instabilities may have given rise to large-scale plasma waves that were highlighted by the bottom- type layer structure and that preconditioned the postsunset ionosphere for ESF.Item Open Access Power spectra of oblique velocities in the troposphere and lower stratosphere observed at Arecibo, Puerto Rico(American Meteorological Society, 1986-07-26) Larsen, M. F.; Woodman Pollitt, Ronald Francisco; Sato, T.; Davis, M. K.Wind profiles measured with the Arecibo Observatory 430 MHz radar during 1979 and 1980 have been used to calculate frequency and radial wavenumber power spectra. Periods between 2 min and 6 h and vertical wavelengths between 300 m and 13.5 km are covered by the spectra. The data are line-of-sight velocity components obtained with a beam pointing between 5.4° and 15º off-vertical. The presented evidence supports the conclusion that the dominant contribution to the spectra at periods less than 1 h is from the vertical velocity component. The frequency spectra have spectral slopes near -1 for periods of less than 1 h, and the radial wavenumber spectra have slopes between -1 and -3/2. The results are discussed in the context of two-dimensional turbulence and a universal gravity-wave spectrum. We also present the spectra from an event associated with convection in the early evening hours. A strong peak in the spectral energy near the Brunt-Väisälä frequency was present during the convective activity. The energy content at longer periods was found to be enhanced in the ensuing period when the convective energy input at shorter time scales near the Brunt-Väisälä period had diminished.Item Open Access Rocket and radar investigation of background electrodynamics and bottom-type scattering layers at the onset of equatorial spread F(European Geosciences Union (EGU), 2006-07) Hysell, D. L.; Larsen, M. F.; Swenson, C. M.; Barjatya, A.; Wheeler, T. F.; Bullett, T. W.; Sarango, M. F.; Woodman Pollitt, Ronald Francisco; Chau Chong Shing, Jorge Luis; Sponseller, D.Sounding rocket experiments were conducted during the NASA EQUIS II campaign on Kwajalein Atoll designed to elucidate the electrodynamics and layer structure of the postsunset equatorial F region ionosphere prior to the onset of equatorial spread F (ESF). Experiments took place on 7 and 15 August 2004, each comprised of the launch of an instrumented and two chemical release sounding rockets. The instrumented rockets measured plasma number density, vector electric fields, and other parameters to an apogee of about 450 km. The chemical release rockets deployed trails of trimethyl aluminum (TMA) which yielded wind profile measurements. The Altair radar was used to monitor coherent and incoherent scatter in UHF and VHF bands. Electron density profiles were also measured with rocket beacons and an ionosonde. Strong plasma shear flow was evident in both experiments. Bottom-type scattering layers were observed mainly in the valley region, below the shear nodes, in westward-drifting plasma strata. The layers were likely produced by wind-driven interchange instabilities as proposed by Kudeki and Bhattacharyya (1999). In both experiments, the layers were patchy and distributed periodically in space. Their horizontal structure was similar to that of the large-scale plasma depletions that formed later at higher altitude during ESF conditions. We argue that the bottom-type layers were modulated by the same large-scale waves that seeded the ESF. A scenario where the large-scale waves were themselves produced by collisional shear instabilities is described.Item Restricted Shear flow effects at the onset of equatorial spread F(American Geophysical Union, 2006-11-23) Hysell, D. L.; Larsen, M. F.; Swenson, C. M.; Wheeler, T. F.Experiments were conducted during the NASA Equatorial Ionospheric Study (EQUIS) II sounding rocket campaign on Kwajalein Atoll to investigate the dynamics and stability of the postsunset equatorial F region ionosphere prior to the onset of equatorial spread F (ESF). Experiments took place on 7 and 15 August 2004, each composed of the launch of an instrumented and two chemical release sounding rockets. The instrumented rockets measured plasma number density, vector electric fields, and other parameters to an apogee of about 450 km. The chemical release rockets yielded lower thermospheric wind profile measurements. The Altair radar was used to monitor coherent and incoherent scatter in UHF and VHF bands. In both experiments, large‐scale waves preceded the emergence of ESF depletions and irregularities. We propose that the large‐scale waves were produced by a collisional shear instability. A three‐dimensional electrodynamic model is constructed that can reproduce the shear flow observed by the rockets. On the basis of the model, we calculate the linear growth rate for the collisional shear instability and show that it can compete with the generalized Rayleigh Taylor instability. A scenario where the former generates the large‐scale waves and initiates the latter is discussed.