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Guará High Altitude Spread F
Launch date: 14 October, 1994
Launch time: 21:55 UTÊ (19:55 Local Time)
Participating institutions: LaBelle, Jahn, Trimpi (Dartmouth); Swartz, Alcala (Cornell); Pfaff (Goddard Space Flight Center); Baker, Jenson (Utah State); Sobral, Abdu, dePaula, Muralikrishna (Brazilian National Institute of Space Research)
Vehicle apogee: 957km
Location: Alcantara, Brazil (2.3¡ S, 44.4¡ W) (65.13¡ N, 147.48¡ W)
Instrument list: Electric Field (DC and Wave), Langmuir Probe (Electron Density), Low Frequency Active Plasma Resonance Probe, Capacitance Probe (from INPE), Dual Frequency GPS (Ground Based)
The goal of the Dartmouth College rocket experiment in Brazil was to measure the electric field and the density of the charged particles as a function of space and time within a turbulent Equatorial Spread-F storm over a larger altitude range than ever before probed in an equatorial rocket or satellite experiment.
Equatorial spread-F (ESF) is a dramatic nighttime plasma instability phenomenon typical for Earth's equatorial ionosphere. It produces structures at scales from more than 1000 km to less than 10 cm. The altitude ranges covered by spread-F can at times exceed 1000 km. In October 1994 a NASA/Dartmouth sounding rocket was launched from Brazil to carry a payload into high-altitude spread-F conditions. Data from this flight provide the first in situ measurements within spread-F above 600 km altitude. Collisional effects in this region are negligible, much in contrast to lower altitudes where we have to look at the problem in a collisional context. Based on the rocket measurements our research tries to provide an understanding of high-altitude spread-F, particular in comparison to the wealth of results gained at lower altitudes.
The Guara spread F rocket provides accurate electric field measurements up to 900 km in and above equatorial spread F for the first time. The polarization field within the plasma bubbles is also measured and agrees with theoretical expectations. See Jahn et al., 1997, for details.
The large scale spectrum of density irregularities encountered by the Guara rocket shows features in common with previous measurements as well as excellent correlation with simultaneous radar data. From the radar data, it was possible to estimate or at least put bounds on the age of turbulent features intercepted by the rocket. The irregularity spectra associated with these features showed evidence of scale-independent decay of the irregularities, which agrees with some previous indirect experimental evidence and theoretical predictions. See LaBelle et al., 1997, for details.
Dartmouth operated a dual-frequency GPS receiver borrowed from UNAVCO during the two-week Guara campaign. NOAA contributed to the data analysis. By parameterizing TEC fluctuations on lines-of-sight to multiple satellites simultaneously over 6-8 hours each evening, and making the assumption that the large scale turbulence is field aligned, we produced images of the equatorial turbulence in the east-west plane as a function of time. These images clearly showed patches of turbulence associated with spread F bubbles drifting west to east across the sky. Reasonable drift velocities could be inferred from these images. See Musman et al., 1997, for details.
Dartmouth also helped support optical all-sky camera observations on several wavelengths made by Mike Taylor of Utah State University for the two-week campaign. Many clear nights and excellent signal to noise of the camera system allowed detection of equatorial spread F plasma bubbles and measurements of their drift velocities. See Taylor et al., 1997, for details.
The rocket electron density and electric field data have been spectrally analyzed, and with effort, the resulting spectra have been parameterized as a function of altitude for both upleg and downleg of the flight. Scatter plots of these parameters show the absence of an altitude transition to "inertial regime" turbulence as predicted by theory, despite the high altitude of the event penetrated by the rocket. Possibly the relatively low amplitude of the turbulence prevented the onset of inertial regime physics. See Jahn et al., 1998, for details.
Selected Data | Top
This radar map shows the ionospheric storm into which the Dartmouth rocket was launched on October 14, 1994 Dark shades indicate regions of intense turbulence in the ionosphere detected by the radar. A solid line shows the estimated trajectory of the rocket through this turbulence. The two traces at right show the charged particle density measured by the rocket as a function of altitude on its upleg and downleg. During the time when the rocket penetrated the storm, it encountered highly irregular fluctuating charged particle densities. It is these charged particle density irregularities which cause the pernicious effects associated with Equatorial Spread F, such as interruptions in radio communications. The details of these electron density fluctuations are under study at Dartmouth.
Photos | Top
Note: Photos courtesy of NASA Wallops Flight Facility.
Publications | Top
54. Jahn, J.-M., J. LaBelle, and R.A. Treumann, Evaluating the stationarity of equatorial spread F time series data, J. Atmos. Solar-Terr. Phys., 59, 439, 1997.
55. Jahn, J.-M., J. LaBelle, J.H.A. Sobral, T. Aggson, and W.B. Hanson, Simultaneous detection of an equatorial spread F bubble by ground-based photometers and the San Marco-5 satellite, J. Atmos. Solar-Terr. Phys., 59, 1601, 1997.
57. LaBelle, J., J.M. Jahn, R.F. Pfaff, W.E. Swartz, J.H.A. Sobral, M.A. Abdu, P. Muralikrishna, and E. dePaula, The Brazil/Guará campaign equatorial spread F experiment: Large-scale results, Geophys. Res. Lett., 24, 1691, 1997.
58. Musman, S., J.M. Jahn, J. LaBelle, and W.E. Swartz, Imaging spread-F structures using GPS observations at Alcantara, Brazil, Geophys. Res. Lett., 24, 1703, 1997.
59. Jahn, J.M., J. LaBelle, and R.F. Pfaff, Electric field measurements from the Brazil/Guará spread F rocket, Geophys. Res. Lett., 24, 1695, 1997.
60. Taylor, M.J., J.V. Eccles, J. LaBelle, and J.H.A. Sobral, High resolution OI (630 nm) image measurements of F-region depletion drifts during the Guará campaign, Geophys. Res. Lett., 24, 1699, 1997.
61. Pfaff, R.F., J.H.A. Sobral, M.A. Abdu, W.E. Swartz, J. LaBelle, M. Larsen, and R. Goldberg, The Guará campaign: A series of rocket-radar investigations of the Earth's upper atmosphere at the magnetic equator, Geophys. Res. Lett., 24, 1666, 1997.
67. Jahn, J.M., and J. LaBelle, Rocket measurements of high-altitude spread F irregularities and the magnetic equator, J. Geophys. Res., 103, 23427, 1998.
Note: Numbers refer to Full Publication List
Also Note: Most abstracts are freely available through NASA's Astrophysics Data System Bibliographic Services (ADS). Some are available locally. Full texts are only available to users within institutions that subscribe to the corresponding web-based journal.