Investigation of ionospheric precursors leading to spread F during the EQUIS II campaign on Kwajalein.

Details Investigation of ionospheric precursors leading to spread F during the EQUIS II campaign on Kwajalein. Investigation of ionospheric precursors leading to spread F during the EQUIS II campaign on Kwajalein.

May 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsa23b..04h&link_type=abstract

American Geophysical Union, Spring Meeting 2005, abstract #SA23B-04

Computer Science

Sound

2415 Equatorial Ionosphere, 2435 Ionospheric Disturbances, 2439 Ionospheric Irregularities, 2471 Plasma Waves And Instabilities

Scientific paper

A sounding rocket investigation of bottom-type scattering layers, shear flow, and the factors which may precondition the equatorial F region ionosphere for postsunset instability was carried out in August, 2004 from the Roi Namur range during the EQUIS II campaign on Kwajalein Atoll. Identical experiments were performed on August 7 and 15, each comprised of the launch of an instrumented payload which measured plasma number density and vector electric field profiles along with two chemical release payloads. The latter deployed TMA trails from which vector neutral wind profiles in three locations could be deduced. Ground-based support was provided by the Altair radar, a dual-frequency radar capable of measuring both coherent and incoherent scatter. The purpose of the experiment was 1) to understand and quantify the vertical shear in the zonal plasma drift that occurs each day around sunset, 2) to understand the nature of the bottom-type scattering layers that inhabit westward-drifting strata in the bottomside F region and that serve as precursors for fully developed spread F, and 3) to understand the influence of shear flow on the postsunset ionosphere. Ground-based and in situ data confirm the presence of strong shear in the flow proceeding the emergence of spread F irregularities in both experiments. The bottom-type layers that formed exhibited properties consistent with horizontal wind-driven gradient drift instabilities growing in an inhomogeneous bottomside. Regular 30-50 km structuring similar to what has been observed recently at Jicamarca was also evident in the layers. This structuring was repeated in the spread F depletions that finally appeared. The structuring of the bottom-type layers therefore served as a telltale of the spread F irregularities to come. Moreover, the structuring may have been produced by shear instabilities as described recently by Hysell and Kudeki [2004]. Numerical modeling of the causes of the shear as well as its effects on stability may therefore point the way to a spread F forecast strategy.

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