The spread F Experiment (SpreadFEx): Program overview and first results

David C Fritts ,H Takahashi,C M Wrasse,P P Batista,P Stamus,B J Fechine,D M Riggin,M A Abdu,B R Batista,J H A Sobral,D Gobbi,F São Sabbas,I S Batista,B R Clemesha,F Kamalabadi,B Laughman,Bela G Fejer ,H L Liu ,Thomas Dautermann ,Lourivaldo Mota Lima ,Eurico De Paula ,Pierre-Dominique Pautet ,Sharon L Vadas ,A F Medeiros ,R A Buriti ,Jennifer S Haase ,Michael J Taylor

doi:10.1186/bf03353158

Abstract

Abstract We performed an extensive experimental campaign (the spread F Experiment, or SpreadFEx) from September to November 2005 to attempt to define the role of neutral atmosphere dynamics, specifically wave motions propagating upward from the lower atmosphere, in seeding equatorial spread F and plasma bubbles extending to higher altitudes. Campaign measurements focused on the Brazilian sector and included ground-based optical, radar, digisonde, and GPS measurements at a number of fixed and temporary sites. Related data on convection and plasma bubble structures were also collected by GOES 12 and the GUVI instrument aboard the TIMED satellite. Initial results of our analyses of SpreadFEx and related data indicate 1) extensive gravity wave (GW) activity apparently linked to deep convection predominantly to the west of our measurement sites, 2) the presence of small-scale GWactivity confined to lower altitudes, 3) larger-scaleGWactivity apparently penetrating to much higher altitudes suggested by electron density and TEC fluctuations in the E and F regions, 4) substantial GW amplitudes implied by digisonde electron densities, and 5) apparent direct links of these perturbations in the lower F region to spread F and plasma bubbles extending to much higher altitudes. Related efforts with correlative data are defining 6) the occurrence and locations of deep convection, 7) the spatial and temporal evolutions of plasma bubbles, the 8) 2D (height-resolved) structures of plasma bubbles, and 9) the expected propagation of GWs and tides from the lower atmosphere into the thermosphere and ionosphere.

Highlights

Considerable progress has been made in recent years in understanding the occurrence, morphology, and variability of equatorial spread F (ESF) and plasma bubbles penetrating to higher altitudes
Strong ESF and plasma bubbles typically arise during the pre-reversal enhancement (PRE) of the zonal electric field when upward E × B plasma drifts elevate the F layer sufficiently (Heelis et al, 1974; Fejer et al, 1999)
Increasing solar flux correlates with greater PREs of plasma drift, earlier ESF seeding and irregularity appearance, and higher initial altitudes (Hysell and Burcham, 2002)

Summary

Introduction

Considerable progress has been made in recent years in understanding the occurrence, morphology, and variability of equatorial spread F (ESF) and plasma bubbles penetrating to higher altitudes. An understanding of the conditions seeding ESF and plasma bubbles has remained elusive, with neither observations nor theory sufficiently comprehensive or persuasive to be definitive. Definitive proof of GW seeding, the “smoking gun”, observational or theoretical, has yet to be found These issues motivated a combined experimental, modeling, and theoretical program initiated with two field campaigns performed in Brazil during “moon down” conditions from September to November 2005. The primary goal of the spread F Experiment (SpreadFEx) was to test the theory that GWs play an essential role in the seeding of ESF and plasma bubbles extending to much higher altitudes. The purpose of this paper is to summarize our experimental design and describe our initial analysis results

Objectives

Results

Conclusion