Equatorial plasma bubbles and L-band scintillations in Africa during solar minimum

Abstract. We report on the longitudinal, local time and seasonal occurrence of equatorial plasma bubbles (EPBs) and L band (GPS) scintillations over equatorial Africa. The measurements were made in 2010, as a first step toward establishing the climatology of ionospheric irregularities over Africa. The scintillation intensity is obtained by measuring the standard deviation of normalized GPS signal power. The EPBs are detected using an automated technique, where spectral analysis is used to extract and identify EPB events from the GPS TEC measurements. Overall, the observed seasonal climatology of the EPBs as well as GPS scintillations in equatorial Africa is adequately explained by geometric arguments, i.e., by the alignment of the solar terminator and local geomagnetic field, or STBA hypothesis (Tsunoda, 1985, 2010a). While plasma bubbles and scintillations are primarily observed during equinoctial periods, there are longitudinal differences in their seasonal occurrence statistics. The Atlantic sector has the most intense, longest lasting, and highest scintillation occurrence rate in-season. There is also a pronounced increase in the EPB occurrence rate during the June solstice moving west to east. In Africa, the seasonal occurrence shifts towards boreal summer solstice, with fewer occurrences and shorter durations in equinox seasons. Our results also suggest that the occurrence of plasma bubbles and GPS scintillations over Africa are well correlated, with scintillation intensity depending on depletion depth. A question remains about the possible physical mechanisms responsible for the difference in the occurrence phenomenology of EPBs and GPS scintillations between different regions in equatorial Africa.

[1]  L. C. Gentile,et al.  Longitudinal variability of equatorial plasma bubbles observed by DMSP and ROCSAT‐1 , 2004 .

[2]  Paul M. Kintner,et al.  Equatorial plasma bubbles in the ionosphere over Eritrea: occurrence and drift speed , 2006 .

[3]  R. Tsunoda.  On equatorial spread F: Establishing a seeding hypothesis , 2010 .

[4]  P. J. Sultan,et al.  Linear theory and modeling of the Rayleigh‐Taylor instability leading to the occurrence of equatorial spread F , 1996 .

[5]  F. S. Johnson,et al.  Occurrence of equatorial F region irregularities: Evidence for tropospheric seeding , 1998 .

[6]  James A. Secan,et al.  Equatorial scintillation and systems support , 1997 .

[7]  J. Retterer,et al.  Modeling the climatology of equatorial plasma bubbles observed by DMSP , 2009 .

[8]  L. C. Gentile,et al.  Equatorial plasma bubbles observed by DMSP satellites during a full solar cycle: Toward a global climatology , 2002 .

[9]  Larry J. Paxton,et al.  Control of equatorial ionospheric morphology by atmospheric tides , 2006 .

[10]  Keith M. Groves,et al.  The GPS Segment of the AFRL-SCINDA Global Network and the Challenges of Real-Time TEC Estimation in the Equatorial Ionosphere , 2006 .

[11]  Ronald F. Woodman,et al.  Equatorial spread F: Implications of VHF radar observations , 1970 .

[12]  Patricia H. Doherty,et al.  Ionospheric Scintillation Effects on Single and Dual Frequency GPS Positioning , 2003 .

[13]  Roland T. Tsunoda,et al.  On seeding equatorial spread F during solstices , 2010 .

[14]  David L. Hysell,et al.  Collisional shear instability in the equatorial F region ionosphere , 2004 .

[15]  Jules Aarons,et al.  The longitudinal morphology of equatorial F-layer irregularities relevant to their occurrence , 1993 .

[16]  R. Heelis,et al.  Seasonal and longitudinal variation of large-scale topside equatorial plasma depletions , 2005 .

[17]  B. Reinisch,et al.  Conjugate Point Equatorial Experiment (COPEX) Campaign in Brazil: Electrodynamics highlights on spread F development conditions and day-to-day variability , 2009 .

[18]  J. A. Whalen,et al.  The linear dependence of GHz scintillation on electron density observed in the equatorial anomaly , 2009 .

[19]  R. Tsunoda,et al.  Control of the seasonal and longitudinal occurrence of equatorial scintillations by the longitudinal gradient in integrated E region Pedersen conductivity , 1985 .

[20]  James A. Secan,et al.  An improved model of equatorial scintillation , 1995 .

[21]  Keith M. Groves,et al.  Temporal Decorrelation of GPS Satellite Signals due to Multiple Scattering from Ionospheric Irregularities , 2010 .

[22]  Georgios Balasis,et al.  Magnetic signatures of equatorial spread F as observed by the CHAMP satellite , 2006 .

[23]  J. A. Whalen,et al.  An equatorial bubble: Its evolution observed in relation to bottomside spread F and to the Appleton anomaly , 2000 .

[24]  Ronald F. Woodman,et al.  Radar observations of F region equatorial irregularities , 1976 .

[25]  R. W. Weight,et al.  Equatorial spread-F , 1959 .

[26]  G. Seemala,et al.  Statistics of total electron content depletions observed over the South American continent for the year 2008 , 2011 .

[27]  W. J. Burke,et al.  A global climatology for equatorial plasma bubbles in the topside ionosphere , 2006 .

[28]  P. Doherty,et al.  The Low-Latitude Ionosphere Sensor Network (LISN) , 2009 .

[29]  R. Woodman,et al.  Seeding and layering of equatorial spread F by gravity waves , 1990 .

[30]  R. Cohen,et al.  The interpretation and synthesis of certain spread‐F configurations appearing on equatorial ionograms , 1961 .

[31]  S. Basu,et al.  High resolution topside in situ data of electron densities and VHF/GHz scintillations in the equatorial region , 1983 .

[32]  B. L. Cragin,et al.  Bottomside sinusoidal irregularities in the equatorial F region , 1983 .

[33]  E. Araujo‐Pradere,et al.  Comparing daytime, equatorial E◊B drift velocities and TOPEX/TEC observations associated with the 4-cell, non-migrating tidal structure , 2009 .