Equatorial plasma bubbles in the ionosphere over Eritrea: occurrence and drift speed

An all-sky imager was installed in Asmara, Eritrea (15.4° N, 38.9° E, 7° N dip) and used to monitor the OI 630-nm nightglow. Nine months of data were studied between September 2001 and May 2002, a time including the recent maximum in the solar activity cycle. Equatorial plasma bubbles (EPBs) were recorded on 63% of nights with adequate viewing conditions. The station location within view of the equatorial ionization anomaly and with a magnetic declination near zero makes it an excellent test case for comparison with satellite studies of the seasonal variation of EPBs with longitude. The imager was accompanied by two Cornell GPS scintillation monitors, and the amplitude scintillation data are compared to the all-sky data. GPS scintillations indicate the beginning of EPBs, but die out sooner in the post-midnight period than the larger scale EPBs. Both phenomena exhibit clear occurrence maxima around the equinoxes. Ionospheric zonal drift speeds have been deduced from EPB and GPS scintillation pattern movement. Average near-midnight EPB drift speeds are between 100 and 120 m/s most months, with the GPS scintillation speeds being about the same. A winter drift speed maximum is evident in both EPB and GPS scintillation monthly means.

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

[2]  Ronald F. Woodman,et al.  F region east‐west drifts at Jicamarca , 1981 .

[3]  H. Takahashi,et al.  Plasma bubble zonal velocity variations with solar activity in the Brazilian region , 2004 .

[4]  C. Reddi.  MIDDLE ATMOSPHERE DYNAMICS , 1998 .

[5]  Paul M. Kintner,et al.  Development and use of a GPS ionospheric scintillation monitor , 2001, IEEE Trans. Geosci. Remote. Sens..

[6]  L. C. Gentile,et al.  DMSP observations of equatorial plasma bubbles in the topside ionosphere near solar maximum , 2001 .

[7]  H. Takahashi,et al.  Ionospheric plasma bubble zonal drifts over the tropical region: a study using OI emission all-sky images , 2003 .

[8]  Larry J. Paxton,et al.  F‐region plasma distribution seen from TIMED/GUVI and its relation to the equatorial spread F activity , 2004 .

[9]  Hiroshi Oya,et al.  Occurrence Characteristics of Low Latitude Ionosphere Irregularities Observed by Impedance Probe on Board the Hinotori Satellite , 1986 .

[10]  R. Wiens,et al.  Brightness variations of the northern 630nm intertropical arc and the midnight pressure bulge over Eritrea , 2004 .

[11]  T. Tsuda,et al.  Gravity waves and ionospheric irregularities over tropical convection zones observed by GPS/MET Radio Occultation , 2001 .

[12]  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 .

[13]  B. Ledvina,et al.  Analysis of the seasonal variations of equatorial plasma bubble occurrence observed from Haleakala, Hawaii , 2004 .

[14]  Paul M. Kintner,et al.  Global Positioning System measurements of the ionospheric zonal apparent velocity at Cachoeira Paulista in Brazil , 2000 .

[15]  B. M. Pathan,et al.  Seasonal and solar cycle association of zonal drifts of ionospheric plasma irregularities in the Indian equatorial region , 1996 .

[16]  B. Tinsley.  Images of transequatorial F region bubbles in 630- and 777-nm emissions compared with satellite , 1997 .

[17]  Harald U. Frey,et al.  Determination of low latitude plasma drift speeds from FUV images , 2003 .

[18]  K. Yeh,et al.  Radio wave scintillations in the ionosphere , 1982 .

[19]  Takashi Maruyama,et al.  Longitudinal variability of annual changes in activity of equatorial spread F and plasma bubbles , 1984 .

[20]  P. Fagundes,et al.  Height-resolved ionospheric drifts at low latitudes from simultaneous OI 777.4 nm and OI 630.0 nm imaging observations , 2004 .

[21]  Paul M. Kintner,et al.  Latitudinal variations of scintillation activity and zonal plasma drifts in South America , 2002 .

[22]  G. Haerendel,et al.  Theory for modeling the equatorial evening ionosphere and the origin of the shear in the horizontal plasma flow , 1992 .

[23]  B. Ledvina,et al.  Understanding spaced-receiver zonal velocity estimation , 2004 .

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

[25]  G. K. Mukherjee.  Studies of equatorial F-region depletions and dynamics using multiple wavelength nightglow imaging , 2003 .

[26]  S. Basu,et al.  The multi‐instrumented studies of equatorial thermosphere aeronomy scintillation system: Climatology of zonal drifts , 1996 .

[27]  L. C. Gentile,et al.  Seasonal-longitudinal variability of equatorial plasma bubbles , 2004 .