Climatology of intermediate descending layers (or 150 km echoes) over the equatorial and low-latitude regions of Brazil during the deep solar minimum of 2009

Abstract. In this work, we have performed a study for the first time on the climatology of the intermediate descending layers (ILs) over Brazilian equatorial and low-latitude regions during the extreme solar minimum period of 2009. The result of this study shows that the occurrence frequency of the ILs is very high, being > 60 % over São Luís (2∘ S, 44∘ W; inclination: −3.8∘) and > 90 % in Cachoeira Paulista (22.42∘ S, 45∘ W; inclination: −33.5∘). In most cases the ILs occur during the day at altitudes varying from 130 to 180 km and they may descend to lower altitudes (∼100 km) in a time interval of a few minutes to hours. The main driving force for the ILs at the low-latitude region, may be considered to be the diurnal tide (24 h) followed in smaller dominance by the semidiurnal (12 h), terdiurnal (8 h) and quarter-diurnal (6 h) components. In the magnetic equatorial sector, similar behavior was seen, with the exception of the semidiurnal tide, which in general does not appear to have influenced the IL's dynamics (except in summer). Additionally, the IL mean descent velocity over São Luís and Cachoeira Paulista shows a day-to-day variability that may be associated with a wave-like perturbation with a periodicity of some days. Some peculiarities in the IL dynamics were noted, such as the presence of the ILs during the night hours. Ascending and descending ILs appeared to have been formed from some connection with the ionospheric F layer. Quite often, these characteristics are observed in the presence of strong signatures of the gravity wave propagation as suggested by the F layer traces in the ionogram. The descending intermediate layer over Brazil appears to have been formed through a process of F1 layer base detachment. An interesting case study showed that an ascending ILs, initially detected at ∼130 km, reached the base of the F2 layer, due probably to the gravity wave propagation and/or the effect of a prompt penetration electric field.

[1]  Hisao Takahashi,et al.  Seasonal characteristics of small- and medium-scale gravity waves in the mesosphere and lower thermosphere over the Brazilian equatorial region , 2018, Annales Geophysicae.

[2]  I. Batista,et al.  The influence of tidal winds in the formation of blanketing sporadic e-layer over equatorial Brazilian region , 2017 .

[3]  I. Batista,et al.  Simulations of blanketing sporadic E-layer over the Brazilian sector driven by tidal winds , 2017 .

[4]  I. Batista,et al.  Disturbance zonal and vertical plasma drifts in the Peruvian sector during solar minimum phases , 2016 .

[5]  A. Patra,et al.  On the linkage of daytime 150 km echoes and abnormal intermediate layer traces over Sanya , 2013 .

[6]  Jonathan T. Fentzke,et al.  Wave signatures in the midlatitude ionosphere during a sudden stratospheric warming of January 2010 , 2013 .

[7]  P. K. Rajesh,et al.  Modeling and observations of the low latitude ionosphere‐plasmasphere system at long deep solar minimum , 2012 .

[8]  P. Nogueira,et al.  Strong longitudinal difference in ionospheric responses over Fortaleza (Brazil) and Jicamarca (Peru) during the January 2005 magnetic storm, dominated by northward IMF , 2012 .

[9]  G. J. Bailey,et al.  Behaviour of the low-latitude ionosphere-plasmasphere system at long deep solar minimum , 2012 .

[10]  F. Rodrigues,et al.  On the characteristics of 150-km echoes observed in the Brazilian longitude sector by the 30 MHz São Luís radar , 2011 .

[11]  H. Le,et al.  The ionosphere under extremely prolonged low solar activity , 2011 .

[12]  Fabiano S. Rodrigues,et al.  A modeling study of foF2 and hmF2 parameters measured by the Arecibo incoherent scatter radar and comparison with IRI model predictions for solar cycles 21, 22, and 23 , 2011 .

[13]  V. S. Naidu,et al.  Daytime descending intermediate layers observed over a sub-tropical Indian station Waltair during low-solar activity period , 2010 .

[14]  P. Batista,et al.  Atmospheric tides and mean winds in the meteor region over Santa Maria (29.7°S; 53.8°W) , 2009 .

[15]  I. Batista,et al.  Equatorial evening prereversal vertical drift and spread F suppression by disturbance penetration electric fields , 2009 .

[16]  R. Heelis,et al.  Behavior of the O+/H+ transition height during the extreme solar minimum of 2008 , 2009 .

[17]  E. R. de Paula,et al.  Gravity wave initiation of equatorial spread F/plasma bubble irregularities based on observational data from the SpreadFEx campaign , 2009 .

[18]  W. Hocking,et al.  Observations of equatorial mesospheric winds over Cariri (7.4° S) by a meteor radar and comparison with existing models , 2008 .

[19]  A. Patra,et al.  Daytime 150‐km echoes observed with the Equatorial Atmosphere Radar in Indonesia: First results , 2008 .

[20]  A. Patra,et al.  Further investigations on 150-km echoing riddle using simultaneous observations of 150-km and E region echoes from off-electrojet location Gadanki , 2007 .

[21]  P. Batista,et al.  First observation of the diurnal and semidiurnal ocillation in the mesospheric winds over São João do Cariri-PB, Brazil , 2007 .

[22]  J. Chau,et al.  Statistics of 150-km echoes over Jicamarca based on low-power VHF observations , 2006 .

[23]  P. Batista,et al.  Structure of the mean winds and tides in the meteor region over Cachoeira Paulista, Brazil (22.7°S,45°W) and its comparison with models , 2004 .

[24]  S. Vadas,et al.  Thermospheric responses to gravity waves arising from mesoscale convective complexes , 2004 .

[25]  W. Ecklund,et al.  On a summer maximum in the occurrence frequency of 150 km (F1) radar echoes over Pohnpei , 2004 .

[26]  David L. Hysell,et al.  The São Luís 30 MHz coherent scatter ionospheric radar: System description and initial results , 2004 .

[27]  J. Liu,et al.  The intermediate layers and associated tidal motions observed by a digisonde in the equatorial anomaly region , 2003 .

[28]  P. E. Johnston,et al.  Equatorial 150‐km irregularities observed at Pohnpei , 1998 .

[29]  J. Mathews.  Sporadic E: current views and recent progress , 1998 .

[30]  R. Roble,et al.  Coupling mechanisms in the lower ionospheric-thermospheric system and manifestations in the formation and dynamics of intermediate and descending layers , 1995 .

[31]  R. Tsunoda.  Enhanced velocities and a shear in daytime Esq over Kwajalein and their relationship to 150 km echoes over the dip equator , 1994 .

[32]  G. J. Bailey,et al.  Modeling the formation of intermediate layers at Arecibo latitudes , 1994 .

[33]  Erhan Kudeki,et al.  High resolution observations of 150 km echoes at Jicamarca , 1993 .

[34]  R. Roble,et al.  Measurements and modelling of intermediate, descending, and sporadic layers in the lower ionosphere: Results and implications for global‐scale ionospheric‐thermospheric studies , 1992 .

[35]  J. Mathews,et al.  An upper E region quarterdiurnal tide at Arecibo , 1988 .

[36]  Bodo W. Reinisch,et al.  New techniques in ground‐based ionospheric sounding and studies , 1986 .

[37]  M. A. Abdu,et al.  Gravity wave induced ionization layers in the night F-region over Cachoeira Paulista (22°S, 45°W) , 1982 .

[38]  A. Rodger,et al.  The nocturnal intermediate layer over South Georgia , 1981 .

[39]  I. J. Kantor,et al.  Gravity wave induced ionization layers in the night F-region at low latitudes , 1980 .

[40]  J. Mathews,et al.  Upper atmosphere tides and the vertical motion of ionospheric sporadic layers at Arecibo , 1979 .

[41]  J. MacDougall.  Seasonal variation of semidiurnal winds in the dynamo region , 1978 .

[42]  J. S. Shen,et al.  Ionization layers in the nighttime E region valley above Arecibo , 1976 .

[43]  J. MacDougall.  110 km neutral zonal wind patterns , 1974 .

[44]  K. Fujitaka,et al.  A tidal theory of the ionospheric intermediate layer , 1973 .

[45]  B. Balsley.  Evidence of a stratified echoing region at 150 kilometers in the vicinity of the magnetic equator during daylight hours , 1964 .

[46]  J. Ratcliffe,et al.  Fine-Structure of the Ionosphere , 1933, Nature.

[47]  W. M. Goodall,et al.  Characteristics of the Ionosphere , 1933, Nature.