Equatorial Ionospheric Scintillations and Zonal Irregularity Drifts Observed with Closely-Spaced GPS Receivers in Indonesia

Abstract

To investigate drift velocities of a few hundred meter-scale irregularities associated with equatorial plasma bubbles, we used three single-frequency GPS receivers at the Equatorial Atmosphere Radar (EAR) site at Kototabang, Indonesia (0.20 S, 100.32 E; geomagnetic latitude 10.6 S), since January 2003. The GPS receivers sampled GPS signal intensity at a rate of 20 Hz. Distances between the receivers were 116, 127, and 152 m. An analysis of scintillation index ðS 4 Þ in two years (2003)(2004) revealed that the scintillations often occurred between 2000-0100 LT at equinoxes and that their occurrence rate was higher during March-April than during September-October. Drift velocities of irregularities were measured using cross-correlation analysis with the time series of the GPS signal intensity obtained from the three receivers. From a statistical analysis of the drift velocities, the eastward component of drift velocity just after sunset is found to be greater during March-April than during September-October. Based on these results, for the first time, we suggest that the east-west component of plasma drift velocity (or vertical electric field) may be related to the evolution of plasma irregularities causing scintillations throughout the mechanism causing the prereversal enhancement of the eastward electric fields. The equinoctial asymmetry of the drift velocity could be attributed to the equinoctial asymmetry of neutral winds in the thermosphere.

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

“…3 and 4, the prevailing characteristic of the mean irregularity zonal drift velocities over Cachoeira Paulista during the equinoxes and December solstice months is the reduction in the amplitude of the eastward velocities with the progression of night. This behavior is in agreement with earlier observations reported at equatorial and low-latitude regions (e.g., Otsuka et al, 2006;Muella et al, 2013Muella et al, , 2014Liu et al, 2015). According to theoretical formulations, this is a direct result of the post-sunset weakening of the vertical electric fields mapped to off-equatorial latitudes.…”

Low-latitude scintillation occurrences around the equatorial anomaly crest over Indonesia

“…At both Bandung and Pontianak (in our cases), the 400 mscale irregularities causing GPS scintillations disappear at approximately 01:00 LT, and this result is consistent with previous studies (Basu et al, 1978;Otsuka et al, 2006). Our result related to these post-sunset scintillation occurrences can be ascribed to equatorial plasma bubbles.…”

Propagation characteristics of nighttime mesospheric and thermospheric waves observed by optical mesosphere thermosphere imagers at middle and low latitudes

“…It is not clear how these two types of waves are coupled poleward of the anomaly. Other than these waves, distinct airglow depletions caused by equatorial plasma bubbles are often observed at Kototabang, Sata, Darwin, and even Shigaraki (e.g., Otsuka et al, 2002Otsuka et al, , 2006Shiokawa et al, 2004;Ogawa et al, 2005).…”