First Zonal Drift Velocity Measurement of Equatorial Plasma Bubbles (EPBs) From a Geostationary Orbit Using GOLD Data

The National Aeronautics and Space Administration (NASA) Global-scale Observations of the Limb and Disk (GOLD) satellite takes far-ultraviolet images of the Earth from geostationary orbit. GOLD observes the complete structure of equatorial plasma bubbles (EPBs). Since there are repeated observations of the same regions of the Earth, the zonal drift velocities of EPBs are derived using GOLD data. EPBs observed within 60-25 degrees W longitudes on 27-29 November 2018 are considered in the present analysis. The drift velocities obtained on 27 November 2018 are 116 4, 118 6, and 105 9 m/s at the North and South crests of equatorial ionization anomaly (EIA) and the magnetic equator, respectively. While on 29 November the velocities 107 10, 106 8, and 110 +/- 4 m/s are in agreement with the 27th (within the uncertainties), on 28 November the velocities are substantially lower: 80 +/- 3, 95 +/- 7, and 88 +/- 11 m/s. This is the first simultaneous measurement of EPB zonal drift velocities at both crests of EIA and the magnetic equator. On 27-29 November 2018, the average spacing between adjacent EPBs is found to be similar to 377, 526, and 442 km, respectively. Plain Language Summary After the sunset, the ionosphere becomes conducive to the formation of plasma irregularities. These irregularities are associated with depletions in the plasma density. In the images obtained from ground or space, these depleted regions look like elongated dark bands and are known as equatorial plasma bubbles (EPBs). The transionospheric radio wave propagation, satellite communication, and navigation systems are adversely affected by these bubbles. Thus, it is important to understand and investigate the formation and development of the plasma bubbles. These have been extensively studied using ground-based instruments and satellites. However, all of these techniques are limited to short time observations and small spatial coverage. NASA's Global-scale Observations of the Limb and Disk (GOLD) satellite has brought the unique opportunity to observe the Earth's complete disk continuously from the geostationary orbit. In the present study, zonal drift velocities of EPBs are derived from the data obtained by GOLD from geostationary orbit. Further, for the first time, EPB drift velocities are derived simultaneously at crests of the EIA and at the geomagnetic equator.