Shrinking equatorial plasma bubbles

Abstract

The formation of equatorial plasma bubbles (EPBs) associated with spread F irregularities are fairly common phenomenon in the postsunset equatorial ionosphere. These bubbles grow as a result of eastward polarization electric field resulting in upward E × B drift over the dip equator. As they grow they are also mapped to low latitudes along magnetic field lines. The EPBs are often observed as airglow depletions in the images of OI 630 nm emission. On occasions the growth of the features over the dip equator is observed as poleward extensions of the depletions in all‐sky images obtained from low latitudes. Herein, we present interesting observations of decrease in the latitudinal extent of the EPBs corresponding to a reduction in their apex altitudes over the dip equator. Such observations indicate that these bubbles not only grow but also shrink on occasions. These are the first observations of shrinking EPBs. The observations discussed in this work are based on all‐sky airglow imaging observations of OI 630.0 nm emission made from Panhala (11.1°N dip latitude). In addition, ionosonde observations made from dip equatorial site Tirunelveli (1.1°N dip latitude) are used to understand the phenomenon better. The analysis indicates that the speed of shrinking occurring in the topside is different from the bottomside vertical drifts. When the EPBs shrink, they might decay before sunrise hours.

Direct observational evidence for the merging of equatorial plasma bubbles

“…[] and followed in Narayanan et al . []. The results discussed herein are based on the observations from Panhala (16.8°N, 74.1°E; 11.1°N dip latitude) on 6 January 2008 and 3 and 5 February 2008 and those from Gadanki (13.5°N, 79.2°E; 6.5°N dip latitude) on 23 March 2009.…”

“…There have been reports revealing different directions of vertical plasma drift at different altitudes indicating pinching of the EPBs [ Laakso et al ., ]. On occasions, the EPBs were seen to shrink in their altitudinal extent over the dip equator [ Narayanan et al ., ].…”

Midlatitudinal Special Airglow Structures Generated by the Interaction Between Propagating Medium‐Scale Traveling Ionospheric Disturbance and Nighttime Plasma Density Enhancement at Magnetically Quiet Time

“…Here we propose the SGDI as a very possible mechanism to cause bifurcation of airglow depletion. Moreover, the northern EIA crest usually moves southward at nighttime (e.g., Narayanan et al, 2014Narayanan et al, , 2016Sun et al, 2017). The bifurcation would be generated by the SGDI when the eastward polarization electric field works on a northward sharp plasma gradient co-determined by the passing low plasma density within the airglow depletion of MSTID and the NPDE.…”

“…The MBWs frequently occur at the geographic equator, propagating poleward or equatorward and causing a reversal/abatement of meridional neutral winds (e.g., Colerico & Mendillo, 2002). The MBWs can also hold high plasma density to feed or erode the airglow depletions (e.g., Narayanan et al, 2014Narayanan et al, , 2016Sun et al, 2017). Thus the MBWs can be a source of NPDE.…”

Evolution processes of a group of equatorial plasma bubble (EPBs) simultaneously observed by ground‐based and satellite measurements in the equatorial region of China

“…Narayanan et al [] recently reported shrinking equatorial plasma bubbles. In their results, the poleward extension of the EPBs corresponds to the growth of the EPBs to higher apex altitudes and the equatorward collapse represents the shrinking of the EPBs toward lower apex height.…”