The causal relationship between plasma bubbles and blobs in the low‐latitude F region during a solar minimum

Abstract

Plasma density depletions (bubbles) and enhancements (blobs) with respect to the background ionosphere occur at night in the low-latitude F region. Those phenomena are understood to be either causally linked or independent. The idea of the causal relationship between bubbles and blobs is on the basis of the observations of them in the same longitude. However, the occurrence of bubbles and blobs in the same longitude can also be just a coincidence. We investigate causal linkage of bubbles and blobs using the measurements of the ion density on 5 days in June 2008 and April 2009 by the Communication/Navigation Outage Forecasting System and CHAllenging Minisatellite Payload satellites. The observations during the solar minimum show that blobs occur in broader longitudes than do bubbles and occur in any longitudes regardless of the existence of bubbles. These observations indicate that a significant portion of blobs are not associated with bubbles. Even if some blobs are associated with bubbles, those blobs are indistinguishable from those produced by other sources. Therefore, the observations of bubbles and blobs at the same longitudes do not warrant their causal relationship. The independent behavior of bubbles and blobs rather indicates that their occurrences in the same longitudes are mostly coincidences. Considering the frequent occurrence of blobs near midnight, June solstice, and the solar minimum, medium-scale traveling ionospheric disturbances are likely the major source of blobs. This idea is supported by the observations of blobs with the ionospheric disturbances in broad longitudes and latitudes.

Plasma Blobs Associated With Medium‐Scale Traveling Ionospheric Disturbances

“…Numerical simulations have also shown the formation of blobs when bubbles develop , Krall, Huba, Ossakow, et al, 2010. However, the detection of blobs in the absence of bubbles indicates that bubbles are not a prerequisite for the development of blobs (Kil, Choi, et al, 2011, 2015. The idea of the MSTID-blob connection is supported by the observations of blobs at the locations of MSTIDs (Kil & Paxton, 2017;Miller et al, 2014) and some similarities in the occurrence climatology of blobs and MSTIDs (Choi et al, 2012;Haaser et al, 2012).…”

Global Distribution of Nighttime Medium‐Scale Traveling Ionospheric Disturbances Seen by Swarm Satellites

“…Plasma bubbles and blobs represent plasma depletions and enhancements, respectively, relative to the ambient plasma density. The creation of plasma blobs in middle latitudes is explained in association with either equatorial plasma bubbles (Huang et al, ; Krall et al, , ; Le et al, ; Martinis et al, ; Yokoyama et al, ) or MSTIDs (Choi et al, ; Kil et al, , ; Miller et al, ), but we do not know yet which mechanism plays a dominant role in the creation of blobs.…”

Review of Long-Term Trends in the Equatorial Ionosphere Due the Geomagnetic Field Secular Variations and Its Relevance to Space Weather

“…This, in combination with the pre-reversal enhancement in the upward plasma drift, causes the plasma to become unstable, and the EPB grows and propagates upward. EPBs under certain conditions, can also induce plasma blobs (plasma density enhancements with respect to the background ionosphere) [26,27]. They both affect radio signals and can sometimes degrade and disrupt communications and navigation systems, which turns them into an important space weather concern.…”