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

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.