A dayside plasma depletion observed at midlatitudes during quiet geomagnetic conditions

Abstract

In this study we investigate a dayside, midlatitude plasma depletion (DMLPD) encountered on 22 May 2014 by the Swarm and GRACE satellites, as well as ground‐based instruments. The DMLPD was observed near Puerto Rico by Swarm near 10 LT under quiet geomagnetic conditions at altitudes of 475–520 km and magnetic latitudes of ∼25°–30°. The DMLPD was also revealed in total electron content observations by the Saint Croix station and by the GRACE satellites (430 km) near 16 LT and near the same geographic location. The unique Swarm constellation enables the horizontal tilt of the DMLPD to be measured (35° clockwise from the geomagnetic east‐west direction). Ground‐based airglow images at Arecibo showed no evidence for plasma density depletions during the night prior to this dayside event. The C/NOFS equatorial satellite showed evidence for very modest plasma density depletions that had rotated into the morningside from nightside. However, the equatorial depletions do not appear related to the DMLPD, for which the magnetic apex height is about 2500 km. The origins of the DMLPD are unknown, but may be related to gravity waves.

Daytime midlatitude plasma depletions observed by Swarm: Topside signatures of the rocket exhaust

“…As a reference, the Swarm observations on 22 May 2014 reported Park et al [] are presented in Figures h–j. All Swarm observations were made around 14:00 UT (1000 LT).…”

“…Abnormal daytime midlatitude plasma depletions (DMLPDs) were detected over the northern Atlantic Ocean on 22 May 2014 by the Swarm constellation and the Gravity Recovery and Climate Experiment (GRACE) satellite [ Park et al , ]. The DMLPDs had latitudinal and longitudinal widths of about 300–400 km and 1000 km, respectively.…”

“…The DMLPDs had latitudinal and longitudinal widths of about 300–400 km and 1000 km, respectively. Park et al [] tried to explain the DMLPD phenomena in association with some natural phenomena, but they could not clarify the source of the DMLPDs with the limited data set. Similar DMLPDs were detected again over northern Atlantic Ocean on 20 May 2015 by the Swarm constellation.…”

ULF wave power features in the topside ionosphere revealed by Swarm observations

“…In general, the inclusion of the electron density recordings helps to identify time segments of the signal that contain signatures of postsunset equatorial spread F (ESF) events [ Stolle et al , ] and therefore discriminate between Pc3 wave and plasma depletion occurrence. However, Park et al [] have recently demonstrated using Swarm data that plasma depletion events can also occur on the dayside making the addition of the PLP data also useful for dayside tracks although in our case there is no evidence of such events. Prominent compressional Pc3 activity is observed around the equator between −30° and +30° as well as at latitudes higher than ±60°.…”

Calibration and Validation of Swarm Plasma Densities and Electron Temperatures Using Ground‐Based Radars and Satellite Radio Occultation Measurements

“…The TIIs have been designed to measure 3‐D ion drift velocities and ion temperatures, and LPs provide ion density from the high‐gain probe (during the negatively biased portion of the sweep) and T e from both high‐ and low‐gain probes with a 2 Hz resolution. Recently, several studies have used preliminary, level 1B Swarm LP data to investigate various physical phenomena in the ionosphere (Buchert et al, ; Goodwin et al, ; Park et al, , ). Although initial results to validate these data have been presented by several authors (Lomidze et al, ; Palin et al, ; Pedatella et al, ), the calibration and validation of these data require more complete study and thorough data analysis.…”