Daytime ionospheric equatorial vertical drifts during the 2008–2009 extreme solar minimum

Abstract

One of the most interesting observations made by the Communication/Navigation Outage Forecasting System (C/NOFS) satellite mission was the detection of average equatorial ionospheric vertical drifts that largely differed from model predictions. C/NOFS measurements showed, in particular, downward drifts in the afternoon sector, and upward drifts around local midnight hours during the 2008 and 2009 extreme solar minimum. The unexpected behavior of the drifts has important implications for ionospheric modeling and suggests the necessity for a better understanding of the low‐latitude electrodynamics. We used ground‐based radar measurements to quantify the seasonal and solar flux variability of daytime equatorial drifts at lower altitudes (∼150 km) than those probed by C/NOFS (above ∼400 km). We found that average vertical drifts at 150 km altitude are in good agreement with model predictions of F region drifts and did not show the signatures of an enhanced semidiurnal pattern, as seen by C/NOFS. Comparison of the 150 km echo drifts with model predictions also shows that the increase (decrease) with height of the vertical drifts in the morning (afternoon) hours is a regular feature of the equatorial ionosphere. It occurred in all seasons and solar flux conditions between 2001 and 2011.

Long‐Term Estimation of Diurnal Vertical E × B Drift Velocities Using C/NOFS and Ground‐Based Magnetometer Observations

“…We wish to state that it has been shown previously that JULIA vertical E × B drift data correlate well with EEJ (e.g., Anderson et al, ) and have high agreement with ISR vertical E × B drift observations (Chau & Woodman, ; Kudeki & Fawcett, ). A clear historical perspective linking 150‐km echo Doppler velocities to equatorial vertical drifts along with relevant references has been presented in Rodrigues et al (). Ground‐based magnetometer data have advantage of being continuous with high temporal resolution and are available in a number of longitude sectors, thus increasing the probability of getting coincidental observations when the satellite is within the vicinity of the magnetometer location.…”

Unusual behavior of quiet-time zonal and vertical plasma drift velocities over Jicamarca during the recent extended solar minimum of 2008

“…A possible enhancement on the semidiurnal tide in low-latitude region was initially suggested as responsible for this unusual behavior of the vertical drift. Rodrigues et al (2015) did not observe this same characteristic in the daytime equatorial ionospheric vertical drifts as obtained from 150 km echoes over Jicamarca. As explained by them, the magnetic field lines that pass at 150 km altitude over the magnetic equator do not reach very far in latitude, so that the semidiurnal patterns similar to those found by Stoneback et al (2011) were not observed in the 150 km echo drifts.…”

Counter‐Electrojet Occurrence as Observed From C/NOFS Satellite and Ground‐Based Magnetometer Data Over the African and American Sectors

“…The rest of the CEJ occurrence rate is spread over other local times, but with afternoon CEJ occurrence being more predominant from C/NOFS observations. The presence of afternoon downward vertical drifts in C/NOFS vertical ion plasma drift data when the 150‐km echo drifts from the JULIA experiment showed largely upward drifts over Jicamarca has been reported (Rodrigues et al, ). Due to the altitude of the C/NOFS satellite, these afternoon downward drifts (CEJ in this case) were attributed to the possibility of increased magnitude of semidiurnal tides in the topside ionosphere (Stoneback et al, ; Rodrigues et al, ).…”

“…While this is mostly evident, a specific example in Figure b is for the case of 1500–1600 LT where CEJ occurrence identified by C/NOFS data is more than double the corresponding result for magnetometer observations. Using radar and C/NOFS data sets during 2008–2009 over Jicamarca, Rodrigues et al () observed that the C/NOFS afternoon downward vertical drift values did not feature in the 150‐km echoes, which by inference may be true for Δ H as both JULIA and Δ H observations are all approximately within the E region (e.g., Anderson et al, ). In particular, we note that the percentage CEJ occurrences from magnetometer‐derived Δ H is either less than 20% or absent during local times 1000–1600 LT for both 2008–2010 and 2011–2014.…”

“…Since the CEJ's first detection (Gouin, ), various studies have investigated the CEJ occurrence based mainly on magnetometers deployed in equatorial and/or low‐latitude regions (e.g., Alex & Mukherjee, ; Rastogi, , and references therein). With time, the emergence of Low Earth Orbit (LEO) satellites in conducting ionosphere‐thermosphere investigations such as Magnetic Field Satellite, Republic of China Satellite, Challenging Minisatellite Payload (CHAMP), Communications and Navigation Outage Forecasting System (C/NOFS), and SWARM, LEO measurements became complementary data sources for EEJ or CEJ studies (e.g., Cohen & Achache, ; Fejer & Scherliess, ; Fejer et al, ; Kumar et al, ; Lühr et al, ; Rodrigues et al, ; Yizengaw & Groves, ; Zhou et al, ). CEJ studies can also be performed using Incoherent Scatter Radar over Jicamarca or the mode that operates to determine E region irregularities commonly known as the Jicamarca Unattended Long‐Term Studies of Ionosphere and Atmosphere (JULIA) and similar coherent radar measurements in other longitude regions such as the Indian and Indonesian sectors (Patra et al, , ).…”