Causes of the longitudinal differences in the equatorial vertical E × B drift during the 2013 SSW period as simulated by the TIME‐GCM

Abstract

During stratospheric sudden warming (SSW) periods large changes in the low‐latitude vertical drift have been observed at Jicamarca as well as in other longitudinal sectors. In general, a strengthening of the daytime maximum vertical drift with a shift from prenoon to the afternoon is observed. During the January 2013 stratospheric warming significant longitudinal differences in the equatorial vertical drift were observed. At Jicamarca the previously reported SSW behavior prevails; however, no shift of the daytime maximum drift was exhibited in the African sector. Using the National Center for Atmospheric Research thermosphere‐ionosphere‐mesosphere electrodynamics general circulation model (TIME‐GCM) the possible causes for the longitudinal difference are examined. The timing of the strong SSW effect in the vertical drift (15–20 January) coincides with moderate geomagnetic activity. The simulation indicates that approximately half of the daytime vertical drift increase in the American sector may be related to the moderate geophysical conditions (Kp = 4) with the effect being negligible in the African sector. The simulation suggests that the wind dynamo accounts for approximately 50% of the daytime vertical drift in the American sector and almost 100% in the African sector. The simulation agrees with previous findings that the migrating solar tides and the semidiurnal westward propagating tide with zonal wave number 1 (SW1) mainly contribute to the daytime wind dynamo and vertical drift. Numerical experiments suggest that the neutral wind and the geomagnetic main field contribute to the presence (absence) of a local time shift in the daytime maximum drift in the American (African) sector.

The Comparison of Lunar Tidal Characteristics in the Low‐Latitudinal Ionosphere Between East Asian and American Sectors During Stratospheric Sudden Warming Events: 2009–2018

“…This suggests that the lunitidal effect is not only stronger but also tend to be prominent among the four tidal components in the American sector than in the East Asian sector during SSWs, especially in major events. With Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model simulation, Maute et al (2015) demonstrate that moderate geomagnetic conditions during the 2012-2013 SSW may introduce significant longitudinal differences in the daytime vertical drift enhancement between the American sector and the African sector. Qualitatively, the clarity of a TS signature indicates the relative importance of the TS-generating process compared to other driving factors.…”

“…Stening (2011) shows that the lunar tide of geomagnetic variations in the American sector (Huancayo, −12.0°S, −75.3°W) is much larger compared to the other sectors during SSWs. With Thermosphere-Ionosphere-Mesosphere Electrodynamics General Circulation Model, Maute et al (2015) indicate that the longitudinal difference of the TEC variations between American and African sectors may be caused by the different responses to the moderate geophysical conditions (Kp = 4), which accounts for approximately half of the daytime vertical drift increase in the American sector but is negligible in the African sector. Liu et al (2011) reported that the morning enhancement in TEC is significantly larger in the Peruvian sector than in the Asian sector, and the hemispheric asymmetry of the afternoon depletion is opposite in the two sectors.…”

“…Meanwhile, the SSW-related variations in the ionosphere exhibit longitudinal differences of which the causes are also not thoroughly understood (Anderson & Araujo-Pradere, 2010;Fang et al, 2012;Fejer et al, 2010;Goncharenko et al, 2013;Jonah et al, 2014;Liu et al, 2011;Maute et al, 2015;Mo & Zhang al., 2018;Siddiqui et al, 2017;Stening, 2011). Fejer et al (2010) illustrate that the onset of the morning enhancement in EEJ first appears in the American sector and several days later in the Indian and Japan sectors.…”

Evaluating Different Techniques for Constraining Lower Atmospheric Variability in an Upper Atmosphere General Circulation Model: A Case Study During the 2010 Sudden Stratospheric Warming

“…The SD nudging approaches of Maute et al () and J. C. Wang et al () were slightly different, but both constrained TIME‐GCM horizontal winds and neutral temperatures in an effort to study the lower atmospheric driving of the MLT and TI. Maute et al () constrained the zonal mean background atmosphere in the TIME‐GCM using hourly SD‐WACCM‐X output (i.e., WACCM‐X‐L116 was constrained using GEOS‐5), such that the zonal mean horizontal winds and neutral temperatures take the following form in the momentum and thermodynamic energy equations: where θ = latitude, or log pressure level ( p 0 =5 × 10 −7 hPa), t = time, represents zonal mean zonal ( ), and meridional ( ) winds, and the zonal mean temperature ( ) from TIME‐GCM ( ) and WACCM‐X‐L116/GEOS5 ( ), where the overbar represents a zonal average dynamical field. The fraction, α , is used to determine the relaxation time following Smith, Pedatella, et al (), which in the Maute et al () case is assumed to be 1.…”

Scientific challenges in thermosphere-ionosphere forecasting – conclusions from the October 2014 NASA JPL community workshop

“…The response of the thermosphere to geomagnetic forcing depends on the prior thermospheric conditions, which are largely determined by driving from below . Maute et al (2015) recently addressed the question with simulations representative of the conditions during a sudden stratospheric warming (SSW) in 2013, during which geomagnetic and tidal forcing acted at the same time. Tidal forcing, which originates from below the T-I, was found to create comparable effects to geomagnetic forcing, although the relative influences varied with longitude.…”