skip to main content

Title: Dynamic Drivers of TIFe Diurnal Cycle in Antarctica
The discovery of the thermosphere-ionosphere Fe (TIFe) layers has opened a door to exploring the least understood thermosphere and ionosphere region between 100 and 200 km with ground-based lidar instruments. The characteristics of the polar TIFe layers, and the impacts of the atmosphere neutral dynamics, electrodynamics, and metallic chemistry on the formation of TIFe layers deserve further investigation, especially the diurnal cycles of TIFe layers observed by lidar. This paper aims at investigating the major driving forces with 1-D Thermosphere-Ionosphere Fe/Fe + (TIFe) model. A main question to answer is whether neutral dynamics like tidal winds or electrodynamics like the convection electric fields and currents in the magnetosphere and ionosphere are responsible for the diurnal cycle of TIFe layers.  more » « less
Award ID(s):
Author(s) / Creator(s):
; ; ; ; ; ; ; ;
Date Published:
Journal Name:
EPJ Web of Conferences
Page Range / eLocation ID:
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    A dramatic thermospheric temperature enhancement and inversion layer (TTEIL) was observed by the Fe Boltzmann lidar at McMurdo, Antarctica during a geomagnetic storm (Chu et al. 2011, The Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (TIEGCM) driven by empirical auroral precipitation and background electric fields cannot adequately reproduce the TTEIL. We incorporate the Defense Meteorological Satellite Program (DMSP)/Special Sensor Ultraviolet Spectrographic Imager (SSUSI) auroral precipitation maps, which capture the regional‐scale features into TIEGCM and add subgrid electric field variability in the regions with strong auroral activity. These modifications enable the simulation of neutral temperatures closer to lidar observations and neutral densities closer to GRACE satellite observations (~475 km). The regional scale auroral precipitation and electric field variabilities are both needed to generate strong Joule heating that peaks around 120 km. The resulting temperature increase leads to the change of pressure gradients, thus inducing a horizontal divergence of air flow and large upward winds that increase with altitude. Associated with the upwelling wind is the adiabatic cooling gradually increasing with altitude and peaking at ~200 km. The intense Joule heating around 120 km and strong cooling above result in differential heating that produces a sharp TTEIL. However, vertical heat advection broadens the TTEIL and raises the temperature peak from ~120 to ~150 km, causing simulations deviating from observations. Strong local Joule heating also excites traveling atmospheric disturbances that carry the TTEIL signatures to other regions. Our study suggests the importance of including fine‐structure auroral precipitation and subgrid electric field variability in the modeling of storm‐time ionosphere‐thermosphere responses.

    more » « less
  2. Abstract

    We report the first simultaneous, common‐volume lidar observations of thermosphere‐ionosphere Fe (TIFe) and Na (TINa) layers in Antarctica. We also report the observational discovery of nearly one‐to‐one correspondence between TIFe and aurora activity, enhanced ionization layers, and converging electric fields. Distinctive TIFe layers have a peak density of ~384 cm−3and the TIFe mixing ratio peaks around 123 km, ~5 times the mesospheric layer maximum. All evidence shows that Fe+ion‐neutralization is the major formation mechanism of TIFe layers. The TINa mixing ratio often exhibits a broad peak at TIFe altitudes, providing evidence for in situ production via Na+neutralization. However, the tenuous TINa layers persist long beyond TIFe disappearance and reveal gravity wave perturbations, suggesting a dynamic background of neutral Na, but not Fe, above 110 km. The striking differences between distinct TIFe and diffuse TINa suggest differential transport between Fe and Na, possibly due to mass separation.

    more » « less
  3. During geomagnetic storms a large amount of energy is transferred into the ionosphere-thermosphere (IT) system, leading to local and global changes in e.g., the dynamics, composition, and neutral density. The more steady energy from the lower atmosphere into the IT system is in general much smaller than the energy input from the magnetosphere, especially during geomagnetic storms, and therefore details of the lower atmosphere forcing are often neglected in storm time simulations. In this study we compare the neutral density observed by Swarm-C during the moderate geomagnetic storm of 31 January to 3 February 2016 with the Thermosphere-Ionosphere-Electrodynamics-GCM (TIEGCM) finding that the model can capture the observed large scale neutral density variations better in the southern than northern hemisphere. The importance of more realistic lower atmospheric (LB) variations as specified by the Whole Atmosphere Community Climate Model eXtended (WACCM-X) with specified dynamics (SD) is demonstrated by improving especially the northern hemisphere neutral density by up to 15% compared to using climatological LB forcing. Further analysis highlights the importance of the background atmospheric condition in facilitating hemispheric different neutral density changes in response to the LB perturbations. In comparison, employing observationally based field-aligned current (FAC) versus using an empirical model to describe magnetosphere-ionosphere (MI) coupling leads to an 7–20% improved northern hemisphere neutral density. The results highlight the importance of the lower atmospheric variations and high latitude forcing in simulating the absolute large scale neutral density especially the hemispheric differences. However, focusing on the storm time variation with respect to the quiescent time, the lower atmospheric influence is reduced to 1–1.5% improvement with respect to the total observed neutral density. The results provide some guidance on the importance of more realistic upper boundary forcing and lower atmospheric variations when modeling large scale, absolute and relative neutral density variations. 
    more » « less
  4. Abstract We introduce a new numerical model developed to assist with Data Interpretation and Numerical Analysis of ionospheric Missions and Observations (DINAMO). DINAMO derives the ionospheric electrostatic potential at low- and mid-latitudes from a two-dimensional dynamo equation and user-specified inputs for the state of the ionosphere and thermosphere (I–T) system. The potential is used to specify the electric fields and associated F -region E × B plasma drifts. Most of the model was written in Python to facilitate the setup of numerical experiments and to engage students in numerical modeling applied to space sciences. Here, we illustrate applications and results of DINAMO in two different analyses. First, DINAMO is used to assess the ability of widely used I–T climatological models (IRI-2016, NRLMSISE-00, and HWM14), when used as drivers, to produce a realistic representation of the low-latitude electrodynamics. In order to evaluate the results, model E × B drifts are compared with observed climatology of the drifts derived from long-term observations made by the Jicamarca incoherent scatter radar. We found that the climatological I–T models are able to drive many of the features of the plasma drifts including the diurnal, seasonal, altitudinal and solar cycle variability. We also identified discrepancies between modeled and observed drifts under certain conditions. This is, in particular, the case of vertical equatorial plasma drifts during low solar flux conditions, which were attributed to a poor specification of the E -region neutral wind dynamo. DINAMO is then used to quantify the impact of meridional currents on the morphology of F -region zonal plasma drifts. Analytic representations of the equatorial drifts are commonly used to interpret observations. These representations, however, commonly ignore contributions from meridional currents. Using DINAMO we show that that these currents can modify zonal plasma drifts by up to ~ 16 m/s in the bottom-side post-sunset F -region, and up to ~ 10 m/s between 0700 and 1000 LT for altitudes above 500 km. Finally, DINAMO results show the relationship between the pre-reversal enhancement (PRE) of the vertical drifts and the vertical shear in the zonal plasma drifts with implications for equatorial spread F. 
    more » « less
  5. Abstract

    The upper boundary height of the traditional community general circulation model of the ionosphere‐thermosphere system is too low to be applied to the topside ionosphere/thermosphere study. In this study, the National Center for Atmospheric Research Thermosphere‐Ionosphere‐Electrodynamics General Circulation Model (NCAR‐TIEGCM) was successfully extended upward by four scale heights from 400–600 km to 700–1,200 km depending on solar activity, named TIEGCM‐X. The topside ionosphere and thermosphere simulated by TIEGCM‐X agree well with the observations derived from a topside sounder and satellite drag data. In addition, the neutral density, temperature, and electron density simulated by TIEGCM‐X are morphologically consistent with the NCAR‐TIEGCM simulations before extension. The latitude‐altitude distribution of the equatorial ionization anomaly derived from TIEGCM‐X is more reasonable. During geomagnetic storm events, the thermospheric responses of TIEGCM‐X are similar to NCAR‐TIEGCM. However, the ionospheric storm effects in TIEGCM‐X are stronger than those in NCAR‐TIEGCM and are even opposites at some middle and low latitudes due to the presence of more closed magnetic field lines. Defense Meteorological Satellite Program observations prove that the ionospheric storm effect of TIEGCM‐X is more reasonable. The well‐validated TIEGCM‐X has significant potential applications in ionospheric/thermospheric studies, such as the responses to storms, low‐latitude dynamics, and data assimilation.

    more » « less