skip to main content

Title: Radar Studies of Height‐Dependent Equatorial F region Vertical and Zonal Plasma Drifts

We present the results of an analysis of long‐term measurements of ionosphericFregionE × Bplasma drifts in the American/Peruvian sector. The analysis used observations made between 1986 and 2017 by the incoherent scatter radar of the Jicamarca Radio Observatory. Unlike previous studies, we analyzed both vertical and zonal components of the plasma drifts to derive the geomagnetically quiet time climatological variation of the drifts as a function of height and local time. We determine the average behavior of the height profiles of the drifts for different seasons and distinct solar flux conditions. Our results show good agreement with previous height‐averaged climatological results of vertical and zonal plasma drifts, despite that they are obtained from different sets of measurements. More importantly, our results quantify average height variations in the drifts. The results show, for example, the solar flux control over the height variation of the vertical drifts. The results also show the weak dependence of the daytime zonal drift profiles on solar and seasonal variations. We quantify the effects of seasonal and solar flux variations on the morphology of the vertical shear in the zonal plasma drifts associated with the evening plasma vortex. Assuming interchangeability between local time and longitude, we tested the curl‐free condition for theFregion electric fields with very good results for all seasons and solar flux conditions. We envision the use of our results to aid numerical modeling of ionospheric electrodynamics and structuring and to assist with the interpretation of satellite observations of low‐latitude plasma drifts.

more » « less
Author(s) / Creator(s):
 ;  ;  ;  
Publisher / Repository:
DOI PREFIX: 10.1029
Date Published:
Journal Name:
Journal of Geophysical Research: Space Physics
Page Range / eLocation ID:
p. 2058-2071
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Previous radar studies have shown that magnitude of the vertical component of equatorial ionosphericE×Bplasma drifts can vary significantly with height, even within mainFregion altitudes. These studies, however, were limited to few observation days. In order to properly quantify the height variation of equatorialFregion vertical drifts, we examined 559 days of measurements made by the incoherent scatter radar of the Jicamarca Radio Observatory between the years of 1986 and 2017. From the observed profiles of vertical plasma drifts, we determined the mean behavior and variability of the height gradients as a function of local time and two distinct solar flux conditions (meanF10.7around 80 and 150 SFU). Only observations made under geomagnetically quiet conditions were considered. Our results quantify the enhanced negative height gradients of vertical drifts near sunset that have been reported in the past. More importantly, we also identify and explain an enhancement in positive gradients near sunrise. We discuss the variability of the height gradients in vertical ionosphericE×Bdrifts at main equatorialFregion heights, and the impact of this variability for satellite observations and studies of ionospheric stability and equatorial spreadF.

    more » « less
  2. 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
  3. We introduce the implementation of a global climatological model of the equatorial ionospheric F-region zonal drifts (EZDrifts) that is made available to the public. The model uses the analytic description of the zonal plasma drifts presented by Haerendel et al. (1992) [ J Geophys Res 97(A2) : 1209–1223] and is driven by climatological models of the ionosphere and thermosphere under a realistic geomagnetic field configuration. EZDrifts is an expansion of the model of the zonal drifts first presented by Shidler & Rodrigues (2021) [ Prog Earth Planet Sci 8 : 26] which was only valid for the Jicamarca longitude sector and two specific solar flux conditions. EZDrifts now uses vertical equatorial plasma drifts from Scherliess & Fejer (1999) [ J Geophys Res 104(A4) : 6829–6842] model which allows it to provide zonal drifts for any day of the year, longitude, and solar flux condition. We show that the model can reproduce the main results of the Shidler & Rodrigues (2021) [ Prog Earth Planet Sci 8 : 26] model for the Peruvian sector. We also illustrate an application of EZDrifts by presenting and discussing longitudinal variabilities produced by the model. We show that the model predicts longitudinal variations in the reversal times of the drifts that are in good agreement with observations made by C/NOFS. EZDrifts also predicts longitudinal variations in the magnitude of the drifts that can be identified in the June solstice observations made by C/NOFS. We also point out data-model differences observed during Equinox and December solstice. Finally, we explain that the longitudinal variations in the zonal plasma drifts are caused by longitudinal variations in the latitude of the magnetic equator and, consequently, in the wind dynamo contributing to the resulting drifts. EZDrifts is distributed to the community through a public repository and can be used in applications requiring an estimate of the overall behavior of the equatorial zonal drifts. 
    more » « less
  4. Abstract

    Numerical experiments are performed using a suite of general circulation models that enable the interaction between a Kelvin wave packet and the ionosphere‐thermosphere (IT) to be elucidated. Focus is on an eastward‐propagating ultra‐fast Kelvin wave (UFKW) packet with periods between 2 and 4 days and zonal wavenumbers=−1 during day of year (DOY) 266–281, 2009. Dissipative processes modify the classic UFKW dynamics (equatorially trapped, small meridional wind component) in three ways: (1) molecular diffusion acts to spread the UFKW zonal (u) and meridional (v) wind fields meridionally, pole to pole, asuandv, respectively, decay and grow with increasing height; (2) due to molecular diffusion, the UFKW spectrum at longer periods and with shorter vertical wavelengths preferentially dissipates with height; and (3) interaction with the diurnally varying IT introduces a westward‐propagatings=+2 component to the wind field that significantly modifies its longitude‐UT structure to include a diurnal modulation. The F‐region ionosphere also responds withs=+2, which originates from the influence of diurnally varying E‐region conductivity onE×Bdrifts. Additional spectral peaks invand ionospheric parameters arise due to longitude variations in the magnetic field. Maximum excursions in NmF2 (as compared with those from a simulation without UFKW forcing) achieve values as large as ±50% but more commonly occur in the range of ±20–30%. The combination of positive and negative responses, and their relative magnitudes, depends on the phasing of the UFKW as it moves zonally relative to the Sun‐synchronous diurnal variation of the ionosphere, in addition to its changing amplitude between DOY 266 and 282. Modifications of order 10 ms−1and −7% to zonal‐mean zonal winds and NmF2, respectively, also result from dissipation of the UFKW packet.

    more » « less
  5. Abstract

    The effect of eastward zonal wind speed (EZWS) on vertical drift velocity (E × Bdrift) that mainly controls the equatorial ionospheric irregularities has been explained theoretically and through numerical models. However, its effect on the seasonal and longitudinal variations ofE × Band the accompanying irregularities has not yet been investigated experimentally due to lack ofF‐layer wind speed measurements. Observations of EZWS from GOCE and ion density andE × Bfrom C/NOFS satellites for years 2011 and 2012 during quite times are used in this study. Monthly and longitudinal variations of the irregularity occurrence,E × B, and EZWS show similar patterns. We find that at most 50.85% of longitudinal variations ofE × Bcan be explained by the longitudinal variability of EZWS only. When the EZWS exceeds 150 m/s, the longitudinal variation of EZWS, geomagnetic field strength, and Pedersen conductivity explain 56.40–69.20% of the longitudinal variation ofE × B. In Atlantic, Africa, and Indian sectors, from 42.63% to 79.80% of the monthly variations of theE × Bcan be explained by the monthly variations of EZWS only. It is found also that EZWS andE × Bmay be linearly correlated during fall equinox and December solstice. The peak occurrence of irregularity in the Atlantic sector during November and December is due to the combined effect of large wind speed, solar terminator‐geomagnetic field alignment, and small geomagnetic field strength and Pedersen conductivity. Moreover, during June solstices, small EZWS corresponds to vertically downwardE × B, which suggests that other factors dominate theE × Bdrift rather than the EZWS during these periods.

    more » « less