Technical Article

Low latitude monthly total electron content composite correlations

¹ Remote Sensing Division, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC, 20375, USA
² Space Science Division, Naval Research Laboratory, 4555 Overlook Avenue SW, Washington, DC, 20375, USA

^* Corresponding author: douglas.allen@nrl.navy.mil

Received: 15 July 2022
Accepted: 24 February 2023

Abstract

Spatial correlations of total electron content (TEC) variability are compared among two SAMI3 model runs and Jet Propulsion Laboratory Global Ionospheric Maps (JPL/GIM). Individual monthly correlation maps are constructed with Equatorial reference points at 12 evenly spaced longitudes and 12 universal times. TEC composite correlations (TCCs) are then calculated by averaging the individual maps, shifted zonally to synchronize local time. The TCC structures are quantified using Gaussian fits in the zonal and meridional directions. A non-zero large-scale “base correlation” is found in all three datasets for 2014, a year with high solar activity. Higher base correlations generally occur in the SAMI3 runs than in JPL/GIM. The SAMI3 run driven with climatological neutral fields shows higher correlations than the run driven with neutrals from a Whole Atmosphere Community Climate Model with thermosphere–ionosphere eXtension (WACCM-X) simulation. Base correlation values strongly correlate with monthly F10.7 standard deviations. Empirical orthogonal function (EOF) analyses confirm that large-scale correlations are usually, although not always, related to solar forcing. Strong correlations between the Ap index and EOF modes are also observed, consistent with the geomagnetic forcing of the TEC field. The widths of the correlation structures are also examined, and these vary considerably with local time, month, and dataset. Off-Equator conjugate point correlations are also calculated from each dataset and variations with the month and local time are analyzed. Analysis of TCCs for 2010, a year with low solar activity, shows that base correlations as well as correlations of the first EOF mode with F10.7 are generally weaker than in 2014.