DOI: 10.5285/8db4c41b-e549-45dd-bc85-386e6e0e6e07
title: Dominant spatial and temporal patterns of horizontal ionospheric plasma velocity variation covering the northern polar region, for the period 1997.0 to 2009.0

description: We present a reanalysis of SuperDARN plasma velocity measurements, using the method of data-interpolating Empirical Orthogonal Functions (EOFs). The northern polar region's radar-measured line of sight Doppler velocities are binned in an equal-area grid (areas of approximately 110,000km2) in quasi-dipole latitude and quasi-dipole magnetic local time (MLT). Within this spatial grid, which extends to 30 degrees colatitude, the plasma velocity is given in terms of cardinal north and east vector components (in the quasi-dipole coordinate frame), with the median of every SuperDARN measurement in the spatial bin taken every 5 minutes. These sparse binned data are infilled to provide a measurement at every spatial and temporal location via EOF analysis, ultimately comprising a series of monthly reanalyses, from 1997.0 to 2009.0. This resource provides a convenient method of using SuperDARN data without its usual extreme sparseness, for studies of ionospheric electrodynamics during solar cycle 23. The reanalyses are provided in monthly sets of orthogonal modes of variability (spatial and temporal patterns), along with the timestamps of each epoch, and the spatial coordinate information of all bin locations. We also provide the temporal mean of the data in each spatial bin, which is removed prior to the EOF analysis. Funding was provided by the NERC grant NE/N01099X/1.
description: The data were gathered using the northern hemisphere radars of the SuperDARN global array, and the fitted Doppler velocities were processed from the original autocorrelation functions using version 4.0 of the radar software toolkit (RSTv4.0) and within that toolkit, fitting routine 'fitacfv2.5'. The method will be described in full in a paper ('A high-resolution model of the ionospheric convection from eigenanalysis of SuperDARN plasma velocities'), presently in prep.
description: See lineage/methodology for SuperDARN data processing programs. Note that the programs used to process this data are works in progress and will be published in the supporting information of the referenced paper.
description: The SuperDARN data were processed to remove ground scatter, and to eliminate measurements with too low power (lower than 3dB), or which had a poor-quality flag (identified in RSTv4.0). When binning the data, range gates below 11 and above 150 (where those values correspond to multiple of 45 km range distance from the radar array location) were not used, since these gave inaccurate locational estimates. Resolution: The bins are of equal area , each 110,000 km2, chosen to maximize the invariant latitudinal resolution while satisfying that there is at least one station contributing to each bin. We present 5 netcdf-formatted datasets, named ElectricFieldModes-ds##.nc, as follows. Data Set ds01. A netcdf-formatted file containing the location information for the two-dimensional spatial bins used in this analysis. Coordinates are in the Quasi-Dipole reference frame. Contains 4 variables: bin_centroids_colatitude, bin_centroids_longitude, bin_limits_colatitude and bin_limits_longitude. The centroids are the locations of the centre of each bin, and the limits of the bins give the region over which the EOF prediction at the centroid is assumed to apply. There are 559 bins in the northern polar region, which is the area of focus for this analysis. They are ordered approximately by latitude, then longitude, but this does not always apply near the 0/360 degree longitude boundary. The temporal dependence of the Quasi Dipole coordinates - required to translate them to other coordinate systems - is supplied by the values in data set Shore-ds02, described below. Data Set ds02. A netcdf-formatted file containing the temporal dependence for each analysis used in this study. The analyses are each one calendar month in length. This netcdf file contains 144 variables, each named 'bin_times_YYYYMM', where YYYY is the year of the analysis, and MM is the month of the analysis. Each of the 144 variables is a set of 5-minute average epochs (the rows are sequentially ordered in time), whose 6 columns are in the format [year, month, day, hour, minute, second]. The 5-minute averages start on the 2nd minute of the hour, encompassing data epochs at 1-minute resolution which start on the zeroth minute and which were averaged in 5-element sets. Data Set ds03. A netcdf-formatted file containing the temporal means of the binned data - these were removed from each monthly binned data set prior to the EOF analysis, and should be added back on for an accurate prediction of the plasma velocity. The file contains two sets of 144 variables, each named 'bin_means_YYYYMM_[component]', where YYYY is the year of the analysis, MM is the month of the analysis, and [component] indicates the cardinal direction component that the values pertain to. The two components are in Quasi-Dipole coordinates, and are either north or east. The units of the values in this file are m/s. Each variable is a vector of 559 rows and 1 column, and the order of the rows is that same as that of the variables in data set Shore-ds01. Data Set ds04. A netcdf-formatted file containing the spatial eigenvectors of the 144 EOF analyses. The file contains 1440 sets of two variables, each named 'eig_s_YYYYMM_modeXX_[component]', where YYYY is the year of the analysis, MM is the month of the analysis, XX is the number of the mode that the eigenvector relates to (where the modes are ranked according to decreasing eigenvalue, with mode 1 corresponding to the largest eigenvalue), and [component] is the same information as given for data set ds03, described above. Each variable has 559 rows and 1 column. The row order is the same as that of the variables in data set Shore-ds01. The units of these data are non-physical, but the product of a pair of spatial and temporal eigenvectors has units of m/s. Data Set ds05. A netcdf-formatted file containing the temporal eigenvectors of the 144 EOF analyses. The file contains 1440 variables, each named 'eig_t_YYYYMM_modeXX', where YYYY is the year of the analysis, MM is the month of the analysis, and XX is the number of the mode that the eigenvector relates to (where the modes are ranked according to decreasing eigenvalue, with mode 1 corresponding to the largest eigenvalue). Each variable has 1 column, and the same number (and order) of rows as the corresponding temporal variable in data set Shore-ds02. The units of these data are non-physical, but the product of a pair of spatial and temporal eigenvectors has units of m/s.