Automated identification and tracking of polar-cap plasma patches at solar minimum

Abstract

Abstract.A method of automatically identifying and tracking polar-cap plasma patches, utilising data inversion and feature-tracking methods, is presented. A well-established and widely used 4-D ionospheric imaging algorithm, the Multi-Instrument Data Assimilation System (MIDAS), inverts slant total electron content (TEC) data from groundbased Global Navigation Satellite System (GNSS) receivers to produce images of the free electron distribution in the polar-cap ionosphere. These are integrated to form vertical TEC maps. A flexible feature-tracking algorithm, TRACK, previously used extensively in meteorological storm-tracking studies is used to identify and track maxima in the resulting 2-D data fields. Various criteria are used to discriminate between genuine patches and "false-positive" maxima such as the continuously moving day-side maximum, which results from the Earth's rotation rather than plasma motion. Results for a 12-month period at solar minimum, when extensive validation data are available, are presented. The method identifies 71 separate structures consistent with patch motion during this time. The limitations of solar minimum and the consequent small number of patches make climatological inferences difficult, but the feasibility of the method for patches larger than approximately 500 km in scale is demonstrated and a larger study incorporating other parts of the solar cycle is warranted. Possible further optimisation of discrimination criteria, particularly regarding the definition of a patch in terms of its plasma concentration enhancement over the surrounding background, may improve results.

Resolute Bay Incoherent Scatter Radar observations of plasma structures in the vicinity of polar holes

“…Investigations of density depressions can be regarded as a complementary effort to studies of production and evolution of plasma enhancements such as polar patches [Crowley et al, 1993]. In this sense, the current study complements well the recent experimental studies of polar patches that were enabled by expanding capabilities to image the polar cap using radio and optical techniques [e.g., Hosokawa et al, 2009Hosokawa et al, , 2014Oksavik et al, 2010;Dahlgren et al, 2012b;Moen et al, 2013;Zhang et al, 2013;Burston et al, 2014;Nishimura et al, 2014]. Moreover, the current study also focused on series of propagating density enhancements in the vicinity of density depressions and can therefore be regarded as complementary to both of these broader efforts.…”

“…Automatic structure identification, tracking, and inferring velocities from series of 2-D images has an advantage of producing true 2-D velocities for most structure shapes. However, this is a nontrivial image analysis problem, with existing solutions limited to a particular imaging system and a particular set of conditions [Makarevitch et al, 2004;Hosokawa et al, 2009;Burston et al, 2014]. In most studies that consider structure velocity, a simpler process is employed in which 1-D or 2-D velocities are inferred from the slope(s) of the linear fit to the consecutive positions of the measured parameter such as density or radar power [e.g., Bahcivan et al, 2010;Oksavik et al, 2010].…”

“…A useful extension of the current analysis would be the development of an automatic algorithm for structure tracking and velocity estimates using ISR data. As discussed in sections 1 and 3.4, this presents numerous challenges including the need to apply corrections if measurements in EW-aligned and NS-aligned sampling areas are considered or the need to appropriately characterize individual structures if 2-D images are used [e.g., Makarevitch et al, 2004;Dahlgren et al, 2012a;Burston et al, 2014].…”

“…Localized enhancements in plasma density (100-1000 km in extent) known as polar patches have received even more attention than their low-density counterparts [Buchau et al, 1983;Weber et al, 1984;Rodger et al, 1994;Milan et al, 2002;Hosokawa et al, 2009;Dahlgren et al, 2012aDahlgren et al, , 2012bZhang et al, 2013;Burston et al, 2014;Goodwin et al, 2015]. A fundamental problem is what causes the plasma to be chopped into islands and what happens with patches after they have been separated from their source region including further structuring processes [Carlson, 2012].…”

A Polar‐Cap Patch Detection Algorithm for the Advanced Modular Incoherent Scatter Radar System

“…Nevertheless, their algorithm detected over 20,000 patches (10,000 for each satellite) over a period spanning December 2013 to August 2016. Separate, alternative methods for patch detection were introduced by Noja et al (2013) and Burston et al (2014), who reported on data sets containing several thousand and 71 patches, respectively. In both cases, patches were identified through a satellite-based total electron content (TEC) measurement.…”