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

Abstract

We introduce an algorithm to detect polar-cap patches in an Advanced Modular Incoherent Scatter Radar data set, using the Resolute Bay Incoherent Scatter Radar-North. Patches are detected by comparing plasma density (n e ) measurements along each radar beam to a 30-min running average of the median n e within the field-of-view. The algorithm is tested and shown to be an effective tool for polar-cap patch studies. It is then used to conduct a survey of patches over Resolute Bay for two separate periods of time centered on March and December of 2010. The survey shows that polar-cap patches are almost always present in both sunlit and nighttime conditions. However, the population is subdued during the day. The patch densities are found to vary by as much as an order of magnitude throughout the day. Their ion temperature is relatively constant, only varying by 100 K between the sunlit and nighttime conditions. By contrast, their electron temperature is very sensitive to the solar zenith angle and changes dramatically around sunrise. Plain Language SummaryWe introduce an algorithm to detect polar-cap patches in a radar data set. Patches are large-scale F region plasma density enhancements, positive plasma density perturbations above the background plasma density, and are typically observed at high latitudes. The patches are detected by comparing plasma density measurements at different points within the radar's field-of-view to a 30-min running average of the median plasma density within the field-of-view. The algorithm is tested and validated and used to analyze data collected by the Resolute Bay Incoherent Scatter Radar-North over several days in March and December 2010. Our analysis reveals that the density of detected patches varies by as much as an order of magnitude throughout the day, and their electron temperature is very sensitive to whether or not the patch is sunlit and changes dramatically around sunrise.

Statistical Characteristics of Polar Cap Patches Observed by RISR‐C

“…In general, the ion temperatures increase slowly around 1000 K as altitude increases, which are ~200 K higher than Perry and St.‐Maurice (, Figure 4.17) reported based on data taken in 2010 near deep solar minimum. Thus, the difference is likely due to the solar cycle effect.…”

“…In the midnight sector, electron temperature within the patches does not show large difference with the sector median. The results by Perry and St.‐Maurice (, Figure 4.18) also showed patch electron temperature ~1800–2000 K in sunlit region and ~1000 K in dark region. In the dawn and dusk sectors, electron temperature within the patches is slightly lower than the sector median values, but the differences are smaller comparing with that in the noon sector.…”

“…Fortunately, the newly deployed Resolute Bay Incoherent Radar (RISR) provides such a capability. Perry and St.-Maurice (2018) used a patch detection algorithm on the northern face of the RISR (RISR-N) data measured during 5 days each in March and December in 2010, and reported distributions of F-region plasma density and temperatures of the patches, but the statistical profiles within the patches were not studied. In our work, based on 7-month measurements taken by the Canadian component of the RISR radars (RISR-C; Gillies et al, 2016) in 2016, we developed an automatic algorithm to identify the polar cap patches and constructed a database of 437 patches.…”

Observations and modeling of scintillation in the vicinity of a polar cap patch

“…6). This event was chosen because it was a relatively clear and isolated density enhancement that abides by most traditional definitions of polar cap patches (a plasma density enhancement at least twice the background density) (Weber et al, 1984;Perry & St.-Maurice, 2018;Ren et al, 2018). Furthermore, it occurred when both RISR-N and RISR-C were operating in an imaging mode in conjunction with several independent scintillation observations.…”

Resolving the High‐Latitude Ionospheric Irregularity Spectra Using Multi‐Point Incoherent Scatter Radar Measurements

“…The high‐latitude ionosphere is dynamic and replete with a variety of plasma density irregularities. Enhancements in plasma density, such as polar cap patches (Crowley, 1996), can form in a number of ways, such as from the transportation and mixing of dense plasma (like extreme ultraviolet photoionized plasma) with relatively depleted plasma (Zhang et al., 2013), or from particle impact ionization (e.g., Goodwin et al., 2015; MacDougall & Jayachandran, 2007; Oksavik et al., 2006; Perry & Maurice, 2018; Walker et al., 1999; Weber et al., 1984). Plasma density depletions, such as polar holes, can also result through transportation (Forsythe et al., 2021; Sojka et al., 1981a, 1981b), but also result through enhanced plasma recombination (Perry et al., 2015; Zettergren & Semeter, 2012).…”