First in‐situ measurements of HF radar echoing targets

Abstract

[1] The sounding rocket Investigation of Cusp Irregularities 2 (ICI-2) was launched into the cusp ionosphere over Svalbard to investigate the production of decameter scale irregularities in the electron plasma associated with HF radar backscatter. The main mission objective was to obtain high-resolution measurements of decameter scale electron plasma irregularities and to quantify the growth rate for the gradient drift instability (GDI). At the 5.7 kHz sampling rate of the absolute density measurements, ICI-2 has provided the first documentation in terms of absolute electron density measurements of how 10-m structures are located on km scale electron density gradients. ICI-2 traversed a cusp electron density structure created by ongoing soft precipitation. 10-m scale irregularities were generated at km scale density gradients. The estimated growth time for the GDI process was 10-50 seconds. Citation:

GPS scintillation effects associated with polar cap patches and substorm auroral activity: direct comparison

“…Obviously, there may be velocity shears associated with auroral arcs that can rapidly develop small scale irregularities on large scale structures (auroral blobs) by the KelvinHelmholtz type, velocity shear Instability (KHI) (Kersley et al 1988;Keskinen et al 1988;Carlson et al 2008;Carlson 2012). The auroral precipitation interacting with the polar cap patches may give rise to plasma gradients on which the GDI can operate as has been documented in the dayside cusp (Moen et al 2012). Apparently from our observations, the auroral blobs can stand out as the most violent scintillation region from the GPS user's point of view.…”

“…During their convection in the polar cap, the Gradient Drift Instability (GDI) acts on them and develops small scale irregularities on the trailing edge. On the leading edge, the plasma density gradient sets up polarization fields that stabilize the plasma structure (Keskinen & Ossakow 1983), as observed by Moen et al (2012). However, although the GDI occurs initially on the trailing edge, the nonlinear development could penetrate through the entire patch (Gondarenko & Guzdar 2004).…”

Overview of the 2015 St. Patrick’s day storm and its consequences for RTK and PPP positioning in Norway

“…In the case study by van der Meeren et al (2015), scintillations were not observed for patches outside of the region of auroral emissions/particle precipitation, but strong scintilllation was observed in association with patches co-located with strong auroral emissions/particle precipitation. In-situ observations of patches by Moen et al (2012) indicate that particle precipitation is a driver of plasma instabilities that form structures on scales that cause scintillation in GNSS signals. Figure 5 shows a zoomed-in view for 12:00 to 17:00 UT on the 17th, the time period that had a strong eastward current.…”

“…Weber et al 1986;Krankowski et al 2006;Kintner et al 2007;Tiwari et al 2010;Moen et al 2012;Prikryl et al 2013;Jin et al 2014). They are either transported across the polar cap from the dense ionospheric plasma at the sunlit side of the Earth or created by particle precipitation in the cusp.…”

A modeling study of asymmetries in plasma irregularity characteristics near gradient reversals

“…Observations of large-scale density structures in the polar cap ionosphere such as polar patches and Sun-aligned arcs have shown some asymmetry in the small-scale irregularity characteristics between their leading and trailing edges (e.g., Weber et al, 1984). In general, trailing edges exhibit stronger structuring, which is often interpreted in terms of more favorable conditions for the gradientdrift instability (GDI) along the trailing edge (Weber et al, 1984;Milan et al, 2002;Koustov et al, 2012;Moen et al, 2012).…”