M. A. McCready

Multiradar observations of the polar tongue of ionization

[1] We present a global view of large-scale ionospheric disturbances during the main phase of a major geomagnetic storm. We find that the low-latitude, auroral, and polar latitude regions are coupled by processes that redistribute thermal plasma throughout the system. For the large geomagnetic storm on 20 November 2003, we examine data from the high-latitude incoherent scatter radars at Millstone Hill, Sondrestrom, and EISCAT Tromso, with SuperDARN HF radar observations of the high-latitude convection pattern and DMSP observations of in situ plasma parameters in the topside ionosphere. We combine these with north polar maps of stormtime plumes of enhanced total electron content (TEC) derived from a network of GPS receivers. The polar tongue of ionization (TOI) is seen to be a continuous stream of dense cold plasma entrained in the global convection pattern. The dayside source of the TOI is the plume of storm enhanced density (SED) transported from low latitudes in the postnoon sector by the subauroral disturbance electric field. Convection carries this material through the dayside cusp and across the polar cap to the nightside where the auroral F region is significantly enhanced by the SED material. The three incoherent scatter radars provided full altitude profiles of plasma density, temperatures, and vertical velocity as the TOI plume crossed their different positions, under the cusp, in the center of the polar cap, and at the midnight oval/polar cap boundary. Greatly elevated F peak density (>1.5E12 m 3 ) and low electron and ion temperatures (2500 K at the F peak altitude) characterize the SED/TOI plasma observed at all points along its high-latitude trajectory. For this event, SED/TOI F region TEC (150–1000 km) was 50 TECu both in the cusp and in the center of the polar cap. Large, upward directed fluxes of O+ (>1.E14 m 2 s 1 ) were observed in the topside ionosphere

Ionospheric local model and climatology from long-term databases of multiple incoherent scatter radars

Empirical ionospheric local models have been developed from long-term data sets of seven incoherent scatter radars spanning invariant latitudes from 25 to 75 in American, European and Asian longitudes at Svalbard, Tromso, Sondrestrom, Millstone Hill, St. Santin, Arecibo and Shigaraki. These models, as important complements to global models, represent electron density, ion and electron temperatures, and ion drifts in the E and F regions, giving a comprehensive quantitative description of ionospheric properties. A case study of annual ionospheric variations in electron density and ion temperature is presented based on some of these models. Clear latitudinal, longitudinal, and altitude dependency of annual and semiannual components are found.

Ionospheric structure and the generation of auroral roar

Ionospheric electron density data from the Sondrestrom incoherent scatter radar (ISR) have been used to characterize the structure of the F region ionosphere during ground-based LF/MF/HF receiver observations of natural ionospheric radio emissions known as auroral roar. In five out of six cases, the F region ionosphere has significant horizontal Ne gradient scale lengths ( , measured with 23–137 km spatial resolution). In three of these cases, localized F region auroral ionospheric cavities, with horizontal scales ∼50 km, are observed. In one of six cases, the ionosphere lacks either of these features, and a laminar, mostly unstructured, F region is observed. The data suggest that auroral roar events may occur for a range of large-scale (>30 km) ionospheric conditions. Some theories for the generation of auroral roar require that the relationship between the electron plasma frequency (ƒpe) and the electron gyrofrequency (ƒce) in the source region is , where n is the harmonic number of the observed emission. Comparisons between observed auroral roar emission frequencies, ISR observations of electron density, and the IGRF model for the magnetic field show that this frequency-matching condition holds somewhere in the ionosphere in 16 out of 18 cases studied and in all 3 cases of ISR elevation scans capable of measuring a source located directly overhead.

Ionospheric ion temperature climate and upper atmospheric long-term cooling†

It is now recognized that Earths upper atmosphere is experiencing a long-term cooling over the past several solar cycles. The potential impact of the cooling on societal activities is significant, but a fundamental scientific question exists regarding the drivers of the cooling. New observations and analyses provide crucial advances in our knowledge of these important processes. We investigate ionospheric ion temperature climatology and long-term trends using up-to-date large and consistent ground based datasets as measured by multiple incoherent scatter radars (ISRs). The very comprehensive view provided by these unique observations of the upper atmospheric thermal status allows us to address drivers of strong cooling previously observed by ISRs. We use observations from two high latitude sites at Sondrestrom (Invariant latitude 73.2°N) from 1990-2015, and Chatanika/Poker Flat (Invariant latitude 65.9°N) over the span of 1976-2015 (with a gap from 1983-2006). Results are compared to conditions at the mid-latitude Millstone Hill site (Invariant latitude 52.8°N) from 1968-2015. The aggregate radar observations have very comparable and consistent altitude dependence of long-term trends. In particular, the lower F region (< 275 km) exhibits dayside cooling trends that are significantly higher (-3 to -1K/year at 250 km) than anticipated from model predictions given the anthropogenic increase of greenhouse gases. Above 275 km, cooling trends continue to increase in magnitude but values are strongly dependent on magnetic latitude, suggesting the presence of significant downward influences from non-neutral atmospheric processes.

Ionospheric Challenges of the International Polar Year

Fifty years ago, the first International Geophysical Year (IGY) generated a huge step function increase in observations of ionospheric variability associated with the almost continuous geomagnetic activity experienced during the largest solar maximum of the past 100 years. In turn, these observations fueled more than a decade of theoretical advancement of magnetospheric-ionospheric electrodynamics and geomagnetic storm physics. In stark contrast, the current International Polar Year (IPY; 2007–2009) is occurring during what may well turn out to be the deepest solar minimum in 100 years. Potentially, it could be a very geomagnetically quiet period, a period during which ionospheric variability will be driven by processes in the troposphere and mesosphere. Since the variability of the ionosphere-thermosphere system associated with the upward propagating planetary, tidal, and gravity waves from the lower atmosphere is expected to be independent of the solar cycle, the IPY period is an ideal time to study the interchanges between the lower and upper atmospheric regions.