A. G. Burrell

Automatically determining the origin direction and propagation mode of high‐frequency radar backscatter

Elevation angles of returned backscatter are calculated at Super Dual Auroral Radar Network radars using interferometric techniques. These elevation angles allow the altitude of the reflection point to be estimated, an essential piece of information for many ionospheric studies. The elevation angle calculation requires knowledge of the azimuthal return angle. This directional angle is usually assumed to lie along a narrow beam from the front of the radar, even though the signals are known to return from both in front of and behind the radar. If the wrong direction of return is assumed, large uncertainties will be introduced through the azimuthal return angle. This paper introduces a means of automatically determining the correct direction of arrival and the propagation mode of backscatter. The application of this method will improve the accuracy of backscatter elevation angle data and aid in the interpretation of both ionospheric and ground backscatter observations.

PYSAT: Python Satellite Data Analysis Toolkit: PYSAT

R. A. Stoneback, W. B. Hanson Center for Space Sciences, 800 W. Campbell Rd. WT 15, Richardson, TX 75080, USA. (rstoneba@utdallas.edu) A. G. Burrell, W. B. Hanson Center for Space Sciences, 800 W. Campbell Rd. WT 15, Richardson, TX 75080, USA. J. Klenzing, Space Weather Lab / Code 674, Goddard Space Flight Center, Greenbelt, MD, USA M. D. Depew, W. B. Hanson Center for Space Sciences, 800 W. Campbell Rd. WT 15, Richardson, TX 75080, USA.

Seasonal and temporal variations of field-aligned currents and ground magnetic deflections during substorms

Field-aligned currents (FACs), also known as Birkeland currents, are the agents by which energy and momentum are transferred to the ionosphere from the magnetosphere and solar wind. This coupling is enhanced at substorm onset through the formation of the substorm current wedge. Using FAC data from the Active Magnetosphere and Planetary Electrodynamics Response Experiment and substorm expansion phase onsets identified using the Substorm Onsets and Phases from Indices of the Electrojet technique, we examine the Northern Hemisphere FACs in all local time sectors with respect to substorm onset and subdivided by season. Our results show that while there is a strong seasonal dependence on the underlying FACs, the increase in FACs following substorm onset only varies by 10% with season, with substorms increasing the hemispheric FACs by 420 kA on average. Over an hour prior to substorm onset, the dayside currents in the postnoon quadrant increase linearly, whereas the nightside currents show a linear increase starting 20-30 min before onset. After onset, the nightside Region 1, Region 2, and nonlocally closed currents and the SuperMAG AL (SML) index follow the Weimer (1994, https://doi.org/10.1029/93JA02721) model with the same time constants in each season. These results contrast earlier contradictory studies that indicate that substorms are either longer in the summer or decay faster in the summer. Our results imply that, on average, substorm FACs do not change with season but that their relative impact on the coupled magnetosphere-ionosphere system does due to the changes in the underlying currents.

e‐POP RRI provides new opportunities for space‐based, high‐frequency radio science experiments

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Phase calibration of interferometer arrays at high-frequency radars: INTERFEROMETER PHASE CALIBRATION

Elevation angles of backscattered signals are calculated at the Super Dual Auroral Radar Network (SuperDARN) high-frequency radars using interferometric techniques. These elevation angles make it possible to estimate the geographic location of the scattering point, an essential piece of information for many ionospheric studies. One of the most difficult parameters to measure is the effective time delay caused by the difference in the electrical path length that connects the main array and the interferometer arrays to the correlator (δtc). This time delay causes a bias in the measured difference in the signal phase, also known as a phase bias. Phase calibration is difficult due to unknown physical attributes of the hardware and the remote location of many radars. This leads to the possibility of sudden external changes, slow temporal drift, and a dependence on transmission frequency. However, it is possible to estimate δtc using the radar observations themselves. This article presents a method for estimating δtc using backscatter with a known location, such as backscatter from artificially generated irregularities, meteor echoes, or distinct groundscatter, which incorporates the uncertainty in the observations and may be used autonomously. Applying the estimated δtc is shown to improve elevation angle uncertainties at one of the SuperDARN radars from their current potential tens of degrees to less than a degree.

The changing polar ionosphere: A comparative climatology of solar cycles 23 and 24

The polar ionosphere is a dynamic region that readily responds to changes in solar irradiance, the solar wind, the magnetosphere, and the neutral atmosphere. The most recent solar minimum brought to light gaps in the current understanding of the relationship between ionospheric structure and solar irradiance. The Super Dual Auroral Radar Network (SuperDARN), a High Frequency (HF) over-the-horizon radar network that provides continuous coverage of the northern and southern poles, offers an invaluable dataset for studying long-term ionospheric variability. SuperDARN has been providing extensive coverage of the polar ionosphere in both hemispheres since 1995 (the solar minimum preceding the 23rd solar cycle).