Magnetic-local-time dependency of radiation belt electron precipitation: impact on ozone in the polar middle atmosphere

<div> <div> <div> <p>The radiation belts are regions in the near-Earth space where solar wind electrons are captured by the Earth’s magnetic field. A portion of these electrons is continuously lost into the atmosphere where they cause ionization and chemical changes. Driven by the solar activity, the electron forcing leads to ozone variability in the polar stratosphere and mesosphere. Understanding the possible dynamical connections to regional climate is an ongoing research activity which supports the assessment of greenhouse-gas-driven climate change by a better definition of the solar-driven variability. In the context of the Coupled Model Intercomparison Project Phase 6 (CMIP6), energetic electron and proton precipitation is included in the solar-forcing recommendation for the first time. For the radiation belt electrons, the CMIP6 forcing is from a daily zonal-mean proxy model. This zonal-mean model ignores the well-known dependency of precipitation on magnetic local time (MLT), i.e. its diurnal variability. Here we use the Whole Atmosphere Community Climate Model with its lower-ionospheric-chemistry extension (WACCM-D) to study effects of the MLT dependency of electron forcing on the polar-ozone response. We analyse simulations applying MLT-dependent and MLT-independent forcings and contrast the resulting ozone responses in monthly-mean data as well as in monthly means at individual local times. We consider two cases: (1) the year 2003 and (2) an extreme, continuous forcing. Our results indicate that the ozone responses to the MLT-dependent and the MLT-independent forcings are very similar, and the differences found are small compared to those caused by the overall uncertainties related to the representation of electron forcing in climate simulations. We conclude that the use of daily zonal-mean electron forcing will provide an accurate ozone response in long-term climate simulations.</p> </div> </div> </div>

Geomagnetically induced currents during the 07–08 September 2017 disturbed period: a global perspective

Measurements from six longitudinally separated magnetic observatories, all located close to the 53° mid-latitude contour, are analysed. We focus on the large geomagnetic disturbance that occurred during 7 and 8 September 2017. Combined with available geomagnetically induced current (GIC) data from two substations, each located near to a magnetic observatory, we investigate the magnetospheric drivers of the largest events. We analyse solar wind parameters combined with auroral electrojet indices to investigate the driving mechanisms. Six magnetic field disturbance events were observed at mid-latitudes with dH/dt > 60 nT/min. Co-located GIC measurements identified transformer currents >15 A during three of the events. The initial event was caused by a solar wind pressure pulse causing largest effects on the dayside, consistent with the rapid compression of the dayside geomagnetic field. Four of the events were caused by substorms. Variations in the Magnetic Local Time of the maximum effect of each substorm-driven event were apparent, with magnetic midnight, morning-side, and dusk-side events all occurring. The six events occurred over a period of almost 24 h, during which the solar wind remained elevated at >700 km s−1, indicating an extended time scale for potential GIC problems in electrical power networks following a sudden storm commencement. This work demonstrates the challenge of understanding the causes of ground-level magnetic field changes (and hence GIC magnitudes) for the global power industry. It also demonstrates the importance of magnetic local time and differing inner magnetospheric processes when considering the global hazard posed by GIC to power grids.

Magnetic-local-time dependency of radiation belt electron precipitation: impact on ozone in the polar middle atmosphere

The radiation belts are regions in the near-Earth space where solar wind electrons are captured by the Earth's magnetic field. A portion of these electrons is continuously lost into the atmosphere where they cause ionization and chemical changes. Driven by the solar activity, the electron forcing leads to ozone variability in the polar stratosphere and mesosphere. Understanding the possible dynamical connections to regional climate is an ongoing research activity which supports the assessment of greenhouse-gas-driven climate change by a better definition of the solar-driven variability. In the context of the Coupled Model Intercomparison Project Phase 6 (CMIP6), energetic electron and proton precipitation is included in the solar-forcing recommendation for the first time. For the radiation belt electrons, the CMIP6 forcing is from a daily zonal-mean proxy model. This zonal-mean model ignores the well-known dependency of precipitation on magnetic local time (MLT), i.e. its diurnal variability. Here we use the Whole Atmosphere Community Climate Model with its lower-ionospheric-chemistry extension (WACCM-D) to study effects of the MLT dependency of electron forcing on the polar-ozone response. We analyse simulations applying MLT-dependent and MLT-independent forcings and contrast the resulting ozone responses in monthly-mean data as well as in monthly means at individual local times. We consider two cases: (1) the year 2003 and (2) an extreme, continuous forcing. Our results indicate that the ozone responses to the MLT-dependent and the MLT-independent forcings are very similar, and the differences found are small compared to those caused by the overall uncertainties related to the representation of electron forcing in climate simulations. We conclude that the use of daily zonal-mean electron forcing will provide an accurate ozone response in long-term climate simulations.

Magnetic local time dependency of radiation belt electron precipitation: impact on polar ozone

The radiation belts are regions in the near-Earth space where solar wind electrons are captured by the Earth's magnetic field. A portion of these electrons is continuously lost into the atmosphere where they cause ionisation and chemical changes. Driven by solar activity, electron forcing leads to ozone variability in the polar regions. Understanding possible dynamical connections to regional climate is an on-going research activity which supports the assessment of greenhouse gas driven climate change by better definition of the solar-driven variability. In the context of the Coupled Model Intercomparison Project Phase 6 (CMIP6), energetic electron and proton precipitation is included in the solar forcing recommendation for the first time. For radiation belt electrons, CMIP6 forcing is from a daily, zonal mean proxy model. This zonal mean model ignores the well-known dependency of precipitation on magnetic local time (MLT), i.e. its diurnal variability. Here we use the Whole Atmosphere Community Climate Model with lower ionospheric chemistry extension (WACCM-D) to study the effect of MLT dependency of electron forcing on the polar ozone response. We analyse simulations applying MLT-dependent and MLT-independent forcings, and contrast ozone responses in monthly mean data as well as in monthly means of individual local time sectors. We consider two cases: 1) year 2003 and 2) extreme, long-duration forcing. Our results indicate that the ozone responses to MLT-dependent and MLT-independent forcings are very similar, and the differences found are small compared to those related to overall uncertainties in electron forcing. We conclude that electron forcing that ignores the MLT dependency will still provide an accurate ozone response in long-term climate simulations.

Mid-altitude cusp dynamics and properties during the IMF By dominated intervals

<p>Observations inside the cusp can be used as distant monitoring of the large-scale geometry and properties of the magnetic reconnection at the magnetopause. The recent modelling and observations of the cusp and flux transfer events in the vicinity of the magnetopause show that the reconnection can occur along the X-line extended over many hours of magnetic local time (MLT), comprising sites of both component and anti-parallel reconnection scenarios. Such observations are in contradiction to the statistical DMSP studies showing that the cusp is rather limited in magnetic local time with an average size 2.5 hours of MLT. Moreover, some past observations indicate that the cusp is moving in response to the changes of the IMF By component, suggesting that the cusp is formed due to anti-parallel reconnection along the X-line limited in MLT.</p><p>In this presentation we analyse several events of the mid-altitude cusp observations during the Cluster campaign when the satellites cross the cusp mainly along the longitude in a string-of-pearls configuration during an Interplanetary Magnetic Field (IMF) configuration with a stable and dominant IMF By-component. During this particular Cluster orbit it was possible to define the dawn and dusk cusp boundaries and to study plasma parameters inside different parts of the cusp region. The observations will be discussed in terms of the cusp extension, cusp motion, and possible formation of the ‘double’ cusp structures. Finally, we will consider what these observations reveal about the large-scale reconnection geometry at the magnetopause.</p>

Surveying pulsating auroras

The early-morning auroral oval is dominated by pulsating auroras. These auroras have often been discussed as if they are one phenomenon, but they are not. Pulsating auroras are separable based on the extent of their pulsation and structuring into at least three subcategories. This study surveyed 10 years of all-sky camera data to determine the occurrence probability for each type of pulsating aurora in magnetic local time and magnetic latitude. Amorphous pulsating aurora (APAs) are a pervasive, nearly daily feature in the early-morning auroral oval which have an 86 % chance of occurrence at their peak. Patchy pulsating auroras (PPAs) and patchy auroras (PAs) are less common, peaking at 21 % and 29 %, respectively. Before local midnight, pulsating auroras are almost exclusively APAs. Occurrence distributions of APAs, PPAs, and PAs are mapped into the equatorial plane to approximately locate their source regions. The PA and PPA distributions primarily map to locations approximately between 4 and 9 RE, while some APAs map to farther distances, suggesting that the mechanism which structures PPAs and PAs is constrained to the inner magnetosphere. This is in agreement with Grono and Donovan (2019), which located these auroras relative to the proton aurora.

Magnetic local time asymmetries in precipitating electron and proton populations with and without substorm activity

The magnetic local time (MLT) dependence of electron (0.15–300 keV) and proton (0.15–6900 keV) precipitation into the atmosphere based on National Oceanic and Atmospheric Administration POES and METOP satellite data during 2001–2008 was described. Using modified APEX coordinates the influence of particle energy, substorm activity and geomagnetic disturbance on the MLT flux distribution was statistically analysed. Some of the findings are the following. a. Substorms mostly increase particle precipitation in the night sector by about factor 2–4, but can also reduce it in the day sector.b. MLT dependence can be assigned to particles entering the magnetosphere at the cusp region and magnetospheric particles in combination with energy-specific drifts (in agreement with Newell et al., 2009).c. MLT flux differences of up to 2 orders of magnitude have been identified inside the auroral oval during geomagnetically disturbed conditions. The novelty here is the comprehensive coverage of energy bands and the focus on asymmetry.d. The maximum flux asymmetry ratio depends on particle energy, decreasing with Kp for low energetic particles and increasing with Kp for higher energy electrons, while high energy protons show a more complex dependency. While some aspects may already have been known, the quantification of the flux asymmetry sheds new light on MLT variation.