Energetic Electron Precipitation Events Research Articles

Estimation of Energy Spectrum of Precipitating Magnetospheric Electrons Based on Bremsstrahlung X‐Ray Fluxes Recorded in the Atmosphere

AbstractNumerous energetic electron precipitation events were recorded since 1963 in the atmosphere at polar latitudes in the course of regular measurements of charged particle fluxes in the Earth's atmosphere being performed by the Lebedev Physical Institute. The experimental data obtained represent the only uniform database in the world on electron precipitation events recorded directly in the atmosphere well below satellite orbits. The precipitating electrons are absorbed in the upper atmosphere. However, they generate X‐rays that can penetrate deep into the atmosphere sometimes down to altitudes of 20–35 km accessible to balloon measurements. These experimental data allow studying energy, temporal and spatial characteristics of electron precipitation events. In particular, based on PLANETOCOSMICS/GEANT4 we developed a method for evaluating the energy spectra of the primary flux of precipitating electrons. This method was used for evaluation of primary spectra of precipitating electrons assuming exponential energy distribution of incident electrons. Now, for the development of the method, we present the possibility of determining the energy spectra of electrons in the power‐law form, using new software RUSCOSMICS code. This new method, based on the GEANT4 software, makes it possible to describe the transport of precipitating electrons in the atmosphere taking into account the evolution of the energy and pitch‐angle distributions of electrons and X‐ray photons.

Mesospheric ionization during substorm growth phase

Many studies have been conducted about the impact of energetic charged particles on the atmosphere during geomagnetically active times, while quiet time effects are poorly understood. We identified two energetic electron precipitation (EEP) events during the growth phase of moderate substorms and estimated the mesospheric ionization rate for an EEP event for which the most comprehensive dataset from ground-based and space-born instruments was available. The mesospheric ionization signature reached below 70 km altitude and continued for ~15 min until the substorm onset, as observed by the PANSY radar and imaging riometer at Syowa Station in the Antarctic region. We also used energetic electron flux observed by the Arase and POES 15 satellites as the input for the air-shower simulation code PHITS to quantitatively estimate the mesospheric ionization rate. The calculated ionization level due to the precipitating electrons is consistent with the observed value of cosmic noise absorption. The possible spatial extent of EEP is estimated to be ~8 h MLT in longitude and ~1.5° in latitude from a global magnetohydrodynamic simulation REPPU and the precipitating electron observations by the POES satellite, respectively. Such a significant duration and spatial extent of EEP events suggest a non-negligible contribution of the growth phase EEP to the mesospheric ionization. Combining the cutting-edge observations and simulations, we shed new light on the space weather impact of the EEP events during geomagnetically quiet times, which is important to understand the possible link between the space environment and climate.

Stratospheric X‐Rays Detected at Midlatitudes With a Miniaturized Balloon‐Borne Microscintillator‐PiN Diode System

AbstractA miniaturized scintillator (“microscintillator”), was flown on a meteorological radiosonde to observe energetic particles in the lower atmosphere. A PiN diode was used to measure the light from the microscintillator to count rates and energies of ionizing radiation from the ground up to the stratosphere (32 km). The flight, over the southern UK on August 27, 2018, occurred during a geomagnetic storm. Low‐energy (50–150 keV) particles in the stratosphere were detected in addition to the usual signal from higher‐energy cosmic rays. Unusually for these miniaturized radiosonde systems, which are designed to be disposable, the payload was retrieved. This allowed for re‐calibration of the microscintillator, which confirmed the low‐energy particle detection. Laboratory tests excluded thermal effects on the microscintillator instrument as the origin of the signal. Data from the NOAA POES spacecraft offer the explanation that the microscintillator detected bremstrahhlung X‐rays from energetic electron precipitation (EEP). EEP events may affect weather and climate through a range of physical mechanisms, and this midlatitude observation, well away from the auroral oval, extends the region over which meteorological effects of EEPs need to be assessed. Our findings underline the value of balloon measurements in providing rapid response to space weather events. The energy‐discriminating and altitude‐sensitive capability of the microscintillator augments spacecraft observations from below.

Comparison of the Results on Precipitation of High-Energy Electrons in the Stratosphere and on Satellites

Energetic electron precipitation (EEP) into the atmosphere is one of the mechanisms of depleting the Earth’s outer radiation belt. Precipitating electrons generate bremsstrahlung that penetrates the stratosphere and is recorded by detectors on balloons. However, these observations can be carried out only when the balloon is located at altitudes higher than ~20 km. The near-Earth POES satellites are constantly recording the fluxes of precipitating electrons in the loss cone, but they move too quickly in the space. In this paper, EEPs are compared on the basis of observations in the stratosphere and on satellites during 2003 and estimates of a number of EEP events at Apatity are obtained, assuming that the radiosonde was continuously located at an altitude higher than 26 km.

Temporal Characteristics of Energetic Magnetospheric Electron Precipitation as Observed During Long‐Term Balloon Observations

AbstractThe paper summarizes the properties of precipitation of magnetospheric electrons with energy above several hundred keV recorded by observing X‐ray bremsstrahlung in the polar stratosphere above the Murmansk region, Russia, in 1961–2019. Precipitation occurrence rate demonstrates a clear dependence on the solar activity with a maximum at the decay phase of the 11‐year solar cycle, similarly to the variability in occurrences of the high‐speed solar wind streams (HSSWS). The energetic electron precipitation (EEP) event series is often initiated by a moderate geomagnetic storm caused by a HSSWS and continues during geomagnetic storm recovery. EEP demonstrates the seasonal rate variation with the maxima in occurrence rate around the spring and the autumn solstices and correlates with fluences of relativistic electrons in the outer radiation belt. For 59 years, 589 events of precipitation were observed. Analysis of the long‐term time series revealed a growing trend in the rate of precipitation occurrence, especially in the 1990s to 2000s that is not properly explained yet.

Energetic Electron Precipitation Occurrence Rates Determined Using the Syowa East SuperDARN Radar

AbstractWe demonstrate that the Super Dual Auroral Radar Network (SuperDARN) radar at Syowa station, Antarctica, can be used to detect high frequency radio wave attenuation in the D region ionosphere during energetic electron precipitation (EEP) events. EEP‐related attenuation is identified in the radar data as a sudden reduction in the backscatter power and background noise parameters. We focus initially on EEP associated with pulsating aurora and use images from a colocated all‐sky camera as a validation data set for the radar‐based EEP event detection method. Our results show that high‐frequency attenuation that commences during periods of optical pulsating aurora typically continues for 2–4 hr after the camera stops imaging at dawn. We then use the radar data to determine EEP occurrence rates as a function of magnetic local time (MLT) using a database of 555 events detected in 2011. EEP occurrence rates are highest in the early morning sector and lowest at around 15:00–18:00 MLT. The postmidnight and morning sector occurrence rates exhibit significant seasonal variations, reaching approximately 50% in the winter and 15% in the summer, whereas no seasonal variations were observed in other MLT sectors. The mean event lifetime determined from the radar data was 2.25 hr, and 10% of events had lifetimes exceeding 5 hr.

Are EEP Events Important for the Tertiary Ozone Maximum?

AbstractEnergetic particle precipitation (EPP) increases the production of odd hydrogen (HOX) species in the mesosphere, which catalytically destroy ozone (O3) in sunlight. Hence, the EPP‐HOX impact on the tertiary O3 maximum (TOM) depends on a complex geometry of a geographic‐oriented TOM, geomagnetic‐oriented auroral zone, producing short‐lived HOX species, and a destruction process depending on the solar zenith angle (SZA). Particle observations from the Medium Energy Proton and Electron Detectors telescopes aboard the Polar Orbiting Environmental Satellites, and hydroxyl (OH) and O3 mixing ratios from Aura microwave limb sounder (MLS) are used to investigate the potential limitations of using the MLS observations to study EPP‐OH impact on the TOM in the Northern Hemisphere. Our results show limited overlap between the auroral zone and the TOM at twilight conditions. A composite analysis indicates O3 mixing ratio decrease over the auroral zone lagged by ∼1 day compared to the maximum energetic electron precipitation (EEP)‐OH impact. Hence, MLS is predominantly observing a lagged and lower estimate of the response of O3 to EEP‐OH at SZA > 95°. The EEP impact region within the TOM is smaller than the overlap region, strongly modulated by the background atmospheric dynamics. The results, although limited by the satellites viewing conditions, imply that the importance of EEP upon O3 mixing ratio is strongly influenced by the background atmosphere, both in terms of chemistry and dynamics. Multisatellite observations at different solar local times are required to separate the direct from the lagged EEP‐OH impact on O3.

Mesospheric Nitric Acid Enhancements During Energetic Electron Precipitation Events Simulated by WACCM‐D

AbstractWhile observed mesospheric polar nitric acid enhancements have been attributed to energetic particle precipitation through ion cluster chemistry in the past, this phenomenon is not reproduced in current whole‐atmosphere chemistry‐climate models. We investigate such nitric acid enhancements resulting from energetic electron precipitation events using a recently developed variant of the Whole Atmosphere Community Climate Model (WACCM) that includes a sophisticated ion chemistry tailored for the D‐layer of the ionosphere (50–90 km), namely, WACCM‐D. Using the specified dynamics mode, that is, nudging dynamics in the troposphere and stratosphere to meteorological reanalyses, we perform a 1‐year‐long simulation (July 2009–June 2010) and contrast WACCM‐D with the standard WACCM. Both WACCM and WACCM‐D simulations are performed with and without forcing from medium‐to‐high energy electron precipitation, allowing a better representation of the energetic electrons penetrating into the mesosphere. We demonstrate the effects of the strong particle precipitation events which occurred during April and May 2010 on nitric acid and on key ion cluster species, as well as other relevant species of the nitrogen family. The 1‐year‐long simulation allows the event‐related changes in neutral and ionic species to be placed in the context of their annual cycle. We especially highlight the role played by medium‐to‐high energy electrons in triggering ion cluster chemistry and ion‐ion recombinations in the mesosphere and lower thermosphere during the precipitation event, leading to enhanced production of nitric acid and raising its abundance by 2 orders of magnitude from 10−4 to a few 10−2 ppb.

Response of the total ozone to energetic electron precipitation events

In this paper we investigate response of the total ozone column to energetic electron precipitation (EEP) observed by bremsstrahlung effect. The list of EEP events was prepared by members of the balloon experiments of the Lebedev Physical Institute. Here we used superposed epoch analysis and the days with EEP events are registered during winter (November–February) and summer (June–August) months from 1970 to 2012 were chosen as key dates. This period corresponds approximately to three solar cycles. Data of the total ozone column were collected by single coherent total ozone dataset, called the Multi Sensor Reanalysis (MSR). A long series of data of the total ozone column is allowed us to study the response of ozone content to 90 winter and 103 summer EEP events. The obtained ozone sensitivity to the events of energetic electron precipitation is clearly pronounced during local winters in the high latitudes of the Northern and Southern Hemispheres (60–80 NH and 60–80 SH). In the high latitudes of the Northern Hemisphere, during winter months, the total ozone content can be reduced by up to 10 DU after energetic electron precipitation with minimum observed on the first day after EEP events. Response of the total ozone, over high latitudes of the Northern Hemisphere, to EEP events can be opposite during summer months.

Direct and indirect electron precipitation effect on nitric oxide in the polar middle atmosphere, using a full‐range energy spectrum

AbstractIn April 2010, a coronal mass ejection and a corotating interaction region on the Sun resulted in an energetic electron precipitation event in the Earth's atmosphere. We investigate direct and indirect nitric oxide (NO) response to the electron precipitation. By combining electron fluxes from the Total Energy Detector and the Medium Energy Proton and Electron Detector on the National Oceanic and Atmospheric Administration's Polar‐orbiting Operational Environmental Satellites, we obtain a continuous energy spectrum covering 1–750 keV. This corresponds to electrons depositing their energy at atmospheric altitudes 60–120 km. Based on the electron energy deposition, taking into account loss due to photolysis, the accumulated NO number density is estimated. When compared to NO measured at these altitudes by the Solar Occultation for Ice Experiment instrument on board the Aeronomy of Ice in the Mesosphere satellite, the NO direct effect was detected down to 55 km. The main variability at these altitudes is, however, dominated by the indirect effect, which is downward transported NO. We estimate the source of this descending NO to be in the upper mesosphere at ∼75–90 km.

Statistical characteristics of potentially chorus‐driven energetic electron precipitation from POES observations

AbstractIn this paper, using the Polar Orbiting Environment Satellites (POES) in the year 2011, we present global distributions of energetic electron precipitation (EEP) events that may be driven by lower band chorus waves. Since the footprint of plasmapause in the ionospheric height can basically be equal to midlatitude trough minimum, it can be identified through the global total electron content map. Then we distinguish events perhaps driven by chorus waves outside the plasmapause or those driven by hiss waves inside the plasmapause. Based on the simultaneous observations of EEP in the E1 0° (>30 keV) and E2 0° (>100 keV) channels from POES satellites, a total of 4455 potentially chorus‐driven events are identified. The potentially chorus‐driven events are mainly distributed from midnight to noon which is similar to the distribution of lower band chorus waves. As the level of geomagnetic substorm activity increases, the occurrence rate is higher, which could be due to excitation of chorus waves associated with substorm electron injection. During higher level of substorm, a large number of events occur in lower L shells. Besides, since the magnetosphere on the dayside is compressed and strong chorus waves are limited to the region where the ratio between the plasma frequency and electron gyrofrequency is less than 5, under the strong substorm, the events on the nightside are confined to lower L shells due to smaller electron gyrofrequencies relative to those on the dayside. The occurrence rate of the events on the dayside also increases with enhancement of solar wind dynamic pressure, which suggests that the solar wind dynamic pressure can contribute to the excitation of events on the dayside. The statistics of potentially chorus‐driven events are helpful to analyze the distribution of lower band chorus waves and their contributions to the loss of energetic electrons in the inner magnetosphere.

Energetic electron precipitation characteristics observed from Antarctica during a flux dropout event

AbstractData from two autonomous VLF radio receiver systems installed in a remote region of the Antarctic in 2012 is used to take advantage of the juxtaposition of the L = 4.6 contour, and the Hawaii‐Halley, Antarctica, great circle path as it passes over thick Antarctic ice shelf. The ice sheet conductivity leads to high sensitivity to changing D region conditions, and the quasi constant L shell highlights outer radiation belt processes. The ground‐based instruments observed several energetic electron precipitation events over a moderately active 24 h period, during which the outer radiation belt electron flux declined at most energies and subsequently recovered. Combining the ground‐based data with low and geosynchronous orbiting satellite observations on 27 February 2012, different driving mechanisms were observed for three precipitation events with clear signatures in phase space density and electron anisotropy. Comparison between flux measurements made by Polar‐orbiting Operational Environmental Satellites (POES) in low Earth orbit and by the Antarctic instrumentation provides evidence of different cases of weak and strong diffusion into the bounce loss cone, helping to understand the physical mechanisms controlling the precipitation of energetic electrons into the atmosphere. Strong diffusion events occurred as the <600 keV fluxes began to recover as a result of adiabatic transport of electrons. One event appeared to have a factor of about 10 to 100 times more flux than was reported by POES, consistent with weak diffusion into the bounce loss cone. Two events had a factor of about 3 to 10 times more >30 keV flux than was reported by POES, more consistent with strong diffusion conditions.

Comparison of modeled and observed effects of radiation belt electron precipitation on mesospheric hydroxyl and ozone

Observations have shown that mesospheric hydroxyl (OH) is affected by energetic electron precipitation (EEP) at magnetic latitudes connected to the outer radiation belt. It is not clear, however, if the current satellite‐based electron flux observations can be used to accurately describe EEP in atmospheric models. We use the Sodankylä Ion and Neutral Chemistry (SIC) model to reproduce the changes in OH and ozone observed by the Microwave Limb Sounder (MLS/Aura) during four strong EEP events. The daily mean electron energy‐flux spectrum, needed for ionization rate calculations, is determined by combining the Medium Energy Proton and Electron Detector fluxes and spectral form from the instrument for the detection of particles high‐energy electron detector on board the DEMETER satellite. We show that in general SIC is able to reproduce the observed day‐to‐day variability of OH and ozone. In the lower mesosphere, the model tends to underestimate the OH concentration, possibly because of uncertainties in the electron spectra for energies >300 keV. The model predicts OH increases at 60–80 km, reaching several hundred percent at 70–80 km during peak EEP forcing. Increases in OH are followed by ozone depletion, up to several tens of percent. The magnitude of modeled changes is similar to those observed by MLS and comparable to effects of individual solar proton events. Our results suggest that the combined satellite observations of electrons can be used to model the EEP effects above 70 km during geomagnetic storms, without a need for significant adjustments. However, for EEP energies >300 keV impacting altitudes <70 km, correction factors may be required.

Contrasting the responses of three different ground‐based instruments to energetic electron precipitation

In order to make best use of the opportunities provided by space missions such as the Radiation Belt Storm Probes, we determine the response of complementary subionospheric radiowave propagation measurements (VLF), riometer absorption measurements, cosmic noise absorption, and GPS‐produced total electron content (vTEC) to different energetic electron precipitation (EEP). We model the relative sensitivity and responses of these instruments to idealized monoenergetic beams of precipitating electrons, and more realistic EEP spectra chosen to represent radiation belts and substorm precipitation. In the monoenergetic beam case, we find riometers are more sensitive to the same EEP event occurring during the day than during the night, while subionospheric VLF shows the opposite relationship, and the change in vTEC is independent. In general, the subionospheric VLF measurements are much more sensitive than the other two techniques for EEP over 200 keV, responding to flux magnitudes two‐three orders of magnitude smaller than detectable by a riometer. Detectable TEC changes only occur for extreme monoenergetic fluxes. For the radiation belt EEP case, clearly detectable subionospheric VLF responses are produced by daytime fluxes that are ∼10 times lower than required for riometers, while nighttime fluxes can be 10,000 times lower. Riometers are likely to respond only to radiation belt fluxes during the largest EEP events and vTEC is unlikely to be significantly disturbed by radiation belt EEP. For the substorm EEP case both the riometer absorption and the subionospheric VLF technique respond significantly, as does the change in vTEC, which is likely to be detectable at ∼3–4 total electron content units.

Precipitating electron events in October 2003 as observed in the polar atmosphere

Balloon cosmic ray measurements at polar latitudes (Apatity station, geomagnetic vertical cutoff rigidity R c = 0.6 GV, invariant latitude Λ = 65°, and Mirny observatory, Antarctica, R c = 0.03 GV, Λ = −77°) in October 2003 were analysed. During this period, several energetic electron precipitation events were recorded via the bremsstrahlung generated by the electrons in the atmosphere. In order to determine the flux and the energy spectrum of precipitating electrons on the atmospheric boundary the simulation of electron and X-ray transport in the atmosphere was performed using the Geant4 Monte Carlo code. By comparing the results of balloon measurements with the simulation results, we deduced the precipitating electron flux during the 22 October 2003 event as J e ( E) = 7.7 × 10 6 exp (− E/12 keV), cm −2 s −1 keV −1.

LONG-TERM BALLOON COSMIC RAY EXPERIMENT: RESULTS OF ANALYSIS OF ENERGETIC ELECTRON PRECIPITATION EVENTS

More than 500 energetic Electron Precipitation Events were observed in the Earth's Northern and Southern polar atmosphere during a long-term cosmic ray balloon experiment. The results of analysis of these events allow to show (1) distribution of occurrence rate of EPEs within solar activity cycle, (2) semiannual variation in the EPE occurrence, (3) interplanetary and geomagnetic conditions related to the EPEs in the atmosphere.

Atmospheric response to NOy source due to energetic electron precipitation

We have introduced additional NOy sources caused by energetic electron precipitation (EEP) during 1987 into a Chemistry‐Climate model. Comparison of two model runs with and without EEP reveals increase of reactive nitrogen by about 2 ppbv in the middle stratosphere over the tropical and middle latitudes. In the upper stratosphere over the polar winter regions the simulated NOy enhancement reaches 10 ppbv. Decreases of the ozone mixing ratio in the stratosphere by up to 5% over midlatitudes and up to 30% over southern high‐latitudes are calculated. A ∼0.5 K cooling in the middle stratosphere over the tropics and up to 2 K over southern high‐latitudes is calculated with detectable changes in the surface air temperatures. These results confirm that the magnitude of the atmospheric response to EEP events can potentially exceed the effects from solar UV fluxes. These mechanisms work in phase outside polar latitudes, but can compensate each other within polar latitudes.

Characteristics of energetic electron precipitation into the earth's polar atmosphere and geomagnetic conditions

A number of energetic electron precipitation events (EPEs) were observed in the Earth's polar atmosphere (Murmansk region, geographical coordinates 68.57 N, 33.03 E and Mirny, Antarctica, 66.34 S, 92.55 E) during the long-term cosmic ray balloon experiment from 1957 up to now. During geomagnetic storms significant X-ray fluxes caused by precipitating electrons at the top of the atmosphere sometimes penetrated to the atmospheric depth of 60 gcm −2 . We show that (1) there is a quasi-11-year cycle in EPE occurrence shifted with respect to solar activity cycle, and (2) the yearly rate of EPE occurrence has an ascending trend during the period 1965–1999. The EPE characteristics evaluated from the balloon experiment are compared with the available data on geomagnetic activity and the possible relations between the features of EPE events and geomagnetic conditions are discussed.

Spacecraft charging anomaly on a low-altitude satellite in an aurora

On May 5,1995, the microwave imager instrument aboard the Defense Meteorological Satellite Program F13 spacecraft experienced a lockup of its microprocessor unit. The anomaly is attributed to an electrical malfunction caused by an electrostatic discharge on the vehicle. It occurred during an intense energetic electron precipitation event within a region of very low plasma density in the auroral zone. Plasma measurements indicate that the spacecraft frame charged to a voltage near 459 V within a few seconds. Calculations of the capacitance of the ungrounded thermal blankets covering the surface of the spacecraft are consistent with a surface charging time of a few seconds to reach several kilovolts. Subsequent electrostatic discharge led to the lockup.

Downward mapping of quasi-static ionospheric electric fields at low latitudes during fair weather

The problem of downward mapping of equatorial ionospheric electric fields is studied in two dimensions employing the finite elements and finite differences numerical techniques. The solutions obtained for low latitudes are compared with known results for high latitudes. It is found that equatorial ionospheric electric fields of scale lengths of the order of 100 km or more reach balloon heights (30–40 km) without undergoing noticeable attenuation. However, in the case of equatorial ionospheric electric fields of scale lengths of a few tens of kilometers it is found that these fields reach balloon heights with severe attenuation. The corresponding attenuation factors are significantly larger than those known for high latitudes. It is also shown that the presence of mountains with a fairly large height as well as of a large-scale conductivity irregularity in the middle atmosphere, such as that expected in the South Atlantic Magnetic Anomaly (SAMA) region during energetic electron precipitation events, can considerably distort the mapped ionospheric electric fields at the middle atmosphere.