D-region impact area of energetic electron precipitation during pulsating aurora

A total of 10 radars from the Super Dual Auroral Radar Network (SuperDARN) in Antarctica were used to estimate the spatial area over which energetic electron precipitation (EEP) impacts the D-region ionosphere during pulsating aurora (PsA) events. We use an all-sky camera (ASC) located at Syowa Station to confirm the presence of optical PsAs, and then we use the SuperDARN radars to detect high frequency (HF) radio attenuation caused by enhanced ionisation in the D-region ionosphere. The HF radio attenuation was identified visually by examining quick-look plots of the background HF radio noise and backscatter power from each radar. The EEP impact area was determined for 74 PsA events. Approximately one-third of these events have an EEP impact area that covers at least 12∘ of magnetic latitude, and three-quarters cover at least 4∘ of magnetic latitude. At the equatorward edge of the auroral oval, 44 % of events have a magnetic local time extent of at least 7 h, but this reduces to 17 % at the poleward edge. We use these results to estimate the average size of the EEP impact area during PsAs, which could be used as a model input for determining the impact of PsA-related EEP on the atmospheric chemistry.

D-region impact area of energetic particle precipitation during pulsating aurora

Ten radars from the Super Dual Auroral Radar Network (SuperDARN) in Antarctica were used to estimate the spatial area over which energetic electron precipitation (EEP) impacts the D-region ionosphere during pulsating aurora (PsA) events. We use an all-sky camera located at Syowa Station to confirm the presence of optical PsA, and then use the SuperDARN radars to detect HF radio attenuation caused by enhanced ionisation in the D-region ionosphere. The HF radio attenuation was identified visually by examining quick-look plots of the background HF radio noise and backscatter power from each radar. The EEP impact area was determined for 74 PsA events. Approximately one third of these events have an EEP impact area that covers at least 12° of magnetic latitude, and three quarters cover at least 4° of magnetic latitude. At the equatorward edge of the auroral oval, 44 % of events have a magnetic local time extent of at least 7 hours, but this reduces to 17 % at the poleward edge. We use these results to estimate the average size of the EEP impact area during PsA, which could be used as a model input for determining the impact of PsA-related EEP on the atmospheric chemistry.

Climatology Characteristics of Ionospheric Irregularities Described with GNSS ROTI

At equatorial and high latitudes, the intense ionospheric irregularities and plasma density gradients can seriously affect the performances of radio communication and satellite-based navigation systems; that represents a challenging topic for the scientific and engineering communities and operational use of communication and navigation services. The GNSS-based ROTI (rate of TEC index) is one of the most widely used indices to monitor the occurrence and intensity of ionospheric irregularities. In this paper, we examined the long-term performance of the ROTI in terms of finding the climatological characteristics of TEC fluctuations. We considered the different scale temporal signatures and checked the general sensitivity to the solar and geomagnetic activity. We retrieved and analyzed long-term time-series of ROTI values for two chains of GNSS stations located in European and North-American regions. This analysis covers three full years of the 24th solar cycle, which represent different levels of solar activity and include periods of intense geomagnetic storms. The ionospheric irregularities’ geographical distribution, as derived from ROTI, shows a reasonable consistency to be found within the poleward/equatorward boundaries of the auroral oval specified by empirical models. During magnetic midnight and quiet-time conditions, the equatorward boundary of the ROTI-derived ionospheric irregularity zone was observed at 65–70° of north magnetic latitude, while for local noon conditions this boundary was more poleward at 75–85 magnetic latitude. The ionospheric irregularities of low-to-moderate intensity were found to occur within the auroral oval at all levels of geomagnetic activity and seasons. At moderate and high levels of solar activity, the intensities of ionospheric irregularities are larger during local winter conditions than for the local summer and polar day conditions. We found that ROTI displays a selective latitudinal sensitivity to the auroral electrojet activity—the strongest dependence (correlation R > 0.6–0.8) was observed within a narrow latitudinal range of 55–70°N magnetic latitude, which corresponded to a band of the largest ROTI values within the auroral oval zone expanded equatorward during geomagnetic disturbances.

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.

Surveying pulsating auroras

The early morning auroral oval is dominated by pulsating auroras. This category of aurora has often been discussed as if it is just one phenomenon, but it is 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 is found to be a nearly ubiquitous early morning aurora, and pulsating aurora is almost exclusively amorphous pre-midnight. Occurrence distributions for each type of pulsating aurora are mapped into the magnetosphere to approximately determine the location of their source regions. The patchy and patchy pulsating aurora distributions primarily map to locations approximately between 4 and 9 RE, while some amorphous pulsating aurora maps to farther distances.

A watercolor painting of northern lights seen above Japan on 11 February 1958

A 61 years old watercolor painting of red aurora was recently provided from a Japanese citizen, and it contributed to understand the detailed time evolution around the peak time of the large magnetic storm on 11 February 1958. The painting gives information of the elevation angle of the red aurora seen from low latitude (27.4° magnetic latitude) at 1205–1225 UT during the beginning of the recovery phase of the magnetic storm. Combined with the hand-made sketch of the same red aurora seen from the Abashiri Local Meteorological Office (located at 34° magnetic latitude) at 1215 UT, the position of the red aurora is determined via triangulation. It is found that the red aurora reached up to 400 km at 41° magnetic latitude, which is 1.0° higher in magnetic latitude than the red aurora which appeared just before the peak time of the magnetic storm.