Speaker
Description
In polar latitudes, energetic electron precipitation (EEP; energies ~10s of keV to a few MeV) originating from the radiation belts and plasma sheet has a significant impact on the neutral composition and chemistry of the atmosphere in the mesosphere–lower thermosphere (∼60– 120 km) region. Precipitating electrons greatly disturb the atmospheric concentrations of odd nitrogen (NOx) and odd hydrogen (HOx) species, which in turn contribute to ozone depletion in the mesosphere and stratosphere. Despite its importance for atmospheric chemistry and vertical coupling processes, EEP is not accurately represented in solar forcing inputs used by Coupled Model Intercomparison Project (CMIP) climate models. In particular, uncertainties in EEP-driven ionization rates contribute to biases in the simulated atmospheric response.
This study presents a validation of EEP forcing in climate models at both local and global scales using ground based and satellite measurements. Local validation is performed by directly comparing modeled ionization rate (or electron density) profiles from Whole Atmosphere Community Climate Model (WACCM) with those derived from EISCAT-VHF incoherent scatter radar at Tromsø and rocket measurements carried out at Andøya and Esrange.
To study the EEP forcing at different longitudes, we use Arase satellite pitch angle–sorted electron flux data within the 0-10° pitch angle bin (encompassing both precipitating and trapped electron populations) and spanning energies from a few keV to ~1 MeV. The Arase energy–flux spectra obtained during EISCAT conjunction intervals are converted into (1) ionization rates and subsequently (2) electron density profiles using a forward modeling approach. The Arase energy-flux spectra are then scaled inorder to get the electron density profile that match best to the EISCAT observations during conjunction intervals. The derived energy dependent scaling factors are then applied to Arase measurements at similar L-shells, enabling the extension of EEP characterization across different longitudes.
Based on coordinated satellite and ground-based measurements, we address key questions related to EEP, including the quantification of EEP flux input into the Earth’s upper atmosphere and the characterization of its variability as a function of geomagnetic activity and magnetic local time.
Co-author list:
Antti Kero, Pekka Verronen, Yoshizumi Miyoshi, Joshua Fadiji, Shiang-Yu Wang, Yoichi Kazama, C-W. Jun, Satoshi Kasahara, Shoichiro Yokota, Kunihiro Keika, Tomoaki Hori, Takefumi Mitani, Takeshi Takashima, Ayako Matsuoka, Mariko Teramoto, Kazuhiro Yamamoto, Iku Shinohara