Unexpected variations of the hydrogen in the upper thermosphere revealed by TIMED/GUVI: An important challenge in the ITM science
Abstract
Atomic hydrogen, H, is a key atmospheric constituent in the Earth's upper atmosphere. Understanding the global and temporal variations of this constituent is critical for nowcasting and forecasting the state of the Ionosphere/Thermosphere/Mesosphere (ITM) system, since those atoms are important participants in the ion-neutral coupling of the upper thermosphere and ionosphere. However, previous studies have shown that the existing climatological models (e.g., the NRLMSISE-00 model) cannot provide satisfactory predictions of the H distribution in the ITM region, in that differences between observations and models have long been documented in the literature. Without a better understanding the H distribution, our abilities to nowcast/forecast the ITM system are limited. To partially address this problem, we analyzed six years of TIMED/GUVI Lyman-α observations to quantify the H density variations in the upper thermosphere, which can provide systematic data constraints for better understanding the H variabilities in the ITM region. Our results revealed unexpected solar cycle, seasonal, and dawn-to-dusk variations of the H density when compared to those predicted by the NRLMSISE-00 model and the NRLMSIS 2.0 model [Wan et al., Solar cycle, seasonal, and dawn-to-dusk variations of the hydrogen in the upper thermosphere, JGR: Space Physics, 2022]. Those data-model discrepancies represent an important space weather challenge in the ITM science. We will discuss the details of those discrepancies as well as other associated challenges that need to be addressed for improving our abilities to nowcast/forecast the state of the ITM system, such as the lack of data constraints for development of more accurate empirical H density models, the lack of theoretical and modeling works to reconcile observations and models, and the needs for further developing and testing our understanding of the solar cycle variability of key atmospheric constituents (particularly H) and its physical drivers in the coming years.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMSA31C..01W