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The Two‐Dimensional Evolution of Thermospheric ∑O/N 2 Response to Weak Geomagnetic Activity During Solar‐Minimum Observed by GOLD
Ist Teil von
Geophysical research letters, 2020-09, Vol.47 (18)
Erscheinungsjahr
2020
Quelle
Wiley-Blackwell Full Collection
Beschreibungen/Notizen
Abstract
We conduct observational and modeling studies of thermospheric composition responses to weak geomagnetic activity (nongeomagnetic storms). We found that the thermospheric O and N
2
column density ratio (∑O/N
2
) in part of the Northern Hemisphere measured by Global‐scale Observations of the Limb and Disk (GOLD) exhibited large and long‐lived depletions during weak geomagnetic activity in May and June 2019. The depletions reached 30% of quiet time values, extended equatorward to 10°N and lasted more than 10 hr. Furthermore, numerical simulation results are similar to these observations and indicate that the ∑O/N
2
depletions were pushed westward by zonal winds. The ∑O/N
2
evolution during weak geomagnetic activity suggests that the formation mechanism of the ∑O/N
2
depletions is similar to that during a geomagnetic storm. The effects of weak geomagnetic activity are often ignored but, in fact, are important for understanding thermosphere neutral composition variability and hence the state of the thermosphere‐ionosphere system.
Plain Language Summary
The column density ratio of O and N
2
(∑O/N
2
) has been used to monitor geomagnetic storm effects in the thermosphere, as well as providing valuable information about the ionosphere. This triggers an important question: Can weak geomagnetic activities cause changes in thermospheric composition too? Here, we conduct studies based on geostationary orbit observations and numerical simulations. Model outputs replicate the general morphology of this variability for the cases examined. This made it possible to understand the cause of the composition response to weak geomagnetic forcing. We found that the ∑O/N
2
depletion observed was pushed westward by the zonal wind. During weak geomagnetic activity, the ∑O/N
2
response is similar to the response during a geomagnetic storm, albeit it is weaker. In summary, our study suggests that weak geomagnetic activity can also generate strong and long‐lived responses in thermosphere composition during solar minimum and that this response can be important to understanding the thermosphere and ionosphere variability during the so‐called quiet times.
Key Points
The observed ∑O/N
2
exhibits strong and long‐lived response to weak geomagnetic activity
The numerical simulation results resemble the observed ∑O/N
2
responses during weak geomagnetic activity
Weak geomagnetic activity may have important effects on thermosphere‐ionosphere variability that cannot be simply ignored