Specification of the Ionosphere-Thermosphere Environment Using Ensemble Kalman Filter with Orthogonal Transformations
Abstract:The Ionosphere-Thermosphere environment undergoes constant and
sometimes dramatic changes due to solar and geomagnetic activity.
Furthermore, given that this environment has a significant effect
on space infrastructure, such as satellites, it is important to
understand the potential changes caused by space weather events.
This work presents a case study of four time periods using
assimilation methods with the Global Ionosphere-Thermosphere Model
(GITM). The main objective is to analyze the changes in the global
upper atmospheric environment caused by extreme space weather
events, including the Halloween storm, and analyze the effect on
satellite drag and collision uncertainty. In particular, an
ensemble Kalman filter (EnKF) assimilation method is applied to
GITM and used to incorporate observations from the CHAllenging
Minisatellite Payload (CHAMP) and Gravity Recovery and Climate
Experiment (GRACE) missions. To reduce the introduction of noise
into the assimilation results, we use orthogonal transformations in
the EnKF to capture the dominant correlations within the model
variables. In particular, we use principal component analysis
technique to extract the dominant directions of variability and
form a basis for an orthogonal transformation. The assimilation is
performed in the space spanned by the orthogonal basis and used to
adjust the model variables and parameters.
The experiments show that key solar parameters, which act as proxy
for solar activity, exert a significant influence in the evolution
of the total atmospheric density. Furthermore, the results also
show the strong correlation that exists between upper atmospheric
density and solar activity. That is, the correlation is strong
during solar active times, and weak during solar quiet times.
Indicating that at active times the sun dominates the changes in
the ionosphere-thermosphere, while at quiet times internal
processes dominate the evolution of the ionosphere-thermosphere.
The work is part of the Integrated Modeling of Perturbations in
Atmospheres for Conjunction Tracking (IMPACT) project in Los Alamos