Completion of a whole atmosphere-ionosphere coupled model
Systematically coupled atmospheric, ionospheric and electrodynamics models to successfully develop the world’s first numerical model capable of handling the entire global atmospheric region, ranging from the troposphere through the ionosphere. The model was named GAIA for short (acronym meaning Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy).
Reproduction of ionospheric longitudinal variation and understanding vertical coupling processes in the Earth’s atmosphere
It was proved that the persistent wavenumber-4 structure in the ionospheric longitudinal variation as recently observed by artificial satellites can be reproduced by the atmosphere-ionosphere coupled simulation. Moreover, the simulation found that certain atmospheric tidal components, which constitute a basis of the wavenumber-4 structure, are excited by convective activities in the troposphere and then propagate to the thermosphere, thereby influencing the ionosphere through electrodynamic dynamo action (Figure 1). The simulation also indicates that meteorological activity in the lower atmosphere is one important cause of daily ionospheric variations [Jin et al., 2011].
Figure 1：Vertical atmospheric coupling reproduced by the GAIA model [Jin et al., 2011]
Reproduction of the "equatorial anomaly" in thermospheric distribution and understanding the causes thereof
The peak electron density of the ionospheric F-region is known to appear at geomagnetic latitude of ±10 to 15 degrees, but not at the equator where sunlight intensity is the highest (so-called "equatorial ionization anomaly"). Recent observations by artificial satellites have also clarified the presence of an "equatorial anomaly” structure in thermospheric distribution similar to that in the ionosphere, raising ongoing discussions about what causes the structure to form. We conducted an atmosphere-ionosphere coupled simulation and found that the model also reproduced the equatorial anomaly not only in the ionosphere but also in the thermosphere (Figure 2). Detailed analyses then revealed something new for us to consider: in addition to the effects from interaction between the neutral atmosphere and ionospheric plasma, atmospheric tides directly propagating from the lower atmosphere to the upper thermosphere are attributed to the formation of the thermospheric equatorial anomaly. Furthermore, the wavenumber-4 longitudinal structure was also found to appear not only in the ionosphere but also in the upper thermosphere, suggesting that the lower atmosphere significantly influences the upper atmosphere [Miyoshi et al., 2011].
Figure 2： Equatorial anomaly in thermosphere：(Upper) Observation by CHAMP satellite [Liu et al., 2010]. (Lower) Simulation by GAIA model [Miyoshi et al., 2011].
Reproduction of upper atmospheric phenomena through high-resolution simulations
A high spatial resolution version of atmospheric model has been developed, which was found to have ability to reproduce gravity waves with their wavelength of several hundreds to thousands of km, along with their excitation in the troposphere and propagation to the thermosphere. Miyoshi and Fujiwara [2009] studied the features of gravity waves in the thermosphere by using the model, and then clarified the relation of gravity waves with longitudinally dependent convective activities in the lower atmosphere. Jin et al. [2011] incorporated the results from the high-resolution atmospheric model into the highly resolved electrodynamics model, and showed that the effects of gravitational waves in the thermosphere are apparent in the distribution of ionospheric electric fields.
Shinagawa et al. [2009] developed a high resolution version of ionospheric model and conducted simulations on the ionosphere at the time of the total solar eclipse on July 22, 2009, thereby clarifying the influence of a solar eclipse on the ionosphere (including displacement of the region with reduced electron density due to displacement of the moon’s shadow) from both the model and observations of TEC (total electron content) above the Japanese archipelago.
Comparison of observations with atmosphere-ionosphere coupled simulations into which meteorological reanalysis data is assimilated
A method has been developed to assimilate meteorological reanalysis data into the tropospheric and stratospheric portion of GAIA. With regard to daily variation of solar radiation, the F10.7 index actually observed is adopted in the model. As a result, a realistic modeling of the upper atmosphere has been realized, including influences from the actual lower atmosphere. This model was being used to conduct long-term simulations (several months so far), and compared with global satellite observations for validation. Jin et al. [2010, 2011] reported the initial results, indicating that the GAIA model offers good reproducibility regarding location of the equatorial anomaly and north-south asymmetry.
Completion of a whole atmosphere-ionosphere coupled model
Systematically coupled atmospheric, ionospheric and electrodynamics models to successfully develop the world’s first numerical model capable of handling the entire global atmospheric region, ranging from the troposphere through the ionosphere. The model was named GAIA for short (acronym meaning Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy).
Reproduction of ionospheric longitudinal variation and understanding vertical coupling processes in the Earth’s atmosphere
It was proved that the persistent wavenumber-4 structure in the ionospheric longitudinal variation as recently observed by artificial satellites can be reproduced by the atmosphere-ionosphere coupled simulation. Moreover, the simulation found that certain atmospheric tidal components, which constitute a basis of the wavenumber-4 structure, are excited by convective activities in the troposphere and then propagate to the thermosphere, thereby influencing the ionosphere through electrodynamic dynamo action (Figure 1). The simulation also indicates that meteorological activity in the lower atmosphere is one important cause of daily ionospheric variations [Jin et al., 2011].
Reproduction of the "equatorial anomaly" in thermospheric distribution and understanding the causes thereof
The peak electron density of the ionospheric F-region is known to appear at geomagnetic latitude of ±10 to 15 degrees, but not at the equator where sunlight intensity is the highest (so-called "equatorial ionization anomaly"). Recent observations by artificial satellites have also clarified the presence of an "equatorial anomaly” structure in thermospheric distribution similar to that in the ionosphere, raising ongoing discussions about what causes the structure to form. We conducted an atmosphere-ionosphere coupled simulation and found that the model also reproduced the equatorial anomaly not only in the ionosphere but also in the thermosphere (Figure 2). Detailed analyses then revealed something new for us to consider: in addition to the effects from interaction between the neutral atmosphere and ionospheric plasma, atmospheric tides directly propagating from the lower atmosphere to the upper thermosphere are attributed to the formation of the thermospheric equatorial anomaly. Furthermore, the wavenumber-4 longitudinal structure was also found to appear not only in the ionosphere but also in the upper thermosphere, suggesting that the lower atmosphere significantly influences the upper atmosphere [Miyoshi et al., 2011].
Reproduction of upper atmospheric phenomena through high-resolution simulations
A high spatial resolution version of atmospheric model has been developed, which was found to have ability to reproduce gravity waves with their wavelength of several hundreds to thousands of km, along with their excitation in the troposphere and propagation to the thermosphere. Miyoshi and Fujiwara [2009] studied the features of gravity waves in the thermosphere by using the model, and then clarified the relation of gravity waves with longitudinally dependent convective activities in the lower atmosphere. Jin et al. [2011] incorporated the results from the high-resolution atmospheric model into the highly resolved electrodynamics model, and showed that the effects of gravitational waves in the thermosphere are apparent in the distribution of ionospheric electric fields.
Shinagawa et al. [2009] developed a high resolution version of ionospheric model and conducted simulations on the ionosphere at the time of the total solar eclipse on July 22, 2009, thereby clarifying the influence of a solar eclipse on the ionosphere (including displacement of the region with reduced electron density due to displacement of the moon’s shadow) from both the model and observations of TEC (total electron content) above the Japanese archipelago.
Comparison of observations with atmosphere-ionosphere coupled simulations into which meteorological reanalysis data is assimilated
A method has been developed to assimilate meteorological reanalysis data into the tropospheric and stratospheric portion of GAIA. With regard to daily variation of solar radiation, the F10.7 index actually observed is adopted in the model. As a result, a realistic modeling of the upper atmosphere has been realized, including influences from the actual lower atmosphere. This model was being used to conduct long-term simulations (several months so far), and compared with global satellite observations for validation. Jin et al. [2010, 2011] reported the initial results, indicating that the GAIA model offers good reproducibility regarding location of the equatorial anomaly and north-south asymmetry.