**4. Model inputs**

The inner state of the simulated space and external forcings acting on it are characterized by the model inputs set up by the user: (1) date and time to set an initial placement of the numerical grid nodes relative to the Sun; (2) spectra of the solar UV and EUV radiation; (3) fluxes of the high energetic electrons precipitating from the magnetosphere; (4) the FACs connecting the ionosphere with the magnetosphere and/or (5) the distribution of ϕ at the boundaries of the polar cap; (6) the local *j* → *s* flowing through the lower boundary from below; (7) indices of the geomagnetic activity and (8) components of the interplanetary magnetic field (IMF) and solar wind.

The solar UV and EUV spectra define the coefficients of O2 dissociation and O2 + , N2 + , NO<sup>+</sup> and O<sup>+</sup> production rates due to the photoionization of the corresponding neutral components. The UV and EUV spectra dependence on the solar activity is set up according to Ref. [16]. The intensity of the night scatter radiation intensity is 5 kR for the emission with wave length *λ* = 121.6 nm and 5 R for the rest emission lines (102.6, 58.4 and 30.4 nm).

The precipitating electrons' fluxes are set up at the upper boundary of the thermosphere, at 520 km, and their intensity *I* is written as:

$$I(\boldsymbol{\Phi}, \Lambda, \boldsymbol{E}) = I\_{\boldsymbol{m}}(\boldsymbol{E}) \exp \left[ - (\boldsymbol{\Phi} - \boldsymbol{\Phi}\_{\boldsymbol{m}}(\boldsymbol{E}))^2 / \Lambda \boldsymbol{\Phi} \left( \boldsymbol{E} \right)^2 - \left( \Lambda - \Lambda\_{\boldsymbol{m}}(\boldsymbol{E}) \right)^2 / \Lambda \Lambda \left( \boldsymbol{E} \right)^2 \right] \tag{32}$$

$$\boldsymbol{\Phi}\_{m} = (\boldsymbol{\Phi}\_{md} + \boldsymbol{\Phi}\_{m})/2 + \cos\Lambda (\boldsymbol{\Phi}\_{md} + \boldsymbol{\Phi}\_{m})/2,\tag{33}$$

The geomagnetic activity is used in the UAM by setting up the planetary geomagnetic indices *Kp* and *Ap*, indicating global geomagnetic field disturbance, and aurora indices *AE*, *AL* and *AU*, where *AU* and *AL* indicate, respectively, the largest increase and lowest decrease of the Northern component of the geomagnetic field in comparison to the background (quiet) value, *AE* is the sum of *AL* and *AU* and characterizes the largest scale of the magnetic field during

The UAM provides the possibility of integrating various empirical models and data of the upper atmosphere. The comparison of the self-consistent UAM version and the UAM versions with different combinations of the empirical models allows testing both the UAM and the

spheric circulation is calculated by the numerical solution of Eqs. (6) and (8) where ∇*p* from

In the UAM-HWM version the distribution of the horizontal thermospheric wind is calculated using the empirical model HWM-93 [13]. The vertical component of the wind velocity is calculated by the numerical solution of the continuity equation for *ρ* (Eq. (8)). The HWM-93 is used for the set of the initial conditions and for comparison of the theoretical model winds

The magnetospheric block of the UAM simulates the transport processes in the plasma sheet by solving the system of the equations for the plasma sheet ions (see item 2). In Ref. [21],

There are several ways to set up FACs spatial-temporal distributions in the UAM, such as empirical data from the magnetic field measurements from the Dynamics Explorer 2 [22] and the Magsat satellites [23], the FACs empirical models by Papitashvili [24] in [25, 26], by Lukianova [27] in Ref. [28] and MFACE [29] in Ref. [30]. All these versions with various FACs take into account the dependence of FACs on the interplanetary magnetic field (IMF). Such methods of setting the FACs distribution allow using any other empirical data

In the UAM version [31], the positions of the auroral oval boundaries, the values of electron flux intensities and the latitudes and longitudes of the intensity maxima were set from precipitation patterns observed by DMSP. The spectra of the precipitating electrons are assumed

The UAM-P version [32, 33], created in Potsdam, differs from the UAM by the electric field block simulation. This block uses magnetic dipole coordinates instead of spherical geographical

 = 0, 4 nPa and *ni*

solution is not stable, and it falls apart after approximately 1 h.

and *Tn* are calculated directly from the MSIS [11]. The thermo-

The Global Numerical Model of the Earth's Upper Atmosphere

http://dx.doi.org/10.5772/intechopen.71139

13

at the lower boundary and initial

 = 0, 4 cm−3, correspondingly. The program

distribution and R2 FACs. The problem is that the obtained

and *nn*

the substorm in the high-latitude regions.

the MSIS is used. Finally, the MSIS is used to set up *Tn*

**5. The UAM versions**

In the UAM-MSIS version, *nn*

the initial values are taken as *pi*

produces more or less realistic *pi*

to be Maxwellian in this case.

empirical models.

conditions as well.

with observations.

of FACs.

where *Φ* and *Λ* are the geomagnetic latitude and longitude, respectively (*Λ* = 0 corresponds to the midday magnetic meridian); *E* is the energy of the precipitating electrons; *Im*(*E*) is the maximum intensity of the precipitating electron flux; ∆*Φ* and ∆*Λ* are the half-widths of the maximum precipitations in latitude and longitude; *Φmd* and *Φmn* are the magnetic latitudes of the maximum precipitations at the midday and midnight meridians, respectively. Specific values for the precipitating parameters in Eqs. (32) and (33) are taken from the empirical models [17, 18].

The magnetospheric sources *j* → *<sup>m</sup>* in Eq. (27a) specify the distribution of FACs. The FACs of the Region 1 (R1) flow from the magnetosphere into the ionosphere on the dawn side and out of the ionosphere on the dusk side, at latitudes higher ±75°. The FACs of the Region 2 (R2) flow in the opposite direction, at areas equatorward of the R1 currents. The distribution of current densities depends on the geophysical conditions and is setup in the UAM in several different ways depending on the task, either as distribution of the FACs in the R1, 2 and the cusp region according to the model [19], or as the distribution of electric potential at the boundary of the polar cap [20] with the FACs in the cusp region and the R2.

The so-called seismogenic electric currents are the vertical electric currents switched on to simulate the ionosphere effects of various mesoscale phenomena in the lower ionosphere, such as earthquakes, thunderstorms, etc. Used as a model input, the vertical *j* → *s* are added locally to Eq. (27a) at the lower boundary of the UAM.

The geomagnetic activity is used in the UAM by setting up the planetary geomagnetic indices *Kp* and *Ap*, indicating global geomagnetic field disturbance, and aurora indices *AE*, *AL* and *AU*, where *AU* and *AL* indicate, respectively, the largest increase and lowest decrease of the Northern component of the geomagnetic field in comparison to the background (quiet) value, *AE* is the sum of *AL* and *AU* and characterizes the largest scale of the magnetic field during the substorm in the high-latitude regions.
