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Global comparison of the model results of GSM TIP with IRI for summer conditions
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Advances in Space Research 43 (2009) 1633–1637 www.elsevier.com/locate/asr
Global comparison of the model results of GSM TIP with IRI for summer conditions Yu N. Korenkov *, V.V. Klimenko, F.S. Bessarab WD IZMIRAN, Pobedy av., 41, 236017 Kaliningrad, Russia Received 21 November 2007; received in revised form 7 August 2008; accepted 7 August 2008
Abstract This paper presents the results of the numerical calculations thermosphere/ionosphere parameters which were executed with using of the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP)and comparison of these results with empirically-based model IRI-2001. Model GSM TIP was developed in West Department of IZMIRAN and solves self-consistently the time-dependent, 3-D coupled equations of the momentum, energy and continuity for neutral particles (O2, N2, O), ions (O+, H+), molecular ions (M+) and electrons and largescale eletric field of the dynamo and magnetospheric origin in the range of height from 80 km to 15 Earth’s radii. The empirically derived IRI model describes the E and F regions of the ionosphere in terms of location, time, solar activity and season. Its output provides a global specification not only of Ne but also on the ion and electron temperatures and the ion composition. These two models represent a unique set of capabilities that reflect major differences in along with a substantial approaches of the first-principles model and global database model for the mapping ionosphere parameters. We focus on global distribution of the Ne, Ti, Te and TEC for the one moment UT and fixed altitudes: 110 km, hmF2, 300 km and 1000 km. The calculations were executed with using of GSM TIP and IRI models for August 1999, moderate solar activity and quiet geomagnetic conditions. Results present as the global differences between the IRI and GSM TIP models predictions. The discrepancies between model results are discussed. Ó 2009 Published by Elsevier Ltd on behalf of COSPAR. Keywords: Ionospheric parameters; Theoretical model; IRI; Global comparison
1. Introduction The main physical principles of the terrestrial ionosphere are reasonably well understood and are described by a set of appropriate equations of plasma hydrodynamics (Schunk, 1988). Investigations of the ionospheric processes by solving the first principles equations have some degree of success as shown by comparisons of the model results with observations and empirical ionospheric model (e.g. IRI). The discrepancies between theoretical and empirical models outputs are frequently attributed inadequate constrains on the model inputs or to mathematical simplifications of some physical processes. Hence, the capabilities of an individual theoretical model to describe adequately the *
Corresponding author. E-mail address: [email protected] (Y.N. Korenkov).
0273-1177/$36.00 Ó 2009 Published by Elsevier Ltd on behalf of COSPAR. doi:10.1016/j.asr.2008.08.016
experimental data are a good test of the validity of the mathematical model. Efforts to validate ionospheric models and to do comparisons between them have been initiated by many authors (e.g. Szuszczewicz et al., 1992, 1996; Meza et al., 2002; Fesen et al., 2002). In this paper, we make use of the first principle global model GSM TIP, developed in WD IZMIRAN, Kaliningrad, to simulate global distributions of the ionospheric parameters for August 1999, geomagnetic quiet condition and comparison of the model output with empirical IRI model (Bilitza, 2001). 2. Brief GSM TIP description The global self-consistent model of the thermosphere, ionosphere and protonosphere was developed in the West Department of IZMIRAN of the Russian Academy of Sci-
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ence. For given input data the model calculates the timedependent global three-dimensional structure of the temperature, composition (O2, N2, O), and vector velocity of the neutral atmosphere and of the densities, temperatures, and vector velocities of atomic (O+, H+) and molecular ions and two-dimensional distribution of the electric field potential both of dynamo and magnetospheric origin. The solution is performed numerically on a global grid with resolutions of 5° in latitude and 15° in longitude in spherical geomagnetic coordinate system. In the vertical dimension, the thermospheric code uses 30 grid points between 80 and 520 km altitude above the Earth’s surface. The ionospheric part of the code (F2 region and upper ionosphere) has variable spatial steps along the magnetic field lines from a base altitude of 175 km to a maximum distance of 15 Earth radii. Note here that ionospheric code is not necessary upper boundary conditions. Model inputs are: (1) the solar UV and EUV spectra, (2) the precipitating electron fluxes, and (3) the distribution of the field-aligned currents in the first and second high-latitude region. The model has been described in detail by Namgaladze et al. (1988, 1991) and its application has been presented in the papers (Korenkov et al.,1996, 1998). 3. Input data and results In our model the first region of the field-aligned currents (FACs) is located at ±75° magnetic latitude while the location of the second region of the FACs is at ±65°. The values of FACs were adjusted so that the polar cup potential difference was in agreement to statistical model Oliver et al. (1983) for the quiet geomagnetic conditions (Kp 2). For the solar EUV flux, we have used the technique of Nusinov (1984) to construct the flux spectra for the period under study. For the electron precipitations, we draw up several precipitation zones. At both hemispheres, we have an auroral oval electron flux precipitation with a characteristic energy of 3 keV and with a maximal flux of 4 erg/(cm s) at 00 MLT. Further we have the soft electron flux in the cusp region of 0.2 keV, energy flux of 0.2 erg/(cm s) (Aparicio et al., 1991). and the diffusive precipitation in the nighttime sector with 0.1 keV electrons, energy flux of 0.1 erg/ (cm s) (Galperin et al.,1977). The spectral characteristic of the soft and energetic precipitating electrons was chosen according to the Maxwellian energy distribution. The spatial distribution has Gaussian form in both longitudinal and latitudinal direction. The adopted auroral precipitating energy flux and spatial distribution are typical for lower geomagnetic conditions and according to statistical model Hardy et al. (1985). The lower boundary conditions for the neutral gas temperature and densities were predefined and depend only on the geomagnetic latitude. Neutral temperature ranges from 228 K in the winter hemisphere to 164 K in summer. The neutral densities values of N2, O2 and O are minimal at the southern pole (2 1014 cm 3 for N2 and 5 1013 cm 3 for O2) and increase linearly to
the maximum at southern hemisphere (3 1014 cm 3, 7 1013 cm 3 for N2 and O2, respectively (Koshelev et al., 1983). Another input model parameters have been described in detail by Korenkov et al., 1998. It may be note here that all input parameters are based on accumulated experimental data and represent average values for the geophysical condition under study. These input data cannot vary within wide limits for the given conditions. The model GSM TIP may be used in a ‘‘weather” mode with emphasis on August time-dependent input data. But it was also run in a ‘‘climatological” mode in order to specify the baseline conditions. Under these circumstances, there was a little day to day variation in the model calculation and it was possible to simulate just one day as being representative of the whole month, with no adjustments made to the input parameters to obtained better agreement with IRI or experimental data. We calculated the global ionosphere parameters distributions using GSM TIP model for the 10 August, 1999 and compared this results with IRI model results obtained for the same conditions. We chouse this day because it was very quiet geomagnetic day and located about middle of the month. So, the variation of the solar zenith angle during the month not very important for our calculations. The solar activity for the period under study is generally characterized by moderate values of the F10.7 around 130. We can say that during a week over this day solar activity was no greater than 140 and some days even less than 130, although average value F10.7 P for the month was really greater than 140. The observed Kp indices for this period are equal 9, so choused day was characterized quiet geomagnetic conditions. The results of comparison of ionospheric parameters between IRI model and theoretical model GSM TIP are presented in Figs. 1–6. The global difference fields of the Ne, Ti, Te, foF2 and TEC are presented in geographic Cartesian coordinate system for 00 UT. The position of the subsolar point is shown by a circle. The contours of the difference fields for the Te,i calculated with using formula DX = X(GSM TIP) X(IRI)/X(IRI) in %, where X is Te,i and X(GSM TIP) X(IRI) for foF2. For concentration and TEC was used formula DY = Y(GSM TIP)/ Y(IRI) where Y is Ne or TEC respectively. Beside that in Fig. 6 we presented diurnal plots of F2-layer critical frequencies at two mid-latitude stations Kaliningrad (54°N, 20°E) and Sophia (42.5°N, 23.4°E), which were obtained as with using GSM TIP model both with IRI. 4. Discussion and conclusion As we can see from figures that the largest disagreements between IRI and GSM TIP model results are observed at high-latitude ionosphere for Ne at 110 km altitude (Fig. 1) and for foF2 as in polar ionosphere both equatorial region (Fig. 2). Discrepancies between models for foF2 in the high latitudes are primarily due to the fact that IRI model has inadequate specification of the spatial distribu-
Y.N. Korenkov et al. / Advances in Space Research 43 (2009) 1633–1637
(Te(GSM TIP) - Te(IRI))/Te(IRI), % h=300 km 00:00 UT
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Fig. 1. Global distribution of the ratio of the Ne (GSM TIP) and Ne (IRI) at the 110 km altitude for 00 UT.
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Longitude (deg) Fig. 2. Global distribution for 00 UT of the absolute differences of the foF2 (GSM TIP) and foF2 (IRI) MHz.
tion of the electron precipitation zones and effects of the electromagnetic plasma drifts, that taking into account in the GSM TIP model and do not include in the IRI model. Disagreements between models for the foF2 in the equatorial latitudes especially near latitude 0° and longitude 270° may be connected with inadequate spatial distribution and values of the dynamo electric field, which self-consistently calculates in the GSM TIP model. These electric fields reproduce unrealistic the well-known double peak of the Appleton Anomaly in the GSM TIP model, which more realistic reproduces in the IRI model. Some characteristics of global maps for the Ti,e (in percent) at the 300 km altitude (Fig. 3 and 4) are as follows. The most of differences between GSM TIP values of Ti and those computed from IRI model are to be found within the boundaries of ±10%, and in the southern hemisphere in the night-time sector Ti from IRI larger then Ti from GSM TIP more then 18% (Fig. 3). The spatial distribution of the differences for the DTe (Fig. 4) is more complicated than for
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Fig. 6. Diurnal UT-variations of the foF2 calculated from GSM TIP (solid lines), from IRI (CCIR coefficients – dotted lines; URSI coefficients – dashed lines) and experimental data (full circles) for Kaliningrad station (top) and Sophia (bottom).
DTi and characterizes by considerable variations as latitude both longitude directions. The GSM TIP model predominantly underestimates the Te value with respect to IRI, except in the small polar region in the southern hemisphere. The greatest discrepancies between Te calculated from GSM TIP and IRI (>30%) are observed in longitude region during times from 06 to 12 h LT and at all latitudes. These large differences may be connected with inadequate representation of the spatial distribution of the Te in the IRI model, which has very inhomogeneous spatial structure. It may be occurred as a consequence of the limitation experimental data about Te at the 300 km altitude. Fig. 5 shows global distribution of ratio of the TEC calculated with using GSM TIP model to TEC obtained from IRI. At high latitudes of the northern hemisphere TEC from GSM TIP model is lager then IRI TEC by a factor of 2.5 and vice versa in the southern hemisphere IRI TEC is greater GSM TIP TEC except a narrow region at the sub-polar ionosphere that may be connected with electron precipitations. In the others regions the ratio of two TEC is located within the boundaries of factor 2. As seen from the results presented above the quantitative differences between various ionospheric parameters
are observed as at the F2-layer altitudes both at the upper ionosphere. Some of them are connected with features of the electron precipitations at the high latitudes (e.g. DNe at 110 km) another differences may be associated with the effects of E B drift and neutral wind, which are not input parameters and calculated self-consistent in GSM TIP model. It may be noted here that equation for the potential of electric field in this version of our model is solved in the geomagnetic spherical coordinate system. This is unsuitable around equator and introduces errors into electric field distribution and electron concentration as well. Fig. 6 shows diurnal UT-variations of the foF2 for the two mid-latitude stations (Kaliningrad and Sophia) with comparison IRI data and observed data for the Kaliningrad station at the period under study. The experimental data for diurnal variation of the foF2 on Fig. 6 represent possible deviation real data vs. modeled values of these parameters. As seen from figure, agreement between GSM TIP model foF2, IRI data and measured data is reasonable well except morning sector. In our model in morning time Ne increases more rapidly then in the IRI model, but the IRI model overestimate the foF2 experimental morning peak data. For Sophia station, it is seen from figure the diurnal behavior of foF2 for two models are similar to variations for Kaliningrad station and in general agreement between model results and experimental data is reasonable good. For the IRI calculations we used either the URSI or CCIR coefficients. The deviations between two versions of the coefficients are generally less than 1 MHz and IRI with CCIR gives lower values of foF2 than IRI with URSI coefficients. So, analysis of the presented results makes it possible to draw the following conclusions. In the presented paper we made a global comparison of the some ionosphere parameters (Ne, Ti,e, foF2, TEC) obtained with using theoretical self-consistent model GSM TIP and empirical IRI model. From the comparison of these two different models it was realized that large discrepancies between GSM TIP model ionosphere data and IRI model data may be found, especially in the high and low-latitudes regions. The results obtained in this study can be useful for the future improving both models. These modifications may be concerned with incorporate a new experimental data into IRI at the high-latitude regions and more adequate spatial distribution for the Ti and Te. In this study we used GSM TIP model without special fitting of the initial and boundary conditions and others input model parameters. The more precise absolute-value predictions, however, requires some adjustment to bring the calculated values into agreement with data-based IRI model. Besides that, current efforts are focusing on the modification of numerical calculation scheme of the electric field in the GSM TIP model for improving global representation ionosphere parameters. This will permit to obtain more adequate global distributions of the ionosphere parameters in theoretical.
Y.N. Korenkov et al. / Advances in Space Research 43 (2009) 1633–1637
References Aparicio, B., Thelin, B., Lundin, R. The polar cusp from a particle point of view: a statistical study based on Viking data. J. Geophys. Res. 96, 14023–14031, 1991. Bilitza, D. International reference ionosphere 2000. Radio Sci. 36, 261– 275, 2001. Fesen, C.G., Hysell, D.L., Meriwether, J.M., Mendillo, M., et al. Modeling of low-latitude thermosphere and ionosphere. J. Atmos. Solar-Terr. Phys. 64, 1337–1349, 2002. Galperin, Y.I., Crasnier, J., Lissakov, Yu.V., Nicholaenko, L.M., Sinitsin, V.M., Sauvand, J.-A., Khalipov, V.L. Diffuse auroral zone I. Model of the equatorial border of the auroral electron diffuse precipitation zone in the evening and near-midnight sectors (in Russian). Cosmic. Res. 15, 421–434, 1977. Hardy, D.A., Gussenhoven, J., Brautigam, D. A statistical model of auroral electron precipitation. J. Geophys. Res. 90, 4229–4248, 1985. Korenkov, Yu.N., Klimenko, V.V., Forster, M., Surotkin, V.A., Smilauer, J. Global modeling study (GSM TIP) of the ionospheric effects of excited N2, convection and heat fluxes by comparison with EISCAT and satellite data for 31 July 1990. Ann. Geophys. 14, 1362–1374, 1996. Korenkov, Yu.N., Klimenko, V.V., Forster, M., Bessarab, F.S., Surotkin, V.A. Calculated and observed ionospheric parameters for Magion2passage above EISCAT on July 31 1990. J. Geophys. Res. 103, 14697–14710, 1998. Koshelev, V.V., Klimov, N.M., Suturin, N.A. Aeronomy of the mesosphere and lower thermosphere (in Russian). Nauka, Moscow, p. 182, 1983.
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Meza, A.M., Diaz, A.R., Brunini, C.A., Van Zele, M.A. Systematic behavior of semi-empirical global ionospheric models in quiet geomagnetic conditionsm Radio Sci. 37, doi: 10.1029/2001RS002482, 2002. Namgaladze, A.A., Korenkov, Yu.N., Klimenko, V.V., Karpov, I.V., Bessarab, F.S., et al. Global model of the thermosphere–ionosphere– protonosphere system. Pure Appl. Geophys. 127, 219–254, 1988. Namgaladze, A.A., Korenkov, Yu.N., Klimenko, V.V., Karpov, I.V., et al. Numerical modeling of the thermosphere–ionosphere–protonosphere system. J. Atmos.-Terr. Phys. 53, 1113–1124, 1991. Nusinov, A.A. Dependence of intensity of lines of shortwave radiation of the Sun on activity level (in Russian). Geomagn. Aeron. 24, 529–536, 1984. Oliver, W.L., Holt, J.M., Wand, R.H., Evans, J.V. Millstone Hill incoherent scatter observation of auroral convection over 60° 6 K 6 75°. 3. Average patterns versus Kp. J. Geophys. Res. 88, 5505–5516, 1983. Schunk, R.W. A mathematical model of the middle and high-latitude ionosphere. Pure Appl. Geophys. 127, 253–303, 1988. Szuszczewicz, E.P., Fejer, B., Roelof, E., Schunk, R.W., et al. Modeling and measurements of global-scale ionospheric behavior under solar minimum, equinoctial conditions. Adv. Space Res. 12, 105–115, 1992. Szuszczewicz, E.P., Torr, D., Wilkinson, P., Richards, P., Roble, R., Emery, B.A., et al. F region climatology during the Sundial/Atlas 1 campaign of March 1996: model measurements comparisons and cause–effect relationships. J. Geophys. Res. 101, 16758–26741, 1996.
Advances in Space Research 43 (2009) 1633–1637 www.elsevier.com/locate/asr
Global comparison of the model results of GSM TIP with IRI for summer conditions Yu N. Korenkov *, V.V. Klimenko, F.S. Bessarab WD IZMIRAN, Pobedy av., 41, 236017 Kaliningrad, Russia Received 21 November 2007; received in revised form 7 August 2008; accepted 7 August 2008
Abstract This paper presents the results of the numerical calculations thermosphere/ionosphere parameters which were executed with using of the Global Self-consistent Model of the Thermosphere, Ionosphere and Protonosphere (GSM TIP)and comparison of these results with empirically-based model IRI-2001. Model GSM TIP was developed in West Department of IZMIRAN and solves self-consistently the time-dependent, 3-D coupled equations of the momentum, energy and continuity for neutral particles (O2, N2, O), ions (O+, H+), molecular ions (M+) and electrons and largescale eletric field of the dynamo and magnetospheric origin in the range of height from 80 km to 15 Earth’s radii. The empirically derived IRI model describes the E and F regions of the ionosphere in terms of location, time, solar activity and season. Its output provides a global specification not only of Ne but also on the ion and electron temperatures and the ion composition. These two models represent a unique set of capabilities that reflect major differences in along with a substantial approaches of the first-principles model and global database model for the mapping ionosphere parameters. We focus on global distribution of the Ne, Ti, Te and TEC for the one moment UT and fixed altitudes: 110 km, hmF2, 300 km and 1000 km. The calculations were executed with using of GSM TIP and IRI models for August 1999, moderate solar activity and quiet geomagnetic conditions. Results present as the global differences between the IRI and GSM TIP models predictions. The discrepancies between model results are discussed. Ó 2009 Published by Elsevier Ltd on behalf of COSPAR. Keywords: Ionospheric parameters; Theoretical model; IRI; Global comparison
1. Introduction The main physical principles of the terrestrial ionosphere are reasonably well understood and are described by a set of appropriate equations of plasma hydrodynamics (Schunk, 1988). Investigations of the ionospheric processes by solving the first principles equations have some degree of success as shown by comparisons of the model results with observations and empirical ionospheric model (e.g. IRI). The discrepancies between theoretical and empirical models outputs are frequently attributed inadequate constrains on the model inputs or to mathematical simplifications of some physical processes. Hence, the capabilities of an individual theoretical model to describe adequately the *
Corresponding author. E-mail address: [email protected] (Y.N. Korenkov).
0273-1177/$36.00 Ó 2009 Published by Elsevier Ltd on behalf of COSPAR. doi:10.1016/j.asr.2008.08.016
experimental data are a good test of the validity of the mathematical model. Efforts to validate ionospheric models and to do comparisons between them have been initiated by many authors (e.g. Szuszczewicz et al., 1992, 1996; Meza et al., 2002; Fesen et al., 2002). In this paper, we make use of the first principle global model GSM TIP, developed in WD IZMIRAN, Kaliningrad, to simulate global distributions of the ionospheric parameters for August 1999, geomagnetic quiet condition and comparison of the model output with empirical IRI model (Bilitza, 2001). 2. Brief GSM TIP description The global self-consistent model of the thermosphere, ionosphere and protonosphere was developed in the West Department of IZMIRAN of the Russian Academy of Sci-
1634
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ence. For given input data the model calculates the timedependent global three-dimensional structure of the temperature, composition (O2, N2, O), and vector velocity of the neutral atmosphere and of the densities, temperatures, and vector velocities of atomic (O+, H+) and molecular ions and two-dimensional distribution of the electric field potential both of dynamo and magnetospheric origin. The solution is performed numerically on a global grid with resolutions of 5° in latitude and 15° in longitude in spherical geomagnetic coordinate system. In the vertical dimension, the thermospheric code uses 30 grid points between 80 and 520 km altitude above the Earth’s surface. The ionospheric part of the code (F2 region and upper ionosphere) has variable spatial steps along the magnetic field lines from a base altitude of 175 km to a maximum distance of 15 Earth radii. Note here that ionospheric code is not necessary upper boundary conditions. Model inputs are: (1) the solar UV and EUV spectra, (2) the precipitating electron fluxes, and (3) the distribution of the field-aligned currents in the first and second high-latitude region. The model has been described in detail by Namgaladze et al. (1988, 1991) and its application has been presented in the papers (Korenkov et al.,1996, 1998). 3. Input data and results In our model the first region of the field-aligned currents (FACs) is located at ±75° magnetic latitude while the location of the second region of the FACs is at ±65°. The values of FACs were adjusted so that the polar cup potential difference was in agreement to statistical model Oliver et al. (1983) for the quiet geomagnetic conditions (Kp 2). For the solar EUV flux, we have used the technique of Nusinov (1984) to construct the flux spectra for the period under study. For the electron precipitations, we draw up several precipitation zones. At both hemispheres, we have an auroral oval electron flux precipitation with a characteristic energy of 3 keV and with a maximal flux of 4 erg/(cm s) at 00 MLT. Further we have the soft electron flux in the cusp region of 0.2 keV, energy flux of 0.2 erg/(cm s) (Aparicio et al., 1991). and the diffusive precipitation in the nighttime sector with 0.1 keV electrons, energy flux of 0.1 erg/ (cm s) (Galperin et al.,1977). The spectral characteristic of the soft and energetic precipitating electrons was chosen according to the Maxwellian energy distribution. The spatial distribution has Gaussian form in both longitudinal and latitudinal direction. The adopted auroral precipitating energy flux and spatial distribution are typical for lower geomagnetic conditions and according to statistical model Hardy et al. (1985). The lower boundary conditions for the neutral gas temperature and densities were predefined and depend only on the geomagnetic latitude. Neutral temperature ranges from 228 K in the winter hemisphere to 164 K in summer. The neutral densities values of N2, O2 and O are minimal at the southern pole (2 1014 cm 3 for N2 and 5 1013 cm 3 for O2) and increase linearly to
the maximum at southern hemisphere (3 1014 cm 3, 7 1013 cm 3 for N2 and O2, respectively (Koshelev et al., 1983). Another input model parameters have been described in detail by Korenkov et al., 1998. It may be note here that all input parameters are based on accumulated experimental data and represent average values for the geophysical condition under study. These input data cannot vary within wide limits for the given conditions. The model GSM TIP may be used in a ‘‘weather” mode with emphasis on August time-dependent input data. But it was also run in a ‘‘climatological” mode in order to specify the baseline conditions. Under these circumstances, there was a little day to day variation in the model calculation and it was possible to simulate just one day as being representative of the whole month, with no adjustments made to the input parameters to obtained better agreement with IRI or experimental data. We calculated the global ionosphere parameters distributions using GSM TIP model for the 10 August, 1999 and compared this results with IRI model results obtained for the same conditions. We chouse this day because it was very quiet geomagnetic day and located about middle of the month. So, the variation of the solar zenith angle during the month not very important for our calculations. The solar activity for the period under study is generally characterized by moderate values of the F10.7 around 130. We can say that during a week over this day solar activity was no greater than 140 and some days even less than 130, although average value F10.7 P for the month was really greater than 140. The observed Kp indices for this period are equal 9, so choused day was characterized quiet geomagnetic conditions. The results of comparison of ionospheric parameters between IRI model and theoretical model GSM TIP are presented in Figs. 1–6. The global difference fields of the Ne, Ti, Te, foF2 and TEC are presented in geographic Cartesian coordinate system for 00 UT. The position of the subsolar point is shown by a circle. The contours of the difference fields for the Te,i calculated with using formula DX = X(GSM TIP) X(IRI)/X(IRI) in %, where X is Te,i and X(GSM TIP) X(IRI) for foF2. For concentration and TEC was used formula DY = Y(GSM TIP)/ Y(IRI) where Y is Ne or TEC respectively. Beside that in Fig. 6 we presented diurnal plots of F2-layer critical frequencies at two mid-latitude stations Kaliningrad (54°N, 20°E) and Sophia (42.5°N, 23.4°E), which were obtained as with using GSM TIP model both with IRI. 4. Discussion and conclusion As we can see from figures that the largest disagreements between IRI and GSM TIP model results are observed at high-latitude ionosphere for Ne at 110 km altitude (Fig. 1) and for foF2 as in polar ionosphere both equatorial region (Fig. 2). Discrepancies between models for foF2 in the high latitudes are primarily due to the fact that IRI model has inadequate specification of the spatial distribu-
Y.N. Korenkov et al. / Advances in Space Research 43 (2009) 1633–1637
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Fig. 1. Global distribution of the ratio of the Ne (GSM TIP) and Ne (IRI) at the 110 km altitude for 00 UT.
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tion of the electron precipitation zones and effects of the electromagnetic plasma drifts, that taking into account in the GSM TIP model and do not include in the IRI model. Disagreements between models for the foF2 in the equatorial latitudes especially near latitude 0° and longitude 270° may be connected with inadequate spatial distribution and values of the dynamo electric field, which self-consistently calculates in the GSM TIP model. These electric fields reproduce unrealistic the well-known double peak of the Appleton Anomaly in the GSM TIP model, which more realistic reproduces in the IRI model. Some characteristics of global maps for the Ti,e (in percent) at the 300 km altitude (Fig. 3 and 4) are as follows. The most of differences between GSM TIP values of Ti and those computed from IRI model are to be found within the boundaries of ±10%, and in the southern hemisphere in the night-time sector Ti from IRI larger then Ti from GSM TIP more then 18% (Fig. 3). The spatial distribution of the differences for the DTe (Fig. 4) is more complicated than for
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Longitude (deg) Fig. 5. Global distribution for 00 UT of the ratio of the TEC (GSM TIP) and TEC (IRI) at the 1000 km altitude.
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Fig. 6. Diurnal UT-variations of the foF2 calculated from GSM TIP (solid lines), from IRI (CCIR coefficients – dotted lines; URSI coefficients – dashed lines) and experimental data (full circles) for Kaliningrad station (top) and Sophia (bottom).
DTi and characterizes by considerable variations as latitude both longitude directions. The GSM TIP model predominantly underestimates the Te value with respect to IRI, except in the small polar region in the southern hemisphere. The greatest discrepancies between Te calculated from GSM TIP and IRI (>30%) are observed in longitude region during times from 06 to 12 h LT and at all latitudes. These large differences may be connected with inadequate representation of the spatial distribution of the Te in the IRI model, which has very inhomogeneous spatial structure. It may be occurred as a consequence of the limitation experimental data about Te at the 300 km altitude. Fig. 5 shows global distribution of ratio of the TEC calculated with using GSM TIP model to TEC obtained from IRI. At high latitudes of the northern hemisphere TEC from GSM TIP model is lager then IRI TEC by a factor of 2.5 and vice versa in the southern hemisphere IRI TEC is greater GSM TIP TEC except a narrow region at the sub-polar ionosphere that may be connected with electron precipitations. In the others regions the ratio of two TEC is located within the boundaries of factor 2. As seen from the results presented above the quantitative differences between various ionospheric parameters
are observed as at the F2-layer altitudes both at the upper ionosphere. Some of them are connected with features of the electron precipitations at the high latitudes (e.g. DNe at 110 km) another differences may be associated with the effects of E B drift and neutral wind, which are not input parameters and calculated self-consistent in GSM TIP model. It may be noted here that equation for the potential of electric field in this version of our model is solved in the geomagnetic spherical coordinate system. This is unsuitable around equator and introduces errors into electric field distribution and electron concentration as well. Fig. 6 shows diurnal UT-variations of the foF2 for the two mid-latitude stations (Kaliningrad and Sophia) with comparison IRI data and observed data for the Kaliningrad station at the period under study. The experimental data for diurnal variation of the foF2 on Fig. 6 represent possible deviation real data vs. modeled values of these parameters. As seen from figure, agreement between GSM TIP model foF2, IRI data and measured data is reasonable well except morning sector. In our model in morning time Ne increases more rapidly then in the IRI model, but the IRI model overestimate the foF2 experimental morning peak data. For Sophia station, it is seen from figure the diurnal behavior of foF2 for two models are similar to variations for Kaliningrad station and in general agreement between model results and experimental data is reasonable good. For the IRI calculations we used either the URSI or CCIR coefficients. The deviations between two versions of the coefficients are generally less than 1 MHz and IRI with CCIR gives lower values of foF2 than IRI with URSI coefficients. So, analysis of the presented results makes it possible to draw the following conclusions. In the presented paper we made a global comparison of the some ionosphere parameters (Ne, Ti,e, foF2, TEC) obtained with using theoretical self-consistent model GSM TIP and empirical IRI model. From the comparison of these two different models it was realized that large discrepancies between GSM TIP model ionosphere data and IRI model data may be found, especially in the high and low-latitudes regions. The results obtained in this study can be useful for the future improving both models. These modifications may be concerned with incorporate a new experimental data into IRI at the high-latitude regions and more adequate spatial distribution for the Ti and Te. In this study we used GSM TIP model without special fitting of the initial and boundary conditions and others input model parameters. The more precise absolute-value predictions, however, requires some adjustment to bring the calculated values into agreement with data-based IRI model. Besides that, current efforts are focusing on the modification of numerical calculation scheme of the electric field in the GSM TIP model for improving global representation ionosphere parameters. This will permit to obtain more adequate global distributions of the ionosphere parameters in theoretical.
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