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ICON EXPERIMENT AND DATA USED

The ICON (Ionospheric Connection Explorer) satellite

https://icon.ssl.berkeley.edu/

Orbit: altitude - 575km

          inclination - 27 degrees

Instrument: IVM

Data: Ion temperature (RPA - Retarding Potential Analyzer)

LEVEL 2 data ftp://icon-science.ssl.berkeley.edu

Ti (ion temperature): time resolution 1s

Day 295 2019 - Day 157 2020

data selection in this study:

 spring equinox March 2020

  - ±25 days around March 21, 2020

  - ±7.5 degrees around dip equator

  - very low solar activity PF10.7 ≈ 70

(PF10.7 - average of daily F10.7 and 81-day running mean)

 

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ION TEMPERATURE DATA-BASE

Fig. 1. Year-altitude coverage of the data sets include in our data base. The curve at the top shows the solar 10.7 cm radio flux (F10.7 index).

Fig. 1: Year-altitude coverage of the data sets include in our data-base. The curve at the top shows the solar 10.7 cm radio flux (F10.7 index).

Available satellite data (SPDF, Cedar, etc.)
100s data averages - 13,673,200‬‬ points

 

Tab. 1: Details of datasets from individual satellites included in our data-base (RPA - Retarding Potential Analyzer).

 

Fig. 2: Distribution of data versus altitude from all data sets include in our data-base.

 

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ICON IVM DATA AND ANALYSIS

Fig. 3: Local time variation of ICON IVM-A Ti at the dip equator (±7.5) (grey dots represent measured 1s data). Blue circles represent averages in 0.5h MLT (magnetic local time) intervals centered at 0.25, 0.75,..,23.75h). Error bars represent standard deviation. Red circels represent medians in the same bins and magenta lines upper and lower quartiles. The morning peak maximum at 2500K is located at 7.25h MLT from averages and at 6.75h MLT from medians. Note that Ti data between 4 and 5h MLT shows a large scatter (probably due to some external noise, errors etc.).

Fig. 4: The same as Figure 3 but for 100s averages (made from 1s data) to be consistent with 100s data in our data-base. The averages and medians show negligible differences if calculated from 1s or 100s data (Figure 3 vs. Figure 4). The height of the peak (difference between maximum and night Ti values) is about 1700K.

Fig. 5: Comparison of ICON IVM-A Ti data (averages) and IRI-2016 Ti (green line). The comparison shows that IRI does not include the morning peak in Ti. Very high peak in Ti from ICON IVM-A seems to be close to the electron temperature (IRI-2016/TBT-2012 option red line e.g., Bilitza 2017 et al.; Truhlik et al., 2012). 

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Ti DATA-BASE ANALYSIS

Fig. 6: Local time variation of Ti data from our data-base at the dip equator (±7.5) and from altitude interval 530-650km. Included data are from both equinoxes. Color symbols represent different satellites.

Fig. 7: Selected ROCSAT-1 Ti data from Figure 6. Data represents high solar activity (average PF10.7=160). The height of the peak is about 600K.

Fig. 8: Selected SROSS-C2 Ti data from Figure 6. Data represents low solar activity (average PF10.7=82). The height of the peak is about 1100K.

Fig. 9: Selected C/NOFS Ti data from Figure 6. Data represents medium solar activity (average PF10.7=126). The height of the peak is about 1000K.

Fig. 10: Selected AE-C Ti data from Figure 6 (only cyan dots). Data represents low solar activity (average PF10.7=81). Only a part of the peak captured for equinox. Blue dots include also other seasons. Thus if all seasons are considered AE-C data shows also a pronounced peak (the height about 1400K).

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SOLAR ACTIVITY VARIATION

Fig. 11: Solar activity variation of Ti data included in our data-base (blue +) and ICON IVM-A Ti (red +) for night MLT=0..2h to check consistency of both data-sets. ICON Ti data are slightly above extrapolated linear fit determined from data in the data-base only. The average Ti from ICON data is 732K. Corresponding value from the linear fit is 658K. Thus a correction factor (1/1.1125=658/732) can be introduced.

Fig. 12: Solar activity variation of Ti data at morning peak (MLT=6.5-7.5h) included in our data-base (grey circles) and ICON IVM-A Ti (red circcles and green circles - green show corrected data i.e, original data multiplied by the 1/1.1125 factor). The solar activity variation at the morning peak thus shows a non linear dependence decresing from low to high solar activity.

OPEN

Conclusions

  • We presented a comparison of the ion temperature (Ti) at morning hours from newly available ICON IVM and from other satellite Ti data stored in our data-base.
  • The ICON measurement showed a distict peak with maximum at 7.25h MLT (Figure 3-5).
  • The comparison with IRI-2016 shows that IRI does not include this Ti enhancement. However, the ICON Ti data are close to IRI Te, which suggests that ions at very low solar activity are much more heated by electrons than cooled by neutral particles at this altitude (≈ 600km).
  • Comparison with data from other experiments included in our database shows generally lower peak height than ICON (Figure 7-10).
  • Check consinstency between Ti from ICON and our data-base at night and the equator when Ti should be almost equal to Tn and to exhibit a linear dependence reveals that ICON Ti might be slightly overestimated. A correction factor 1/1.1125 is suggested (Figure 11).
  • Solar activity variation at the peak maximum shows a non-linear dependence. The absolute value of the Ti gradient with PF10.7 index decreases from low solar activity to hight solar activity (Figure 12).
  • Possible improved model of Ti included in IRI should include this non-linear dependency at the Ti morning peak.

 

  • Acknowledgement

    We are very grateful to the ICON team, icon.ssl.berkeley.edu and William B. Hanson Center for Space Sciences at UT Dallas for availability of the IVM Ti data. We are very grateful to J. Smilauer, M. Hairston, the Cedar service, and P. K. Bhuyan and for providing data from Intercosmos 24, DMSP (F11, F12, F13, F14, and F15), and SROSS C2 satellites, respectively. We are also grateful to Space Physics Data Facility (SPDF) for providing the other satellite Ti data.
    This study was supported by grant LTAUSA17100 by the Ministry of Education, Youth and Sports of the Czech Republic

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Abstract

An accurate description of solar activity variation in thermal plasma parameters including ion temperature (Ti) is an important task for empirical modelling.
The recent ion temperature measurement from IVM-A ICON during very low solar activity (PF10.7 about 70 s.f.u.) shows a very pronounced morning peak over the equator at an altitude of about 600km with its maximum at about 7.25h local time (LT). Maximum of Ti values reaches 3000K. The average height of the peak (difference between peak maximum and nighttime temperature) during spring equinox 2020 was about 1700K (only IVM-A data with the highest quality flag was selected). Thus, the observed peak from IVM-A ICON is significantly higher than what Ti data show in the case of previous experiments. The data from earlier experiments were taken from our data-base which has been systematically built from almost all available satellite thermal plasma parameters measurements including Ti (e.g. Truhlik et al. 2019). From other comparable satellite missions comprised in the data-base, ROCSAT-1 data shows the height of the Ti peak about 600K, Indian SROSS C2 about 1100K, C/NOFS about 1000K (only C/NOFS Ti data for PF10.7>95 were considered) etc..
The solar activity variation of Ti at the peak maximum from all the Ti data (IVM-A ICON data plus data from the data-base) exhibits a decrease with increasing solar activity but the dependence is non-linear. The absolute value of the gradient is highest at lowest solar activity and decreases towards solar maximum (for PF10.7<120 the gradient is about -15K/s.f.u., for PF10.7 between 120 and 200 the gradient is about -3K/s.f.u. and for PF10.7 above 220 the gradient is near zero). In spite of that, it might be needed some calibration factor of the IVM-A Ti data (a preliminary comparison with linearly extrapolated trend of Ti in dependence on PF10.7 from the data from the data-base for nighttime suggests about 12% IVM-A Ti reduction), and thus the gradient at low solar activity can a little bit change, we discuss consequences of this non-linear dependence for future steps in empirical modelling of the ion temperature.

 

V. Truhlik, D. Bilitza, P. G. Richards, D. Kotov, L.Triskova, and M. Sulha, 'Global empirical modeling of ion temperature for the International Reference Ionosphere', Presentation at 2019 COSPAR-IRI Workshop, Nicosia, Cyprus, Sept. 2019.

An accurate description of solar activity variation in thermal plasma parameters including ion temperature (Ti) is an important task for empirical modelling.
The recent ion temperature measurement from IVM-A ICON during very low solar activity (PF10.7 about 70 s.f.u.) shows a very pronounced morning peak over the equator at an altitude of about 600km with its maximum at about 7.25h local time (LT). Maximum of Ti values reaches 3000K. The average height of the peak (difference between peak maximum and nighttime temperature) during spring equinox 2020 was about 1700K (only IVM-A data with the highest quality flag was selected). Thus, the observed peak from IVM-A ICON is significantly higher than what Ti data show in the case of previous experiments. The data from earlier experiments were taken from our data-base which has been systematically built from almost all available satellite thermal plasma parameters measurements including Ti (e.g. Truhlik et al. 2019). From other comparable satellite missions comprised in the data-base, ROCSAT-1 data shows the height of the Ti peak about 600K, Indian SROSS C2 about 1100K, C/NOFS about 1000K (only C/NOFS Ti data for PF10.7>95 were considered) etc..
The solar activity variation of Ti at the peak maximum from all the Ti data (IVM-A ICON data plus data from the data-base) exhibits a decrease with increasing solar activity but the dependence is non-linear. The absolute value of the gradient is highest at lowest solar activity and decreases towards solar maximum (for PF10.7<120 the gradient is about -15K/s.f.u., for PF10.7 between 120 and 200 the gradient is about -3K/s.f.u. and for PF10.7 above 220 the gradient is near zero). In spite of that, it might be needed some calibration factor of the IVM-A Ti data (a preliminary comparison with linearly extrapolated trend of Ti in dependence on PF10.7 from the data from the data-base for nighttime suggests about 12% IVM-A Ti reduction), and thus the gradient at low solar activity can a little bit change, we discuss consequences of this non-linear dependence for future steps in empirical modelling of the ion temperature.

 

V. Truhlik, D. Bilitza, P. G. Richards, D. Kotov, L.Triskova, and M. Sulha, 'Global empirical modeling of ion temperature for the International Reference Ionosphere', Presentation at 2019 COSPAR-IRI Workshop, Nicosia, Cyprus, Sept. 2019.

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