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Statistical analysis of ionospheric mid-latitude trough over the Northern Hemisphere derived from GPS total electron content data
© Yang et al. 2015
- Received: 20 August 2015
- Accepted: 27 November 2015
- Published: 8 December 2015
This study statistically investigated the seasonal variation, magnetic local time (MLT) variation, geomagnetic activity dependence, and solar activity dependence of the mid-latitude trough using GPS total electron content (TEC) data from 2000 to 2014. The daily median Kp index was used to characterize the daily geomagnetic activity level. The results showed that the trough minimum position depended primarily on the geomagnetic activity, MLT, and the season. The trough depth depended primarily on the solar flux index (F107) and, to a lesser degree, on MLT. The trough depth increased as F107 increased and as the incidence angle of solar flux decreased. The trough equatorward half-width decreased as the geomagnetic activity increased. These variations in the GPS-TEC trough minimum position were compared with the variations in the TEC trough derived from the International Reference Ionosphere (IRI)-2007 model. The GPS-TEC trough minimum position changed little with respect to F107, whereas the IRI-TEC trough minimum position showed a strong F107 dependence.
- Mid-latitude trough
- Statistic analysis
- Geomagnetic activity variation
- Solar activity variation
The ionospheric mid-latitude trough is a depleted region of ionospheric plasma density in the nightside F region and lies just equatorward of the auroral equatorward boundary. Throughout the paper, trough will refer specifically to the mid-latitude trough. The trough generally consists of three parts: an equatorward wall, a trough minimum, and a poleward wall. Because the large electron density gradient on either side of the trough affects radio wave propagation, the precise position of the trough is very important for many practical activities, such as trans-ionospheric communication and navigation.
Since Muldrew (1965) discovered the trough with a topside sounder, the formation and maintenance mechanisms of the trough have been studied extensively, but many properties of the trough remain incompletely understood. Several mechanisms have been proposed to explain the trough in the pre-midnight sector. The first mechanism is plasma stagnation and decay of ionization in darkness in a region where corotation and convection electric fields counteract each other (e.g., Knudsen 1974; Spiro et al. 1978; Collis and Häggström 1988; and Hedin et al. 2000). Another mechanism for the trough formation during periods of enhanced geomagnetic activity is related to large poleward electric field events, which are also called subauroral ion drifts (SAIDs). The enhanced electric field can cause depletions in electron concentration by enhancing the recombination rate (Schunk et al. 1976). In addition, westward plasma drift driven by the large poleward electric field also advects depleted plasma density to earlier magnetic times; as such, the high-density plasma in earlier magnetic times can be displaced by the depleted plasma density. Rodger et al. (1992) pointed out that the trough is the “normal” ionosphere between the poleward wall and the equatorward wall. The poleward wall is formed by precipitation or plasma transported from elsewhere (Rodger et al. 1986), and the equatorward wall is formed by corotating plasma that continues to decay with time and replenishment from the plasmasphere, but the maintenance mechanism is absent in the vicinity of the trough. Evans et al. (1983) pointed out that the trough formed in the dusk-side region may be a fossil corotating into the nightside sector toward dawn. It is worthy to note that a specific mechanism alone cannot account for density depletion, because the F region plasma is long-lived and a particular mechanism may not be at work throughout the observation period (Nilsson et al. 2005).
The trough has been investigated using various data and methods such as data from satellites, tomography, total electron content (TEC), incoherent scatter radar (ISR), and models (Muldrew 1965; Nilsson et al. 2005; Pryse et al. 2006; Middleton et al. 2008; He et al. 2011; Lee et al. 2011; Ishida et al. 2014). Currently, due to the fast-growing number of ground-based GPS receivers, GPS-TEC measurements have been increasingly used for upper atmospheric research. Horvath and Essex (2003) used TEC measurements from three stations to investigate the features of the Southern Hemisphere trough. Wielgosz et al. (2004) showed that the structure of the ionosphere trough can be regularly identified from latitudinal GPS-TEC plots. In addition, Krankowski et al. (2008) and Zou et al. (2011) utilized GPS-TEC data to study the trough over Europe and Alaska, respectively. These studies demonstrated that GPS-TEC can be used to routinely identify the ionosphere trough.
The GPS-TEC data used in this study were downloaded from MIT Haystack’s Madrigal database mirror site at the Institute of Geology and Geophysics, Chinese Academy Sciences (http://madrigal.iggcas.ac.cn/madrigal/). There are more than 2000 GPS receivers distributed across the globe. MIT Haystack has automated the process of downloading and processing GPS data (Rideout and Coster 2006) to produce globally gridded TEC data with a resolution of 5 min. The geomagnetic activity index Kp and solar flux index F107 data were downloaded from the National Geophysical Data Center (ftp://ftp.ngdc.noaa.gov/STP/GEOMAGNETIC_DATA/INDICES/KP_AP/). In this study, we primarily investigated the trough structure averaged longitudinally over a day. As such, the daily median Kp index was used to characterize the daily geomagnetic activity level. In order to study the seasonal variation of the mid-latitude trough, the data were divided into three seasons: summer (May–July), equinox (February–April, August–October), and winter (November–January).
The TEC maps were used to create latitudinal TEC profiles (between 45° and 70° N) with intervals of 2 h and 1° steps in latitude. At first, the trough signature in the latitudinal TEC profile was recognized visually. Then, an automated procedure was used to estimate the trough parameters that formed the dataset used in this study. Although visual identification always involves some subjective judgment, the larger data sample was expected to smooth out such deficiencies.
The trough minimum position depends primarily on geomagnetic activity, MLT, and the season. The trough shifts toward low latitudes with increasing geomagnetic activity and MLT. The seasonal variation in trough minimum position differs strongly with different MLTs.
The trough depth depends primarily on F107 and, to a lesser degree, on MLT. The trough depth increases with increasing F107 and with decreasing incidence angle of solar flux.
The trough equatorward half-width decreases with increasing geomagnetic activity.
The diurnal variation in the IRI-TEC trough minimum position is similar to that of the GPS-TEC trough minimum position. The GPS-TEC trough minimum position changes little with F107, whereas the IRI-TEC trough minimum position shows a strong F107 dependence.
In this study, we examined the trough structure averaged longitudinally over the course of a day. The longitudinal average of the trough structure depends not only on the longitude effect of the trough occurrence rate (He et al. 2011) but also on the longitude effect of the trough structure (Karpachev 2003). The occurrence rate of the trough shows significant variations depending on the season, solar activity, and MLT (Ishida et al. 2014). The longitude effect of the trough minimum position primarily depends on the Kp (Karpachev et al. 1996). These factors can lead to the large scatter of the data and make the interpretation of the data in terms of physical processes more difficult. Although these limitations exist, our results are consistent with those found in many earlier studies. During disturbed conditions, the temperature associated with the disturbed electric field increases in the trough region, and the plasma density at a trough minimum decreases. However, in this study, the TEC at the trough minimum remained constant with increasing Kp. Pryse et al. (2006) investigated the TEC trough in the United Kingdom and found the same feature. Therefore, the relationship between the TEC value at the trough minimum and the temperature at the trough minimum is needed to study at different geomagnetic activities, which can help us understand the physical mechanism of trough formation. In addition, a quantitative test of the wind effect in the trough is also needed in the future.
The mid-latitude trough is a typical feature of the F region. It has been demonstrated that GPS-TEC data can be used to investigate the time and space evolution of the trough, although the data provide no altitudinal information.
This research was supported by the Chinese Academy of Sciences project (KZZD-EW-01-3), National Key Basic Research Program of China (2012CB825604), and National Natural Science Foundation of China (41374162, 41231065, and 41321003). The GPS-TEC data used in this study were downloaded from MIT Haystack’s Madrigal database mirror site at the Institute of Geology and Geophysics, Chinese Academy Sciences (http://madrigal.iggcas.ac.cn/madrigal/).
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- Balan N, Bailey GJ, Su YZ (1996) Variations of the ionosphere and related solar fluxes during solar cycles 21 and 22. Adv Space Res 18(3):11–14View ArticleGoogle Scholar
- Collis PN, Häggström I (1988) Plasma convection and auroral precipitation processes associated with the main ionospheric trough at high latitudes. J Atmos Terr Phys 50:389–404View ArticleGoogle Scholar
- Doe RF, Vickrey JF, Mendillo M (1995) Electrodynamic model for the formation of auroral ionospheric cavities. J Geophys Res 100:9683–9696. doi:10.1029/95JA00001 View ArticleGoogle Scholar
- Emmert JT, Fejer BG, Shepherd GG, Solheim BH (2002) Altitude dependence of middle and low-latitude daytime thermospheric disturbance winds measured by WINDII. J Geophys Res 107(A12):1483. doi:10.1029/2002JA009646 View ArticleGoogle Scholar
- Evans JV, Holt JM, Oliver WL, Wand RH (1983) The fossil theory of nighttime high latitude F region troughs. J Geophys Res 88(A10):7769–7782View ArticleGoogle Scholar
- Fisher DJ, Makela JJ, Meriwether JW, Buriti RA, Benkhaldoun Z, Kaab M, Lagheryeb A (2015) Climatologies of nighttime thermospheric winds and temperatures from Fabry-Perot interferometer measurements: from solar minimum to solar maximum. J Geophys Res Space Physics 120:6679–6693. doi:10.1002/2015JA021170 View ArticleGoogle Scholar
- He M, Liu L, Wan W, Zhao B (2011) A study on the nighttime midlatitude ionospheric trough. J Geophys Res 116:A05315. doi:10.1029/2010JA016252 Google Scholar
- Hedin M, Häggström I, Pellinen-Wannberg A, Andersson L, Brändström U, Gustavsson B, Steen Å, Westman A, Wannberg G, Van Eyken T, Aso T, Cattell C, Carlson CW, Klumpar D (2000) 3-D extent of the main ionospheric trough—a case study. Adv Pol Up Atm Res 14:157–162Google Scholar
- Horvath I, Essex EA (2003) The Southern Hemisphere mid-latitude day-time and nighttime trough at low-sunspot numbers. J Atmos Terr Phys 65:917–940View ArticleGoogle Scholar
- Ishida T, Ogawa Y, Kadokura A, Hiraki Y, Häggström I (2014) Seasonal variation and solar activity dependence of the quiet-time ionospheric trough. J Geophys Res Space Physics 119. doi:10.1002/2014JA019996.
- Karpachev AT (2003) The dependence of the main ionospheric trough shape on longitude, altitude, season, local time, and solar and magnetic activity. Geomagn Aeron 43(2):239–251Google Scholar
- Karpachev AT, Deminov MG, Afonin VV (1996) Model of the mid-latitude ionospheric trough on the base of cosmos-900 and intercosmos-19 satellites data. Adv Space Res 18:6221–6230View ArticleGoogle Scholar
- Knudsen WC (1974) Magnetospheric convection and the high-latitude F2 ionosphere. J Geophys Res 79(7):1046–1055View ArticleGoogle Scholar
- Krankowski A, Shagimuratov II, Ephishov II, Krypiak-Gregorczyk A, Yakimova G (2008) The occurrence of the mid-latitude ionospheric trough in GPS‐TEC measurements. Adv Space Res 43:1721–1731. doi:10.1016/j.asr.2008.05.014 View ArticleGoogle Scholar
- Lee I, Liu JY, Wang W, Chen C, Lin C (2011) The ionospheric mid-latitude trough observed by FORMOSAT‐3/COSMIC during solar minimum. J Geophys Res 116:A06311. doi:10.1029/2010JA015544 Google Scholar
- Liu JY, Chen YI, Lin JS (2003) Statistical investigation of the saturation effect in the ionospheric foF2 versus sunspot, solar radio noise, and solar EUV radiation. J Geophys Res 108(A2):1067. doi:10.1029/2001JA007543 View ArticleGoogle Scholar
- Liu L, Wan W, Ning B, Pirog OM, Kurkin VI (2006) Solar activity variations of the ionospheric peak electron density. J Geophys Res 111:A08304. doi:10.1029/2006JA011598 Google Scholar
- Lyatsky VB, Mal’tsev P (1981) Origin of the mid-latitude trough and of the polar void in the ionospheric density distribution. Geomag Aeronomy 21:127–128Google Scholar
- Mendillo M, Chacko CC (1977) The baselive ionospheric trough. J Geophys Res 82:5129–5137View ArticleGoogle Scholar
- Middleton HR, Pryse SE, Wood AG, Balthazor R (2008) The role of the tongue-of-ionization in the formation of the poleward wall of the main trough in the European post-midnight sector. J Geophys Res 113:A02306. doi:10.1029/2007JA012631 Google Scholar
- Muldrew DB (1965) F-layer ionization troughs deduced from Alouette data. J Geophys Res 70(11):2635–2650View ArticleGoogle Scholar
- Nilsson H, Sergienko TI, Ebihara Y, Yamauchi M (2005) Quiet-time mid-latitude trough: influence of convection field-aligned currents and proton precipitation. Ann Geophys 23:3277–3288View ArticleGoogle Scholar
- Ohtani S, Wing S, Merkin VG, Higuchi T (2014) Solar cycle dependence of night-side field-aligned currents: effects of dayside ionospheric conductivity on the solar wind-magnetosphere-ionosphere coupling. J Geophys Res Space Physics 119:1–13. doi:10.1002/2013JA019410 View ArticleGoogle Scholar
- Pryse SE, Kersley L, Malan D, Bishop GJ (2006) Parameterization of the main ionospheric trough in the European sector. Radio Sci 41:RS5S14. doi:10.1029/2005RS003364 View ArticleGoogle Scholar
- Rideout W, Coster A (2006) Automated GPS processing for global total electron content data. GPS Solut 10(3):219–228. doi:10.1007/s10291-006-0029-5 View ArticleGoogle Scholar
- Rodger A (2008) The mid-latitude trough: revisited, in mid-latitude ionospheric dynamics and disturbances. Geophys Monogr Ser 181:25–33, AGU Washington D.CGoogle Scholar
- Rodger AS, Brace LH, Hoegy WR, Winningham JD (1986) The poleward edge of the mid-latitude trough-its formation, orientation and dynamics. J Atmos Sol Terr Phys 48(8):715–728View ArticleGoogle Scholar
- Rodger AS, Moffett RJ, Quegan S (1992) The role of ion drift in the formation of ionisation troughs in the mid-and high-latitude ionosphere—a review. J Atmos Sol Terr Phys 54(1):1–30View ArticleGoogle Scholar
- Schunk RW, Banks PM, Raitt WJ (1976) Effects of electric fields and other processes upon the nighttime high latitude F layer. J Geophys Res 81:3271View ArticleGoogle Scholar
- Spiro RW, Heelis RA, Hanson WB (1978) Ion convection and the formation of the mid-latitude F region ionization trough. J Geophys Res 83(A9):4255–4264. doi:10.1029/JA083iA09p04255 View ArticleGoogle Scholar
- Wielgosz P, Baran LW, Shagimuratov II, Aleshnikova MV (2004) Latitudinal variations of TEC over Europe obtained from GPS observations. Ann Geophys 22:405–415. doi:10.5194/angeo-22-405-2004 View ArticleGoogle Scholar
- Zou S, Moldwin MB, Coster A, Lyons LR, Nicolls MJ (2011) GPS TEC observations of dynamics of the mid-latitude trough during substorms. Geophys Res Lett 38:L14109. doi:10.1029/2011GL048178 View ArticleGoogle Scholar