Abstract
The zone of anomalous diurnal variations in foF2, which is characterized by an excess of nighttime foF2 values over daytime ones, has been distinguished in the Southern Hemisphere based on the Intercosmos-19 satellite data. In English literature, this zone is usually defined as the Weddell Sea anomaly (WSA). The anomaly occupies the longitudes of 180°–360° E in the Western Hemisphere and the latitudes of 40°–80° S, and the effect is maximal (up to ∼5 MHz) at longitudes of 255°–315° E and latitudes of 60°–70° S (50°–55° ILAT). The anomaly is observed at all levels of solar activity. The anomaly formation causes have been considered based on calculations and qualitative analysis. For this purpose, the longitudinal variations in the ionospheric and thermospheric parameters in the Southern Hemisphere have been analyzed in detail for near-noon and near-midnight conditions. The analysis shows that the daytime foF2 values are much smaller in the Western Hemisphere than in the Eastern one, and, on the contrary, the nighttime values are much larger, as a result of which the foF2 diurnal variations are anomalous. Such a character of the longitudinal effect mainly depends on the vertical plasma drift under the action of the neutral wind and ionization by solar radiation. Other causes have also been considered: the composition and temperature of the atmosphere, plasma flows from the plasmasphere, electric fields, particle precipitation, and the relationship to the equatorial anomaly and the main ionospheric trough.
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References
Bellchambers, W.H. and Piggott, W.R., Ionospheric Measurements Made at Halley Bay, Nature, 1958, vol. 182, pp. 1596–1597.
Bilitza, D. and Reinisch, B., International Reference Ionosphere 2007: Improvements and New Parameters, Adv. Space Res., 2008, vol. 42, no. 4, pp. 599–609.
Burns, A.G., Zeng, Z., Wang, W., Lei, J., Solomon, S.C., Richmond, A.D., Killeen, T.L., and Kuo, Y.-H., The Behavior of the F2 Peak Ionosphere over the South Pacific at Dusk during Quiet Summer Conditions from COSMIC Data, J. Geophys. Res., 2008, vol. 113, no. A12305; doi:10.1029/2008JA013308.
Burns, A., Solomon, S., Wang, W., Richmond, A., Jee, G., Lin, C., Rocken, C., and Kuo, B., Can the Weddell Sea Anomaly and Related Phenomena be Explained by Conjugate Effects?, Proc. 4th COSMIC Data Users Workshop, Boulder, 2009.
Clilverd, M.A., Smith, A.J., and Thomson, N.R., The Annual Variation in Quiet Time Plasmaspheric Electron Density, Determined from Whistler Mode Group Delays, Planet. Space Sci., 1991, vol. 39, pp. 1059–1067.
Deminov, M.G., Karpachev, A.T., Afonin, V.V., and Annakuliev, S.K., Dynamics of the Midlatitude Trough during Magnetic Storm: Main Phase, Geomagn. Aeron., 1995, vol. 35, no. 6, pp. 69–77.
Drob, D.P., Emmert, J.T., Crowley, G., et al., An Empirical Model of the Earth’s Horizontal Wind Fields: HWM07, J. Geophys. Res., 2008, vol. 113, p. A12304; doi:10.1029/2008JA013668.
Dudeney, J.R. and Piggott, W.R., Antarctic Ionospheric Research, Antarct. Res. Ser. Am. Geophys. Union, 1978, vol. 29, pp. 200–235.
Dungey, J.W., Interplanetary Magnetic Field and the Auroral Zones, Phys. Rev. Lett., 1961, vol. 6, pp. 47–48.
Evans, J.V., A Study of F2 Region Night-Time Vertical Ionization Fluxes at Millstone Hill, Planet. Space Sci., 1975, vol. 23, no. 12, pp. 1611–1619.
He, M., Liu, L., Wan, W., Ning, B., Zhao, B., Wen, J., Yue, X., and Le, H., A Study of the Weddell Sea Anomaly Observed by FORMOSAT-3/COSMIC, J. Geophys. Res., 2009, vol. 114, p. A12309; doi:10.1029/2009JA014175.
Hedin, A.E., Extension of the MSIS Thermosphere Model into the Middle and Lower Atmosphere, J. Geophys. Res., 1991, vol. 96, no. 2, pp. 1159–1172.
Hedin, A.E., Biondi, I.A., and Burnside, R.G., Revised Global Model of Thermospheric Winds Using Satellite and Ground-Based Observations, J. Geophys. Res., 1991, vol. 96, no. 5, pp. 7657–7688.
Horvath, I., A Total Electron Content Space Weather Study of the Nighttime Weddell Sea Anomaly of 1996/1997 Southern Summer with TOPEX/Poseidon Radar Altimetry, J. Geophys. Res., 2006, vol. 111, p. A12317; doi:10.1029/2006JA011679.
Horvath, I. and Essex, E.A., The Weddell Sea Anomaly Observed with the TOPEX Satellite Data, J. Atmos. Sol.-Terr. Phys., 2003, vol. 65, pp. 693–706; doi:10.1016/S1364-6826(03)00083-X.
Horvath, I. and Lovell, B.C., Investigating the Relationships among the South Atlantic Magnetic Anomaly, Southern Nighttime Midlatitude Trough, and Nighttime Weddell Sea Anomaly during Southern Summer, J. Geophys. Res., 2009a, vol. 114, p. A02306; doi:10.1029/2008JA013719.
Horvath, I. and Lovell, B.C., An Investigation of the Northern Hemisphere Midlatitude Nighttime Plasma Density Enhancements and Their Relations to the Midlatitude Nighttime Trough during Summer, J. Geophys. Res., 2009b, vol. 114, p. A08308; doi:10.1029/2009JA014094.
Jee, G., Burns, A.G., Kim, Y.H., and Wang, W., Seasonal and Solar Activity Variations of the Weddell Sea Anomaly Observed in the TOPEX Total Electron Content Measurements, J. Geophys. Res., 2009, vol. 114, p. A04307; doi:10.1029/2008JA013801.
Karpachev, A.T. and Gasilov, N.A., Variations of the Vertical Plasma Drift with Longitude in the Midlatitude Nighttime Summer Ionosphere Deduced from Measurements of hmF2, Geomagn. Aeron., 1998, vol. 38, no. 5, pp. 89–99 [Geomagn. Aeron. (Engl. Transl.), 1998, vol. 38, pp. 617–623].
Karpachev, A.T. and Gasilov, N.A., Zonal and Meridional Wind Components Derived from Intercosmos-19 hmF2 Measurements, Adv. Space Res., 2001, vol. 27, no. 6/7, pp. 1245–1252.
Karpachev, A.T. and Gasilov, N.A., Causes of Longitude-Latitudinal Variations in the Ionospheric F2-Layer Maximum in Summer Nighttime Conditions, Int. J. Geomagn. Aeron., 2006, vol. 6, p. GI2006; doi:10.1029/2005GI000112.
Karpachev, A.T., Deminov, M.G., and Afonin, V.V., Model of the Mid-Latitude Ionospheric Trough on the Base of Cosmos-900 and Intercosmos-19 Satellites Data, Adv. Space Res., 1996, vol. 18, no. 6, pp. 221–230.
Karpachev, A.T., Deminov, M.G., and Afonin, V.V., Two Branches of Day-Time Winter Ionospheric Trough according to Cosmos-900 Data at F2-Layer Heights, Adv. Space Res., 1998, vol. 22, no. 6, pp. 877–882.
Karpachev, A.T., Gasilov, N.A., and Karpachev, O.A., Causes of NmF2 Longitudinal Variations at Mid- and Subauroral Latitudes under Summer Nighttime Conditions, Geomagn. Aeron., 2010, vol. 50, no. 4, pp. 507–513 [Geomagn. Aeron. (Engl. Transl.), 2010, vol. 50, pp. 482–488].
Krinberg, I.A. and Tashchilin, A.V., Ionosfera i plazmosfera (The Ionosphere and Plasmasphere), Moscow: Nauka, 1984.
Lin, C. H., Liu, J.Y., Cheng, C.Z., Chen, C.H., Liu, C.H., Wang, W., Burns, A.G., and Lei, J., Three-Dimensional Ionospheric Electron Density Structure of the Weddell Sea Anomaly, J. Geophys. Res., 2009, vol. 114, p. A02312; doi:10.1029/2008JA013455.
Lisakov, Yu., Jorjio, V., Nikolaenko, N.V., and Ainbund, L.M. Observations of Low Intensity Particle Fluxes Inside the Region of the Ionospheric Main Trough and Their Variability, in Results of the ARCAD 3 Project and of Recent Programs in Magnetospheric and Ionospheric Physics, Toulouse: Cepadues, 1985, pp. 261–274.
Meng, C.I., Diurnal Variations of the Auroral Oval Size, J. Geophys. Res., 1979, vol. 84, pp. 5319–5324.
Moffett, R.J. and Quegan, S., The Mid-Latitude Trough in the Electron Concentration of the Ionospheric F-Layer: A Review of Observations and Modeling, J. Atmos. Terr. Phys., 1983, vol. 45, pp. 315–343; doi:10.1016/S0021-9169(83)80038-5.
Pavlov, A.V. and Pavlova, N.M., Anomalous Nighttime Peaks in Diurnal Variations of NmF2 Close to the Geomagnetic Equator: A Statistical Study, J. Atmos. Sol.-Terr. Phys., 2007, vol. 69, pp. 1871–1883; doi:10.1016/j.jastp.2007. 07.003.
Penndorft, R., The Average Ionospheric Conditions over the Antarctic in Geomagnetism and Aeronomy, Antarct. Res. Ser. Am. Geophys. Union, 1965, vol. 4., pp. 1–45.
Rishbeth, H., Rishbeth, H., Thermospheric Winds and the F-Region: A Review, J. Atmos. Terr. Phys., 1972, vol. 34, no. 1, pp. 1–34.
Sitnov, Yu.S., Shubin, V.N., and Annakuliev, S.K., Rishbeth, H., Approximation of the Electron Density and Altitude at a Maximum of the Daytime Midlatitude Ionospheric F2 Region Using Simple Analytic Formulas, Geomagn. Aeron., 1992, vol. 32, no. 4, pp. 128–130.
Takeda, M. and Yamada, Y., Rishbeth, H., Simulation of Ionospheric Electric Fields and Geomagnetic Field Variation by the Ionospheric Dynamo for Different Solar Activity, Ann. Geophys., 1987, vol. 5, no. 6, pp. 429–433.
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Original Russian Text © A.T. Karpachev, N.A. Gasilov, O.A. Karpachev, 2011, published in Geomagnetizm i Aeronomiya, 2011, Vol. 51, No. 6, pp. 828–840.
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Karpachev, A.T., Gasilov, N.A. & Karpachev, O.A. Morphology and causes of the Weddell Sea anomaly. Geomagn. Aeron. 51, 812–824 (2011). https://doi.org/10.1134/S0016793211050070
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DOI: https://doi.org/10.1134/S0016793211050070