Dusk-midnight Sector Research Articles

Effects of Subauroral Polarization Streams on the Upper Thermospheric Winds During Non-Storm Time.

Intense sunward (westward) plasma flows, named Subauroral Polarization Stream (SAPS), have been known to occur equatorward of the electron auroras for decades, yet their effect on the upper thermosphere has not been well understood. On the one hand, the large velocity of SAPS results in large momentum exchange upon each ion‐neutral collision. On the other hand, the low plasma density associated with SAPS implies a low ion‐neutral collision frequency. We investigate the SAPS effect during non‐storm time by utilizing a Scanning Doppler Imager (SDI) for monitoring the upper thermosphere, SuperDARN radars for SAPS, all‐sky imagers and DMSP Spectrographic Imager for the auroral oval, and GPS receivers for the total electron content. Our observations suggest that SAPS at times drives substantial (>50 m/s) westward winds at subauroral latitudes in the dusk‐midnight sector, but not always. The occurrence of the westward winds varies with AE index, plasma content in the trough, and local time. The latitudinally averaged wind speed varies from 60 to 160 m/s, and is statistically 21% of the plasma. These westward winds also shift to lower latitude with increasing AE and increasing MLT. We do not observe SAPS driving poleward wind surges, neutral temperature enhancements, or acoustic‐gravity waves, likely due to the somewhat weak forcing of SAPS during the non‐storm time.

Radiation Belt Response to Fast Reverse Shock at Geosynchronous Orbit

Abstract Fast reverse shocks (FRSs) cause the magnetosphere to expand, by contrast to the well-known compressions caused by the impact of fast forward shocks (FFS). Usually, FFSs are more geoeffective than FRSs, and consequently the inner magnetosphere dynamic responses to both shock types can be quite different. In this study, we investigate for the first time the radiation belt response to an FRS impact using multi-satellite observations and numerical simulations. Spacecraft on the dayside observed decreases in magnetic field strength and energetic (∼40–475 keV) particle fluxes. Timing analysis shows that the magnetic field signature propagated from the dayside to the nightside magnetosphere. Particles with different energies vary simultaneously at each spacecraft, implying a non-dispersive particle response to the shock. Spacecraft located at lower L-shells did not record any significant signatures. The observations indicate a local time dependence of the response associated with the shock inclination, with the clearest signatures being observed in the dusk–midnight sector. Simulations underestimate the amplitude of the magnetic field variations observed on the nightside. The observed decreases in the electron intensities result from a combination of radial gradient and adiabatic effects. The radial gradients in the spectral index appear to be the dominant contributor to the observed variations of electrons seen on the dayside (near noon and dusk) and on the nightside (near midnight). This study shows that even an FRS can affect the radiation belts significantly and provides an opportunity to understand their dynamic response to a sudden expansion of the magnetosphere.

ПЕЛЕНГОВАНИЕ ВЧ СИГНАЛОВ, РАССЕЯННЫХ ИОНОСФЕРНЫМИ НЕОДНОРОДНОСТЯМИ, С ПОМОЩЬЮ МАЛОРАЗМЕРНЫХ АНТЕНН

PACS number: 94.20.Bb Purpose: A modification of the Doppler Interferometry Technique is suggested to enable estimating angles of arrival of comparatively broadband HF signals scattered by random irregularities of the ionospheric plasma with the use of small-size near-omnidirectional antennas. Desing/methodology/approach: The technique is based on the measurements of cross-spectra phases of the probe radiation recorded at least in three spaced points. Findings: The developed algorithm has been used to investigate the angular and time-and-frequency characteristics of HF signals propagating at frequencies above the maximum usable one for the direct radio path Moscow–Kharkiv. The received signal spectra show presence of three families of spatial components attributed, respectively, to scattering by plasma irregularities near the middle point of the radio path, ground backscatter signals and scattering of the sounding signals by the intense plasma turbulence associated with auroral activations. It has been shown that the regions responsible for the formation of the third family components are located on the equatorial slope of the maximum of the precipitating particle energy. The drift velocity and direction of the polar ionosphere plasma has been determined. Conclusions: The obtained estimates are consistent with the classical conception on the magnetospheric convection and plasma convection in the polar regions and do not contradict to the results of investigations of the auroral ionosphere dynamics using the SuperDARN network. Key words: ionospheric plasma, scattering, direction finding, polar ionosphere, auroral oval, velocity and direction of plasma drift Manuscript submitted 01.06.2016 Radio phys. radio astron. 2016, 21(3): 231-241 REFERENCES 1. Afraimovich, E. L., 1982. Interference methods of ionospheric radio sounding. Moscow: Nauka Publ. (in Russian). 2. Reinisch, B. W., 1996. Modern Ionosondes. In: H. Kohl, K. Schlegel, eds. Modern Ionosphere Science. Katleburg-Lindau: European Geophysical Society, pp. 440–458. 3. Reinisch, B. W. and Galkin, I. A., 2008. A new digisonde for research and monitoring applications. In: XXIX GA URSI, August 7-16, 2008: Abstracts. Chicago, Illinois, USA, p. 131. 4. REINISCH, B. W., SCALI, J. L. and HAINES, D. M., 1998. Ionospheric drift measurements with ionosondes. Ann. Geophys. vol. 41, no. 5-6, pp. 695–702. DOI: 10.4401/ag-3812. 5. GALUSHKO, V. G., 1997. Frequency-and-angular sounding of the ionosphere. Telecommunications and radio engineering. vol. 51, no. 6-7, pp. 1–6. DOI: https://doi.org/10.1615/TelecomRadEng.v51.i6-7.10 6. Galushko, V. G., Yampolski, Y. M. and Reinisch, B. W., 2000. Frequency-and-Angular Sounding of the Ionosphere with the Use of a DPS Receive System. In: Progress in Electromagnetics Research Symposium (PIERS-2000), July 5-14, 2000: Proceedings. Cambridge, MA, USA, p. 603. 7. Galushko, V. G. and Lytvynenko, G. V., 2001. Recovering the Three-Dimensional Structure of Ionospheric Electron Density Distribution by Angular-and-Frequency Sounding. Radio Phys. Radio Astron. vol 6, no. 3, pp. 222–229 (in Russian). 8. GALUSHKO, V. G., BELEY, V. S., KOLOSKOV, A. V., YAMPOLSKI, Y. M., PAZNUKHOV, V. V., REINISCH, B. W., FOSTER, J. C and ERICKSON, P., 2003. Frequency-and-angular HF sounding and ISR diagnostics of TIDs. Radio Sci. vol. 38, is. 6, id. 1102. DOI: https://doi.org/10.1029/2002RS002861 9. PAZNUKHOV, V. V., GALUSHKO, V. G. and REINISCH, B. W., 2012. Digisonde observations of TIDs with frequency and angular sounding technique. Adv. Space Res. vol. 49, no. 4, pp. 700–710. DOI: https://doi.org/10.1016/j.asr.2011.11.012 10. GALUSHKO, V. G., KASCHEEV, A. S., PAZNUKHOV,V. V., YAMPOLSKI, Yu. M. and REINISCH, B. W., 2008. Frequency-and-angular sounding of traveling ionospheric disturbances in the model of three-dimensional density waves. Radio Sci. vol. 43, is. 4, id. RS4013. DOI: https://doi.org/10.1029/2007RS003735 11. BRAUDE, S. Ya., MEN', A. V. and SODIN, L. G., 1978.The UTR-2 decameter wavelength radio telescope. In: Antenny. Moscow: Svyaz'. is. 26, pp. 3–15 (in Russian). 12. Gething, P. J., 1978. Radio direction-finding and the resolution of multicomponent wave-fields. Stevenage, England: Peter Peregrinus. 13. BIBL, K. and REINISCH, B. W., 1978. The Universal digital ionosonde. Radio Sci. vol. 13, is. 3, pp. 519–530. DOI: https://doi.org/10.1029/RS013i003p00519 14. RYTOV, S. M., KRAVTSOV, Yu. A. and TATARSKI, V. I., 1978. Introduction to statistical radiophysics. Part 2: Random fields. Moscow: Nauka Publ. (in Russian). 15. Kashcheyev, S. B., Zalizovski, A. V., Sopin, A. A. and Pikulik, I. I., 2013. On the possibility of bistatic HF ionospheric sounding by exact time signals. Radio Phys. Radio Astron. vol. 18, no. 1, pp. 34–42 (in Russian). 16. Brunelli, B. E. and Namgaladze, A. A., 1988. Physics of the ionosphere. Moscow: Nauka Publ. (in Russian). 17. JAYACHANDRAN, P. T., Macdougall, J. W., ST-MAURICE,J.-P., MOORCROFT, D. R., NEWELL, P. T. and PRIKRYL, P., 2002. Coincidence of the ion precipitation boundary with the HF E-region backscatter boundary in the dusk-midnight sector of the auroral oval. Geophys. Res. Lett. vol. 29, is. 8, pp. 97-1–97-4. DOI: https://doi.org/10.1029/2001GL014184 18. JAYACHANDRAN, P. T., DONOVAN, E. F., MACDOUGALL, J. W., MOORCROFT, D. R., ST-MAURICE, J.-P. and PRIKRYL, P., 2002. Super DARN E-region backscatter boundary in the dusk-midnight sector – tracer of equatorward boundary of the auroral oval. Ann. Geophys. vol. 20, pp. 1899–1904. DOI: https://doi.org/10.5194/angeo-20-1899-2002

SuperDARN E-region backscatter boundary in the dusk-midnight sector – tracer of equatorward boundary of the auroral oval

Abstract. We compare the locations of the equatorward boundaries of SuperDARN E-region backscatter and Hb emissions, focusing on the dusk-midnight sector of the auroral oval where the proton aurora is statistically located equatorward of the discrete electron aurora. We show that, whenever both boundaries can be simultaneously identified, they are coincident. Our result complements earlier studies, which demonstrated the correspondence between the DMSP b2i boundary and both the equatorward boundary of the proton auroral oval (Donovan et al., 2002), and the equatorward boundary of SuperDARN E-region echoes (Jayachandran et al., 2002). Further, our result shows that, provided there is sufficient precipitating proton energy flux, the SuperDARN radars can be used to monitor the equatorward edge of the proton auroral oval.Key words. Ionosphere (auroral ionosphere; particle precipitation; ionospheric irregularities)

Coincidence of the ion precipitation boundary with the HF E region backscatter boundary in the dusk‐midnight sector of the auroral oval

We have examined the location of the SuperDARN E region ionospheric backscatter boundary in the dusk‐midnight sector and compared it with the equatorward boundary of the hard ion precipitation (b2i) determined from the DMSP satellite particle spectrograms in the dusk‐midnight sector of the auroral oval. The locations of these two boundaries were found to be nearly coincident. This study evinces the capability of the SuperDARN radars to monitor the equatorward ion precipitation boundary (diffuse auroral boundary) and its dynamics irrespective of magnetic activity.

Mid‐ and low‐latitude prompt‐penetration ionospheric zonal plasma drifts

We have used ion drift observations from the DE‐2 satellite to determine the latitudinal variation and the temporal evolution of mid‐ and low‐latitude prompt penetration zonal plasma drifts driven by magnetospheric electric fields. Our results indicate that sudden increases in convection lead to predominantly westward perturbation drifts which decrease equartorwards and have largest amplitudes in the dusk‐midnight sector. The diurnal perturbation drift patterns shift to later local times with increasing storm time and decay to new quasi‐equilibrium values in about 2 hours, as the ring current readjusts to the new polar cap potential. The daily and latitudinal variations and temporal evolution of the DE‐2 prompt penetration drifts are generally in good agreement with predictions from the Rice Convection Model, although the experimental results show larger amplitudes and longer shielding time constants.

Response of equatorial ionosphere to the transit of interplanetary magnetic cloud of January 13–15, 1967. Transient disturbance in F region

Quarter-hourly ionograms of Kodaikanal (10°4′N, 77°29′E, dip 3°N) are analysed to evaluate the response of equatorial ionosphere to the severe geomagnetic storm (| Dst|max, 176 nT) associated with the transit of an interplanetary magnetic cloud at Earth during January 13–15, 1967. It is shown that during the early stage of the storm initial phase on January 13, which corresponded to the local dusk-midnight sector, the entire bottomside F region over Kodaikanal experienced a sudden and spectacular downward drift for a short-duration of ∼2 h (18:45 – 20:30 L.T.). The decrease in height of F layer peak ( hm) by 223 km over the interval 18:45–20:30 L.T. implied a gross apparent downward drift of ∼35.4 m s −1. The height disturbance occured during the recovery phase of an auroral substorm (bay disturbance) that developed at the commencement of the geomagnetic storm. It also displayed an apparent temporal association with a prominent northward swing in IMF Bz and decrease in polar cap potential drop, φ, estimated from IMF parameters. The anomalous and rapid post-sunset descent of F layer was accompanied by an increase in electron density at and below the F layer peak. The evident perturbation in F region height near the dip Equator is interpreted as the signature of a transient westward electric field disturbance generated by the decrease in magnetospheric convection (decrease in polar cap potential) during the recovery phase of the substorm. The values of vertical downward drift derived from the time rate of change of h′F and corrected for chemical loss effects indicated the maximum amplitude of the westward electric fields to be ∼1.9 mV m −1. The increase in Nm is shown to be the outcome of the ionization convergence rate induced by the abnormally large downward drift exceeding the chemical loss rate ( βNe) at altitudes ⩾250 km.

Intensification and fading of auroral arcs in the dusk‐midnight sector of the polar cap

Observations of the aurora from South Pole station (magnetic latitude = −74.2°) have been used to study the intensification and fading of polar arcs observed near the dusk meridian. Most of the cases examined have the following features in common: (1) a preexisting auroral form intensifies for about 10 min; (2) this activation is followed by a pronounced decrease of luminosity; (3) the auroral fade terminates after 30–60 min with the onset of intense aurora which sweeps rapidly overhead. The brief intensifications involve O (630.0 nm) enhancements of 0.1–0.3 kR and N2+ (427.8 nm) enhancements of 0.3–1.5 kR giving an emission ratio which in each case is consistent with the precipitation of electrons with an average energy of 3–12 keV, assuming a Maxwellian distribution. The auroral brightening is not accompanied by riometer absorption. Ground magnetic perturbations of the order 20–40 nT occur, and in about half the instances, weak broadband impulsive hiss is present. The availability of all‐sky camera, auroral electrojet (AE) index and interplanetary magnetic field (IMF) data for some of the cases enables the following additional characterizations of these events. The preexisting form is a Sun‐ or oval‐aligned arc (or part of a multiple arc system) which disappears following the activation; equatorward drift of the arc (or system) accompanies the luminosity change. There is some evidence to suggest that the arc is poleward of the auroral oval. The brief intensification and/or the onset of fading occurs during the growth phase or near the start of the expansive phase of a substorm; termination of the fade is near the maximum in AE and is probably indicative of the beginning of the recovery phase of the substorm. For all three cases for which IMF data were available the onset of fading occurred 20–30 min after Bz turned southward. Two of these cases were preceded by auroral arc enhancement when Bx was sunward; in the third case there was no prior enhancement when Bx was zero or slightly antisunward. By was negative (dawnward) in each case. Sun‐aligned arcs are a common feature of the polar cap during northward Bz but disappear during the increasingly disturbed conditions that accompany southward Bz. The present results suggest that brief intensifications of southern hemisphere polar cap arcs near dusk may be linked in part to the sunward orientation of the IMF which favors enhanced electron fluxes in the southern lobe of the magnetotail.