Multi-instrument observations of atmospheric gravity waves/traveling ionospheric disturbances associated with enhanced auroral activity

Transcription

1 Multi-instrument observations of atmospheric gravity waves/traveling ionospheric disturbances associated with enhanced auroral activity Zama Katamzi-Joseph *, Anasuya Aruliah, Kjellmar Oksavik, John Bosco Habarulema, Kirsti Kauristie, and Michael Kosch * South African National Space Agency, Hermanus, South Africa. Dept. Physics & Electronics, Rhodes University, Grahamstown, South Africa. 4 th International ANGWIN Workshop, Brazil, April 2018

2 Atmospheric Gravity Waves/Traveling Ionospheric Disturbances (AGWs/TIDs) Traveling ionospheric disturbances manifestation of atmospheric gravity waves in the ionosphere appear as wave-like perturbations in measurements, e.g. TEC Classified into 2 main categories based on period, and horizontal speed or wavelength: Medium scale: periods minutes, horizontal speeds m/s and wavelength < km. Mostly associated with meteorological events (Mayr et al., 1984; Hernàndez-Parajes et al., 2006). Large scale: periods > 30 minutes, horizontal speeds > 400 m/s and wavelength > 1000 km. Typically associated with disturbed geomagnetic conditions (Ding et al, 2006). Aim: determine characteristics and source of AGWs/TIDs observed in GNSS and FPI measurements during night of 6 January 2014

3 Data GNSS receivers (University of Bergen, Norway): GPS total electron content (TEC), 60 s cadence, FPI (University College London): 630 nm intensity, emission height 240 km, 30 elevation angle, 9 minutes cadence All sky camera (Finnish Meteorological Institute): nm intensity, emission height 110 km, 1 minute cadence Magnetometers (IMAGE): Horizontal X component, 1 minute cadence

4 Method: SADM-GPS Velocities obtained from Statistical Angle of Arrival and Doppler method for GPS radio interferometry by Afraimovich et al. (1998). Also used by Valladares and Hei (2012) and Habarulema et al. (2013) Assume TID is plane sinusoidal traveling wave: I x, y, t = A sin(ωt k x x k y y + φ 0 ) TEC TID amplitude x and y components of wave number k Initial disturbance phase I x = y KHO DTEC HOP DTEC BJN y BJN (DTEC HOP DTEC KHO ) x KHO y BJN x BJN y KHO I y = x BJN DTEC HOP DTEC KHO x KHO (DTEC HOP DTEC BJN ) x KHO y BJN x BJN y KHO I x and I y are functions of t Angular disturbance frequency

5 Azimuthal propagation direction of phase wavefront: α t = tan 1 u y(t) = tan 1 I y (t) u x (t) I x (t) Horizontal phase velocity v h t = u t + w x t sin α t + w y t cos(α(t)) w x = x IPP t + dt x IPP (t) dt Method: SADM-GPS u t = หu x(t) u y (t) ห u x 2 + u y 2 u x t = I t (t) and u I y t = I t (t) x I y I t = DTEC HOP t + dt DTEC HOP dt and w y = y IPP t + dt y IPP (t) dt

6 TEC Results TEC shows wave-like perturbations between 17 and 23 UT on 6 Jan 2014 Approximate diurnal trend by 4 th order polynomial and remove to get TEC perturbations, and therefore determine characteristics of wavelike perturbations (e.g. periods, velocities)

7 TEC Results A B C D Periods: normalised Lomb-Scargle least squares frequency analysis; 99.99% confidence level PRN 3 A: 29 minutes (KHO) B: 32 minutes (BJN) C: 37 minutes (HOP+KHO) D: 58 minutes (BJN + HOP) PRN 11: 39 minutes (BJN+KHO)

8 TEC Results PRN 3: <Vh> = 760 ± 235 m/s <α > = 347 ± 19 (east of north) poleward propagation PRN 11: <Vh> = 749 ± 267 m/s α = 345 ± 20 (east of north) poleward propagation

9 FPI Results p = 128 min Periodic enhancements in SE and SW between 15 and 02 UT Periodogram for data between 15 and 21 UT Period (ZEN and SW) = 128 minutes (2.1 hours) Period (SE) = 174 minutes (2.9 hours) Not enough information at different directions to determine propagation information

10 Polar Magnetic Indices Kp max: 1 and min Dst: - 10 nt quiet storm conditions Auroral geomagnetic disturbance observed, especially around 18UT AE max ~200 nt PCN max ~1.5 mv/m Minor substorm conditions

11 All sky Camera Results ASC keogram: intensity brightening at ~18 UT associated with aurora activity coincides with AGWs/TIDs observations Intensities extracted at specific latitudes corresponding to GPS receivers shows shift in intensities peaks Poleward propagation, virtual horizontal velocity ~823 ± 143 m/s

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13 ASC Results Periodogram shows periods of 41 minute and 49 minutes

14 Magnetometer Results * X-components obtained from SuperMAG shows disturbance around 18 UT Baseline: yearly trend Periodogram obtained using data shows period of 53 minutes for BJN and HOP stations * Ignored since greater than half the data length Horizontal speed and azimuth (used altered SADM-GPS): 708 ± 261 m/s, 2 ±29 east of north

15 Discussion Correlation of AGWs/TIDs characteristics from instruments sampling ionosphere/thermosphere at different heights TEC calculated assuming thin shell at 300km: period minutes, velocity m/s poleward; Intensities of nm emission assumed height at 110 km: periods minutes, velocity 823 m/s poleward; X-magnetic field deflection infers about ionospheric currents at also ~ 110 km: period 53 minutes, velocity 708 m/s poleward. The AGWs/TIDs similar characteristics as those of large-scale TID class. Characteristics comparable to other high latitudes studies, e.g. Nicolls et al. (2012): 32.7±0.3 min, 560±270 m/s, 33.5±15.8 (Alaska) Momani et al. (2010): m/s poleward propagation (Antarctica) Observations of similar velocities at various heights also observed by Shiokawa et al. (2003): Obtained 640 m/s from all sky imager, m/s from GPS and 580 m/s from ionosondes

16 Summary + Conclusion Presented AGWs/TIDs observed with measurements from radio, optical and magnetic field over Svalbard on a quiet geomagnetic night of 6 January 2014 Properties match large scale TID characteristics At same time substorm and auroral disturbances of similar periods and velocities observed from magnetometers and all-sky camera data. AGWs/TIDs generated through particle precipitation, Joule heating or Lorentz forcing

17 Thank You Zama Katamzi-Joseph 1,2, Anasuya Aruliah 3, Kjellmar Oksavik 4,5, John Bosco Habarulema 1,2, Kirsti Kauristie 6, and Michael Kosch 1,7,8 1 South African National Space Agency, Hermanus, South Africa. 2 Dept. Physics & Electronics, Rhodes University, Grahamstown, South Africa. 3 Dept. Physics & Astronomy, University College London, UK. 4 Dept Physics & Technology, University of Bergen, Norway. 5 Arctic Geophysics, University Centre in Svalbard, Norway. 6 Finnish Meteorological Institute, Finland. 7 Dept Physics, Lancaster University, UK. 8 Dept, Physics & Astronomy, University of the Western Cape, South Africa.

18 References Afraimovich, E., K. Palamartchouk, and N. Perevalova (1998), GPS radio interferometry of traveling ionospheric disturbances, J. Atmos. Sol. Terr. Phys., 60, , dio: /S (98) Habarulema, J., Z. Katamzi, and L.-A. McKinnell (2013), Estimating the propagation characteristics of large-scale traveling ionospheric disturbances using ground-based and satellite data, J. Gophys. Res. Space Physics, 118, , doi: /2013JA Valladares, C., and M. Hei (2012), Measurements of the characteristics of TIDs using small and regional networks of GPS receivers during the campaign of July of 2008, Int. J. Geophys., doi: /2012/