THE REACTION OF MID-LATITUDE IONOSPHERE ON STRONG IONOSPHERIC STORMS ON THE BASE OF THE EAST- SIBERIAN GROUND-BASED RADIO INSTRUMENT NETWORK DATA B.G. Shpynev, A.V. Tashchilin, A.P. Potekhin, V.I. Kurkin, A.V. Medvedev, K.G. Ratovsky, A.V. Zavorin and E.L. Afraimovich Institute of Solar-Terrestrial Physics, , P.O. Box 4026, Irkutsk, Russia

In present study we conduct the analysis of mid-latitude ionosphere dynamics during strong magnetic storms on the base of East-Siberian ground-based radio instrument network for years. For these events we investigate their common features. For analysis we used data from Irkutsk Incoherent Scatter Radar (ISR), Russian chirp-sounder network data, vertical sounding data from Digisondes (DPS-4) and data from GPS receivers. For comparative analysis we considered only strong storms when ionosphere effects had clearly defined character and ionosphere structure was significantly changed. We considered the events: These geomagnetic perturbations were registered at different seasons that allows us to study general regularities and differences in manifestation of strong geomagnetic perturbations in mid-latitude ionosphere. September 25, 1998 July 15-16, 2000 March 19-20, 2001 April 17-20, 2002 May 27-30, 2003 October 29-31, 2003 November 9-12, 2004 January 17, 2005

Irkutsk Incoherent Scatter Radar (ISR) Range of frequencies( ) MHz Peak output power3,2 MW Pulse duration mcs Type of antenna Sectorial horn Antenna gain(35-38)dB Angular size of the beam 0.5 x 10 degree Scan sector -30 : +30 degree PolarizationLinear Irkutsk’s Incoherent Scatter Radar

Chirp-sounder or FMCW ionosonde ( ionosonde with linear frequency modulation )

Digisonde ( DPS-4 sounder )

The locations of the instruments FMCW radio path Ground projections of ISR beam at various heights ISR beam inclination was 16  from a vertical

Basic conditions in mid-latitude ionosphere before strong storm During the strong storm we can separated three stages of its development in mid-latitude ionosphere:  Stage when i onosphere reply to active processes at high latitudes and when auroral oval spreads on mid-latitudes (Spreading stage);  Realignment of magnetosphere circulation to convectional type, changing of ion composition and neutral wind parameters, that produce significant changing in ionosphere structure (Stage inside the active area).  Restoration Stage, turning of the ionosphere to undisturbed co-rotational type.  Co-rotational type of the magnetosphere plasma circulation  Rather high (comparing to the polar ionosphere) electron density  Balance between the ionization, recombination, electron density, temperature and ion composition.

Spreading stage  When storm develops in polar oval region, on the oval border the Acoustic- Gravity Waves (AGW) are generated, which pronounced in the experiment as traveling ionospheric disturbances (TIDs). The common feature of this process is that they have very specific quasi-period: from minutes at the storm beginning to minutes at the end of this stage.  There exist a number of classical work describing AGV/TID propagation, but why the AGV/TIDs period is such uneven is still subject for discussion. Hunsucker R.D., Atmospheric gravity waves generated in the high-latitude ionosphere: A review, Revs. Geophys., 20, 293, Balthazor, R.L. and R.J. Moffett, Morphology of large-scale traveling atmospheric disturbances in the polar thermosphere, J. Geophys. Res., Vol. 104, No. A1, 15-24, Kirchengast G., Education of the physics of the gravity wave – TID relationship with the aid of theoretical simulation, J. Geophys. Res., Vol. 101, NO. A6, ,  We suggested that as far as strong magnetic storms is caused by proton events on Sun, the magnetosphere dynamics also must be determined by solar winds parameter. In particular we examine the solar wind proton density variations by using the data provided by NOAA satellites (  In the dynamics of solar wind proton density (with energy eV) we found irregularities which appear with periods of minutes and with periods of minutes.

April 17,2002 Ne (300km)

September 24,1998 Ne (300km)

July 15, 2000 Ne (300km)

March 19-20, 2001 Ne (300km)

May 29, 2003 Ne (300km)

January 17, 2005 Ne (300km)

November 9-10, 2004 Ne (300km)

Spreading stage ends when border of active zone (polar oval) come through point of observation. Beginning with this moment structure of magnetosphere circulation change to convectional type, and we observe abrupt reduction of electron density in 3-5 once when ionospheric plasma quickly leak out along opened tube in internal magnetosphere. Just before the abrupt Ne reduction the positive Ne disturbances are observed. We suggest that it is result of changing in neutral wind parameters. The suggestion that observed AGV/TIDs caused by a global source is supported by observations of similar structures by Russian Chirp Sounders network, by data from GPS receiver network and by data of Eurasian magnetometers. All these data show that variations of electron density and geomagnetic field variations appear simultaneously in large- scale area, which size comparable with the size of polar oval ( km).

Stage inside active area It characterized by:  Low electron density.  High electron and ion temperature.  Changing of ion composition  Fast-changing and strong irregularity on the altitudes of E-layer ( km), which is observed by Irkutsk ISR as coherent echoes. Coherent echo Geometry

1 km UT The mentioned before period in solar wind proton density (15-25 minutes) was found during the analyzing of coherent echoes spectra, when peak of Farley- Buneman spectra shifts periodically around carrier frequency. (Poster section in detail). Coherent echoes during July 15, 2000 Storm

Restoration stage  Structure of magnetosphere convection becomes again co-rotation, but tubes are empty, that produce effect of positive disturbing in all parameters.  The first day after the storm shows higher temperature (Te by K, Ti by K) especially in the morning.  Large (by 15-30%) daytime electron density values are observed.  Moving from North-East Irregularities of Ne (20-30%) with scale km, are often observe.

In the progress of strong storms for mid-latitude observatory three stages are clearly manifested in the ground based experiments: 1. Spreading of auroral oval to mid-latitudes; 2. Stage inside active area when the structure of the ionosphere changes dramatically; 3. Recovery stage. First stage is characterized by the generation of quasi-periodical TIDs, which sources are, probably, the variations of solar winds proton density. Abrupt depletion of Ne characterize the changing of the magnetosphere circulation to convectional type. Just before this fall the positive Ne disturbance is often observed. Coherent echoes are usually observed by Irkutsk ISR radar after such realignment. On the recovery stage the higher Ne values (by 15-30%) and the higher temperatures (on К ) are observed in the daytime. Also on the recovery stage km Ne disturbances are observed. Conclusions

Thank You! The work and trip to the URSI GA 2005 were supported by the Russian Fund of Basic Research