Study of Solar Proton Event Observed using Riometers

Proceedings of the National Symposium on Current trends in Atmospheric Research including Communication And Navigation aspects (CARCAN-), Vignana Bharathi Institute of Technology, Hyderabad, A.P. December -,. pp.-. Study of Solar Proton Event Observed using Riometers S.S. Nikte, A.K. Sharma, R.S. Vhatkar, D.P. Nade, G.A. Chavan, R.N. Ghodpage 3, M.V. Rokade, P.T. Patil and R.V. Bhonsle, Space and Earth Science Laboratory, Shivaji University, Kolhapur. 3 Indian Institute of Geomagnetism, New Panvel, Navi Mumbai. Email: aks_phy@unishivaji.ac.in, ABSTRACT Solar proton events have been observed, as Polar Cap Absorption (PCA), using identical riometers operating at 3 MHz, simultaneously, at three Australian Antarctic stations in southern hemispheres. During these events, high-energy protons precipitate into the middle atmosphere in the Polar Regions and causing ionization in the lower ionosphere. We investigated the observations made on th August, of ionospheric absorption obtained by a 3 MHz riometers. We have compared the Cosmic Noise Absorption (CNA) with proton flux and various geomagnetic indices. The linear relation is observed between proton flux and CNAs. The maximum absorption of.6 db,.79 db and.8 db were recorded on Casey, Mawson and Davis stations, respectively. Keywords Ionospheric absorption, solar proton event, riometer cosmic radio noise. INTRODUCTION In the history of radio physics, solar proton events (SPE), also known as polar cap absorption (PCA) events, begin as emission of electrons and ions from the surface of the Sun. The ions are mostly protons ( 9%) but heavier particles are also emitted, the relative abundances being similar to those in the solar corona. For the most energetic coronal mass ejections (CME), particle energies can be up to MeV or even GeV level, thus far exceeding the normal solar wind values, e.g. kev for protons. The enhancement in ionization of D-region is due to precipitation of high-energy protons []. Ionospheric disturbances during solar proton events have been observed almost by radio techniques, especially by riometers and incoherent scatter radars. As particles propagate down into the atmosphere they lose their energy in collisions with atmospheric gases. In such a collision, due to energy of protons atmospheric molecules gets ionized, and an ion-electron pair is created. In addition to the primary protons, the secondary electrons produced in ionization may have enough energy to further ionize and dissociate atmospheric gases. Approximately 36 ev of energy is required in the production of one ion pair [], thus a proton with MeV initial energy is able to ionize about 8, molecules along its path before all the energy is lost. The atmospheric penetration depth is dependent on the particle energy, the MeV solar protons depositing their energy in the mesosphere and stratosphere [3]. Solar protons with energies higher than MeV can penetrate down to stratospheric heights (3 km). Bailey [] suggested the enhancement in ionization of ionospheric D-region is due to precipitating high-energy protons of solar origin. The lower ionospheric characteristics during SPEs have been studied using riometer measurements of cosmic radio noise absorption [-7]. SPEs provide a direct connection between the Sun and the Earth s middle atmosphere. They are relatively sporadic but tend to be more probable during times of maximum solar activity. Ten to twelve of SPEs may occur during a solar cycle, but only in few cases the protons have energies sufficient to penetrate down to the stratopause region. However, those cases are extreme examples of solar forcing on the middle atmosphere and can significantly affect the lower ionosphere and middle atmosphere. The magnitude of an SPE can be determined using the particle flux unit (pfu) for > MeV protons and given in cm - sr - s -. Generally during solar flare, protons of relativistic energies arrive at Earth within minutes after the onset. Attaining a maximum intensity within tens of minutes after onset these energetic proton flux decays to background values in several hours, much faster than more abundant low-energy protons. After the occurrence of the solar particle event, the lower-energy proton flux decay to background values over a several day period. These particles observed as polar cap absorption events by riometers, which record cosmic radio noise at chosen frequencies. Absorption is due to enhanced ionization of the atmosphere below km [8]. All three riometers are operated at a fixed frequency of 3 MHz. Hence, such a continuous recording throughout a given SPE are available for complete study. In this study we compared

Proceedings of the National Symposium on Current trends in Atmospheric Research including Communication And Navigation aspects the SPE absorption with proton flux at > MeV pfu >3 MeV pfu, >6 MeV pfu. The absorption during day time is produced in a relatively low region of the ionosphere, while nighttime absorption is due to a higher altitude region that ionizes chiefly by 3- MeV protons [9]. The lower ionospheric characteristics during SPEs, e.g. day/night differences and twilight asymmetries in electron density, have been studied using especially riometer measurements of cosmic radio noise absorption [].. SOLAR PROTON EVENT OF AUGUST, Solar activity was low during 3 st July st August, with C-class flares. Activity increased to moderate levels on nd August due to a long-duration M at /69 from Region 6, with associated Type IV, Type II (estimated speed of 67 km/s), and Tenflare ( sfu) radio emissions. Activity increased to high levels on 3 rd August with three M-class flares. The largest of these was an M6 at 3/38. A CME was subsequently observed in STEREO-A Cor imagery at 3/9. Solar activity remained at high levels on th August due to an M9 from Region 6 at /37, with associated Type IV, Type II (estimated speed of 7 km/s). A CME was also associated with the M9 flare with an approximate speed of km/s. Activity decreased to low levels on after th August []. For this study CNA data have been taken from Australian Antarctic divisions Casey, Mawson and Davis stations location is shown in table-. The Casey, Mawson and Davis stations has been recording data since January 989, December 989 and February 988 respectively. All are working on 3MHz with parallel dipole antenna and having wide beam. The data recording is arranged resolution of sec. Antenna scans the sky day and night and it receives the intensity of the cosmic radio noise. The riometer is simply a receiver that measures intensity of the random noise which impinges on the earth from space. In this paper we have studied SPE of th August,. The CNA data of riometer is compared with proton flux, Kp, AE, PC and Dst indices for the event and observed that the maximum value of each parameter is shown in table. The plasma or solar wind pressure, density, velocity, AE index, PC index and proton flux data from ACE is included in this paper. The data used in this paper for Kp, and Dst indices are taken from World data centre (WDC) for Geomagnetism, Kyoto, Japan. Table : Geographic latitude and longitude of Australian Antarctic stations Stations Geographic Latitude Geographic Longitude Casey (CAS) 66. S. E Mawson (MAW) 67.6 S 6.7 E Davis (DAV) 68.6 S 78. E 3. RESULT AND DISCUSSION The geomagnetic conditions in the near-earth space during the SPE events have been described in several papers, for example by Perrone et al [], we found that the various geomagnetic indices from th to 7 th August, varies with the solar proton flux with energy > MeV. This SPE event was registered by several satellites. The maximum of intensity of the solar proton flux (> MeV) was 96 cm - sr - s -. npa n/cc Km/s - 6-8 6 Pressure Density Speed 6 7 8 Days of August, Fig. : Geophysical situation during the SPE of th August,. The panels contains (from top to bottom): the plasma pressure (npa), density (cm-3), speed (Km/s). The Temporal variations in all the parameters are clearly seen on th August,. Figure shows main features of the geophysical conditions during SPE event of th August,. From this figure it is clear that the pressure, density, speed of the solar wind is enhanced after the period of major SPE (~ day). These results are in well agreement with previous study []. We also found that after one day of SPE, the geomagnetic indices were disturbed. Figure shows the variations in the AE and PC indices. The precipitating solar protons of great intensity produce significant ionospheric and atmospheric disturbances. The event was maximum on th August at UT. The plot

Study of Solar Proton Event Observed using Riometers of AE shows that the there is increase of Earth s magnetic field of up to 7 on August at around 3UT and Pc index was reached to 9.67 on the same day, shown in figure. A positive deviation in AE index is due to incident protons flux due which magnetosphere gets compressed, which results into sudden increment of the Earth s magnetic field. > 6 MeV PC Index Solar proton flux (pfu) - - 8 > 3 MeV > MeV 6 3 AE Index 6 7 8 Days of August, Fig. 3: Solar proton flux with energy > 6 MeV, >3 Mev and > MeV, (From top to bottom ) recorded during nd to 8 th September. The precipitation of solar proton flux of lower energy (> MeV) was peak value on 6 th September while higher energy proton flux was maximum on 3 rd September,. 6 7 8 Days of August, Davis Fig. : The temporal variations in AE and PC indices are clearly seen on th August,. Figure 3 shows solar protons flux > MeV, 3 MeV and 6 MeV respectively which are measured by ACE (these protons are responsible for excessive absorption in the ionospheric D-region) from the figure it is clear that the absorption was maximum on th August in all three stations. The other important feature is that solar protons flux of energy > Mev was also intense on the same day. Therefore, from both the observations (figures 3 and ) it is clear that absorption in the D-region of ionosphere is mainly due to the precipitation of protons with energy > MeV. The sudden increment in CNA on end of th August and 6 th August may be due to, two additional shock passages were seen by ACE at /7 and /83, (accompanied by a noticeable increase in solar wind density, velocity) and activity increased to minor to severe storms during / - 6/6Z due to effects from the CME. The absorption of cosmic radio noise recorded by riometer is an evidence for enhancement in the ionization of ionospheric D region [3]. Absorption (db) 3 - - 6 7 Days of August, Mawson Casey Fig. : Example of SPE event of th August,. The top displays the cosmic noise absorption measured by the wide beam riometer of Davis Station. The middle panel shows the CNA recorded at Mawson station and the bottom panel displays the CNA of Casey station.

Proceedings of the National Symposium on Current trends in Atmospheric Research including Communication And Navigation aspects Table : Cosmic radio noise absorption during solar proton events of th August, and corresponding observations. Start (Day/UT) Aug /63 Particle Event Maximum (Day/UT) Aug / Proton Flux (pfu @ > MeV) 96 Maximum Absorption (db)on th and UT time In this analysis the min values of the proton flux of energy levels ( > MeV, > 3 MeV and > 6 Mev) and the correspondent riometer absorption recorded at three Australian Antarctic divisions (Casey, Mawson and Davis) during the period th to 7 th August, were compared. The Consideration of the geophysical observations made in space (Figure -3) and groundbased observations by riometer (Figure ) are well matched. After getting maxima on th August of the proton flux gradually diminished to the background. The riometers demonstrated that the absorption of cosmic radio noise varied exactly with temporal variations of the solar proton flux in mostly at low energy. There was sharp increase both in solar proton (figure 3) flux and cosmic radio noise absorption (figure ) on th August as well as sharp increment observed in the solar wind, pressure, density and speed. A small but clearly positive peak of Dst on th August was a manifestation of these solar wind disturbances. A positive deviation in Dst (figure ) is generally taken to imply magnetospheric compression by the increased solar wind pressure, moving the magnetopause closer to the Earth. The negative deflections in the Dst index are caused by ring current. The ring current results from the differential gradient and curvature drifts of protons and electrons in the near earth region and its strength is depend on the solar wind Delay between SPE start time and Maximum absorption (in Hours) conditions. The negative deflection due to SPE was observed on 6 th August near to UT and it was -3. The quiet to unsettled geomagnetic activity (Kp<3), was observered on August, the Kp observed on the same day as demonstrated in the figure 6. Towards the end of th August an interplanetary shock struck the magnetosphere leading to enhanced geomagnetic activity; Kp jumped from to 8 as the absorption became much more variable. This event began late on th August and maximum observed on August. A number of negative spikes occured suggesting enhanced solar radio emission. Kp Index 9 8 7 6 3 Maximum deviations in Various geomagnetic indices during SPE Casey Mawson Davis Casey Mawson Davis Kp AE Dst PC.6/ 6.79/ 7.8/ 7 :6 3: :6 8 7-3 9.67 to 8 August - - -6-8 - - 6 7 8 9 Days of August, to August Fig. : A positive deviation in Dst (due to solar wind pressure) is generally taken to imply magnetospheric compression. The negative deviation in Dst due to sudden decrement in earth magnetic field due to opposite magnetic field induced by ring current. 6 7 8 9 Days of August, Fig. 6: The Kp index for the event which start with on August and reach to 8 on August.. CONCLUSIONS. The solar proton event of energy > MeV at geosynchronous orbit began at 63 UT on 3rd September, in response to the M9 flare on th August at 37 UT.. The maximum values of CNA on th August at Casey, Mawson and Davis stations were.6 db,.79 db and.8 db, respectively. 3. The time interval between start time of SPE and maximum value of CNA was observed nearly hours and 6 min for Casey station, 3 hours and min for Mawson station and hours and 6 min for Davis station. 3

Study of Solar Proton Event Observed using Riometers. The satellite observations of various parameters and geomagnetic indices (during SPE) are well coincide with the ground based observations of CNA by riometer at 3 MHz.. It is observed that the absorption of cosmic radio noise in the ionospheric D- region during SPE is mostly due to the lower energy (> MeV) solar proton flux. ACKNOWLEDGMENT We are thankful IPS world data centre for providing suitable Riometer data of Casey, Mawson and Davis stations. We would like to give special thanks to Prof. Michel Hyde and Michael Kehe Wang for their constant encouragement and fruitful discussions during presented work. The list of solar proton events were obtained from the NOAA (National Oceanic and Atmospheric Administration) (http://www.swpc.noaa.gov/ftpdir/indices/spe.txt) and proton flux data from ACE satellite. Geomagnetic index data were provided by the WDC for Geomagnetism, Kyoto, Japan. One of the authors Mr. S. S. Nikte is thankful to University grants commission (UGC), for providing financial support during the work. REFERENCES [] Bailey D. K., Planetary Space Science, (96) 9. [] Rees M. H., Physics and chemistry of the upper atmosphere, Cambridge atmosphericand space science series, Cambridge University Press, Cambridge, UK (989). [3] Hargreaves J. K., The solar-terrestrial environment, Cambridge Atmospheric and Space Science Series, Cambridge University Press, Cambridge, UK (99). [] Bailey D. K., Planetary Space Science, (96) 9. [] Chivers H. J. A., Hargreaves J. K., Conjugate Planetary and Space Science, 3 (96) 83. [6] Reid G. C., J. Geophys. Res., 66 (96) 7. [7] Gillmor C. S., J. Atmos. Terr. Phy., (963) 63. [8] Stoker P. H., Van Wyk J. P., J. Geophy. Res., 98, A (993) 9. [9] Bach Sellers, Frederick A., Hanser Michael A., Stroscio G., Kenneth Yates, Radio Science, (977) 779. [] Gillmor, C. S., J. Atmos. Terr. Phy., (963) 63. [] http://www.swpc.noaa.gov/weekly/_weeklyp DF/prf87.pdf [] Perrone L., Alfonsi L., Romano V., and de Franceschi G. Ann. Geophy., () 633. [3] Armstrong T. P., Laird C. M., Venkatesan D., Krishnaswamy S., Rosenberg T. J., J. Geophys. Res., 9 (989) 33.