STUDI GELOMBANG ULF: KORELASI PULSA MAGNET Pc3 DENGAN KECEPATAN ANGIN SURYA DAN MEDAN MAGNET ANTARPLANET

Energy for the Earth’s magnetospheric processes is provided by solar wind. Pc3 magnetic pulsation is one of geomagnetic ULF wave. Pc3 magnetic pulsation has been studied to understand the dynamic of magnetosphere. Geomagnetic pulsations are quasi-sinusoide variations in the Earth’s magnetic field in the period range of 10-45 seconds. The magnitude of these pulsations ranges from fraction of a nT (nano Tesla) to several nT. These pulsations can be observed in a number of ways such as applied of ground based magnetometer. We used the magnetometer data of Manado, Parepare, and Kupang stations to studied the effect of the solar wind and interplanetary magnetic field on these pulsations. To extract Pc3 magnetic pulsations we applied second order of Butterworth filter and using Hamming windowing. The result showed that Pc3 magnetic pulsation have correlation with increasing solar wind velocity and interplanetary magnetic field-IMF, it is mean that solar wind controls Pc3 magnetic pulsations occurrence. AbstrakAngin surya merupakan sumber energi bagi proses-proses fisis yang terjadi di magnetosfer Bumi. Untuk dapat memahami dinamika di magnetosfer Bumi dapat di tinjau dari gelombang ULF salah satunya pulsa magnet Pc3. Pulsa magnet Pc3 merupakan variasi quasi-sinusoide pada medan magnet Bumi dalam rentang periode 10 – 45 detik. Pulsa magnet Pc3 umumnya memiliki amplitudo rendah dengan rentang nT (nano Tesla). Terdapat beberapa cara yang dapat dilakukan untuk mengamati pulsa magnet Pc3 diantaranya dengan menggunakan magnetometer landas Bumi. Dalam makalah ini kami menggunakan data pengamatan magnetometer stasiun Kupang, Manado, dan Parepare untuk mempelajari hubungan pulsa magnet Pc3 terkait dengan angin surya dan medan magnet antarplanet. Pulsa magnet Pc3 diekstrak dari data variasi medan magnet dengan menggunakan Butterworth Filter dan Hamming windowing. Hasil yang diperoleh menunjukkan bahwa pulsa magnet Pc3 memiliki korelasi dengan peningkatan kecepatan angin surya dan medan magnet antarplanet. Hal ini mengindikasikan bahwa angin surya merupakan salah satu sumber yang mengontrol perubahan yang terjadi pada pulsa magnet Pc3.

Pc5 modulation of high energy electron precipitation: particle interaction regions and scattering efficiency

Using the NORSTAR riometer and CANOPUS magnetometer arrays we have investigated the modulation of high energy electron precipitation by ULF waves in the Pc5 frequency band. We conducted two separate studies of Pc5 activity in the riometers. The first is an independent survey of three riometer stations in the Churchill line (one at each sub-auroral, auroral, and typical polar cap boundary latitudes) in which we identified all riometer Pc5-band pulsations over 11 years. All had a corresponding magnetometer pulsation implying that a magnetic pulsation, is a necessary condition for a riometer pulsation (in the Pc5 Band). We find seasonal and latitude dependencies in the occurrence of riometer pulsations. By a factor of two, there are more riometer pulsations occurring in the fall-winter than the spring-summer. At higher latitudes there is a tendency towards noon pulsations during the spring-summer, suggesting that the criteria for riometer pulsations is affected by the dipole tilt. Our second study was based on the previous magnetometer study of Baker et al. (2003). Using the database of Pc5 activity from that study we were able to select the riometer Pc5 pulsations which adhere to the strict Pc5 definition in the magnetometer. We find that roughly 95% of the riometer pulsations occurred in the morning sector compared to 70% in the magnetometer. Given a magnetometer pulsation at Gillam in the morning sector, there is a 70% chance of there being a corresponding riometer pulsation. The morning sector probabilities at Rankin (geomagnetic (PACE) latitude 74°) and Pinawa (61°) are 3% and 5%, respectively. These statistics suggest there is a localized region in the pre-noon magnetosphere where Pc5 band ULF activity can modulate high energy electron precipitation. We also find that riometer pulsations display a Kp selection towards mid (i.e. 3–4) activity levels which mimics the product of the Kp dependence of high-energy electron fluxes on the dawn side (from CRRES) and all magnetic Pc5 activity. A superposed epoch analysis revealed that the elevated electron flux needed to produce a riometer pulsation is most likely provided by substorm injections on the nightside. We also find that the amplitude of modulated precipitation correlates well with the product of the background absorption and the magnetic pulsation amplitude, again leading to the idea that a riometer pulsation needs both favorable magnetospheric electron flux conditions and large enough magnetic Pc5 wave activity. We further separate our pulsations into field line resonances (FLRs), and non-field line resonances (non-FLRs), as identified in the Baker et al. (2003) survey. We find that FLRs are more efficient at modulating particle precipitation, and non-FLRs display an amplitude cutoff below which they do not interact with the high energy electron population. We conclude that the high energy electron precipitation associated with Pc5 pulsations is caused by pitch angle scattering (diffusion) rather than parallel acceleration. We suggest two future studies that are natural extensions of this one. Keywords. Energetic Particles/Precipitating; Wave-Particle Interactions; Auroral Phenomena

Bursts of ULF noise excited by sudden changes of solar wind dynamic pressure

We present the results of analysis of the dayside magnetic pulsation response to a sudden change in solar wind dynamic pressure. We concentrate on the events when a burst or a series of short-lived bursts in the Pc1 frequency range with the repetition period of 7–15 min were observed on the ground around the local noon. Not every impulse of large amplitude caused this phenomenon. We have found that the ULF bursts were excited when the spectrograms of the DMSP satellites showed a signature of 10–30 keV ions in the vicinity of the magnetic flux tube of the ground observatory, that may be related to a geomagnetic storm preceding the event. In light of this finding a possible model of the phenomenon is suggested in which the hot protons influence significantly both the generation and modulation of Pc1 activity.Key words. Magnetospheric physics (solar wind – magnetosphere interaction; MHD waves and instabilities; storms and substorms)

Appraisal of electromagnetic induction effects on magnetic pulsation studies

The quantification of wave polarization characteristics of ULF waves from the geomagnetic field variations is done under ‘a priori’ assumption that fields of internal induced currents are in-phase with the external inducing fields. Such approximation is invalidated in the regions marked by large lateral conductivity variations that perturb the flow pattern of induced currents. The amplitude and phase changes that these perturbations produce, in the resultant fields at the Earth’s surface, make determination of polarization and phase of the oscillating external signals problematic. In this paper, with the help of a classical Pc5 magnetic pulsation event of 24 March 1991, recorded by dense network of magnetometers in the equatorial belt of Brazil, we document the nature and extent of the possible influence of anomalous induction effects in the wave polarization of ULF waves. The presence of anomalous induction effects at selected sites lead to an over estimation of the equatorial enhancement at pulsation period and also suggest changes in the azimuth of ULF waves as they propagate through the equatorial electrojet. Through numerical calculations, it is shown that anomalous horizontal fields, that result from induction in the lateral conductivity distribution in the study region, vary in magnitude and phase with the polarization of external source field. Essentially, the induction response is also a function of the period of external inducing source field. It is further shown that when anomalous induction fields corresponding to the magnitude and polarization of the 24 March 1991 pulsation event are eliminated from observed fields, corrected amplitude in the X and Y horizontal components allows for true characterisation of ULF wave parameters.Key words. Geomagnetism and paleomagnetism (geomagnetic induction) – Ionosphere (equatorial ionosphere) – Magnetospheric physics (magnetosphere-ionosphere interactions)