Ultra low frequency (ULF) waves incident within the Earth’s atmosphere are produced by means of approaches within the magnetosphere and solar wind. These approaches produce a wide variety type of ULF hydromagnetic waves. Distinctive frequencies of waves and polarizations originate in different regions of the magnetosphere. Extremely low frequency waves (magnetic pulsations) are because of hydromagnetic waves that can be generated due to different types of plasma instabilities inside the magnetosphere or on its boundary in a completely complicated manner. In this paper, the origination of hydromagnetic waves, their sources internal and external to the magnetosphere and their propagation and modification in the magnetosphere and ionosphere are in brief mentioned. A very good summary of those topics, with references to the most significant publication dealing with ULF waves, has elegantly been reported by McPherron
The intensity of magnetic disturbances will increase from low to high latitudes up to range of the auroral zones, i.e. approximately magnetic latitude 65o. In the high latitudes, magnetograms are seldom completely undisturbed. Intense magnetic storms generally commence abruptly at same moment all around the Earth. Further to large-scale magnetic storms there are disturbances of an awful lot shorter duration, along with polar magnetic sub-storms and bays. Abrupt impulsive change (surprising impulses) may also arise and are regularly determined simultaneously everywhere in the world and feature additionally been detected within the magnetosphere. Variation with periods more or less from 0.1s to 10min are grouped collectively and termed as geomagnetic micropulsations
The diurnal variation of occurrence and frequency of Pc3-4 waves recorded at ground station and their dependence on range and geomagnetic indices Kp and also identify their source and propagation modes. The present study describes the interaction of Pc4 ULF waves with solar wind and its dependence on Kp values.
The data of all of the stations has been sampled at 1s time interval. Digital dynamic spectra (DDS) for the north-south (X) east-west (Y) and vertical (Z) components of the recorded data had been constructed for every day for one year period. The X- and Y-components of these DDS have been investigated for undertaking the above diurnal and seasonal statistical study
Recording stations |
Geographic co-ordinates Long. °E Lat. ° N |
Geomagnetic co-ordinates Long. °E Lat. ° N |
||
Pondicherry(PON |
79.92 |
11.92 |
151.97 |
02.50 |
Nagpur (NAG) |
79.00 |
21.10 |
151.93 |
11.72 |
Hanle (HAN) |
78.97 |
32.78 |
151.89 |
23.38 |
The recorded time series of magnetic intensity with 1s period in-between period were filtered using a 0-phase shift sixth order Butterworth type “band pass” filter with limits of the frequency range 5-40 mHz
The variation of Pc4 occurrence on Kp values for January, 2005 is depicted in
All of these consequences are not depicted for carrying out brief reporting. Only one of the representative outcomes for the Spring season, 2005 represented in
The Kp dependence of Pc4 occurrence for the whole year 2005 is shown in
The investigation of the dependence of Pc4 event on Vsw turned into also undertaken for all the several months of the year. All these results aren't presented for carrying out brief reporting. Only one of the typical outcomes for the individual month of March, 2005 is presented in
The maximum value of duration of activities at Nagpur was observed to be 489 min similar to Vsw values of 400 - 450 km/s. At Hanle, the main peak of period turned into of 472 minute. Similar pattern were also found at Pondicherry with the maximum occurrence peek having duration of 490 min analogous to Vsw values of 400 - 450 km/s. The statistical consequences on the dependence of Pc4 occurrence on Kp and Vsw for the complete year 2005 provided entirely details. The dependence of Pc4 pulsations occurance on Vsw for the whole year 2005 observed at all the three stations is depicted in
Pc4 Magnetic Pulsation perceived on earth may either both be internal or external to the magnetosphere. This mechanism was observed to be most achievable for shorter wavelengths and prominent localization in longitude. Such localized waves were found in space at geostationary orbit
The Ist direct proof for the propagation of external Pc3-4 wave power into the magnetosphere has been introduced by Greenstadt et al.
In the light of the above examined excitation mechanism and the obtained results of the diurnal and seasonal variations of low latitude Pc4 pulsations, it is recommended that the upstream waves are a significant source of Pc4 pulsations recorded on the nightside which were started on the dayside and most likely by an extended region of ULF waves. It is also proposed that the plasmaspheric cavity mode reverberation may have assumed a role in sifting the broadband input to the magnetosphere. The results of the current examination are additionally in concurrence with the observed characteristic of ULF upstream waves
The month to month variation of Pc4 event has a Kp dependence range of 0 to 9-. However, the yearly Pc4 event was observed to be equitably distributed with magnetic activity over the Kp = 2- to 4 range at all the three stations with the peak event recorded at Kp = 3-. The magnitude of duration of Pc4 event diminished in the station order PON, HAN and NAG respectively. The prominent peaks in the seasonal Pc4 event were found at Kp = 3-, 3 for all the seasons. However additional pinnacles were seen at Kp = 1-, 1 and 1+ for the autumn season. It is additionally important that Pc4 in winter was found during extreme magnetic activity when 5+ < Kp < 8+
In the current examination, the outcomes are in agreement with recommendations of Takahashi
In conclusion, it has been demonstrated that the occurrence of Pc4 pulsations depends on solar wind velocity with a threshold at about 250 km/s and ranging up to 950 km/s. It is likely that an instability originating from the direct interaction between the solar wind and the magnetosphere is exciting Pc4 pulsations through bow-shock associated waves.
The authors are thankful to the Director, Indian Institute of Geomagnetism (IIG) Navi Mumbai, India for kindly providing Pc4 pulsations data.