Effect of interplanetary conditions and auroral activity on intermittency regularities of Pi3 irregular geomagnetic pulsations

Earlier we showed that the cumulative distribution function (CDF) of the burst amplitudes of Pi3 irregular geomagnetic pulsations observed during the development of substorms in the night sector of the magnetosphere follows the power law f (A) = A^-a, where A is the amplitude of the bursts, a is the exponent. We considered the exponent α, which characterizes the CDF slope, as a characteristic of the intermittency and state of the medium in which Pi3 bursts are formed. In this work are presented the results of study of the effect of the Bz component direction of the interplanetary magnetic field (IMF), auroral activity and b plasma parameter (equal to the ratio of thermal pressure to magnetic pressure) reflecting solar wind turbulence on the intermittency regularities of the Pi3 pulsation bursts. One-minute digital observations of the magnetic field from two observatories in the Arctic and Antarctic: Heiss Island (HIS, corrected geomagnetic coordinates Latitude 74.80°, Longitude 144.46°) and Mirny (MIR, corrected geomagnetic coordinates Latitude –76.93°, Longitude 122.92°) from the World Data Center for Solar-Terrestrial Physics (Moscow) (http://www.wdcb .ru/stp/data/geo_min.val/) were used. Hourly average parameters of the interplanetary medium and auroral activity (AE-index) were obtained from the OMNI 2 database (http://omniweb.gsfc.nasa.gov/ow.html). A total of 305 and 415 Pi3 pulsation bursts were analyzed in HIS and MIR, respectively. Taking into account interplanetary conditions, all Pi3 events at each of the observatories were divided into two clusters depending on the direction of the IMF Bz component: Pi3 bursts observed at Bz<0 and Bz>0. In a similar way, all cases were divided into two clusters according to the value of the AE index: Pi3 bursts observed at AE <500 nT and AE >500 nT. According to the value of the b parameter, the events were divided into Pi3, observed at 0<β≤1.3 (solar wind plasma is highly turbulized) and β>1.3 (weakly turbulized). For each group, a separate study of the CDF character of the Pi3 pulsation amplitudes was performed and estimates of the power-law exponent a were obtained. It has been revealed that the bursts of Pi3 pulsations observed in HIS and MIR are excited in a highly turbulent medium (the value of the exponent α > 1). Regardless of the parameters considered (Bz, AE and β), in MIR the value of exponent α is significantly larger than HIS. For example, at Bz<0 and Bz>0 the value of α in HIS is 1.50 and 2.47, and in MIR 3.04 and 3.26, respectively. Similarly, at AE <500 nT and AE>500 nT, the α exponent in HIS is 1.60 and 1.52, in MIR 2.81 and 2.63, respectively. The distributions of Pi3 burst amplitudes as a function of the parameter β (at 0<β≤1.3 and β>1.3) were also approximated by power functions with lower α exponents in HIS (1.44 and 1.65) compared to MIR (2.60 and 2.74). It should be noted that similar trends are observed in the behavior of the exponent α in the northern and southern hemispheres when dividing Pi3 bursts into clusters according to the values of Bz, AE and β. So, the value of the exponent α in both HIS and MIR is greater at Bz>0, AE <500 nT and β>1.3 than at Bz<0, AE>500 and 0<β≤1.3. Thus, from the obtained results it follows that the level of turbulence in the region of excitation of Pi3 pulsations (presumably in the magnetotail) is significantly higher in the absence of disturbances in the solar wind plasma, relatively moderate auroral activity and weak solar wind turbulence.