Generation of Non‐Substorm Pi2s at Low and Middle Latitudes

Abstract

AbstractThis study analyzes the characteristics of non‐substorm Pi2 (impulsive pulsations [3–25 mHz]) from low and middle latitudes and investigates the trends of these oscillations. Pi2 events are identified from geomagnetic H‐component data from low and middle latitude observatories Hyderabad (HYB, L = 1.03) and Paratunka (PET, L = 2.1) respectively, during solar maximum period (2015–2016) for quietest geomagnetic conditions, with stringent criteria of interplanetary parameters and activity indices. Data from five high‐latitude stations from THEMIS ground magnetometer chain, covering all local time sectors are additionally analyzed to verify the absence of substorms, pseudo substorms, etc. which may also generate Pi2 signatures. Variation of non‐substorm Pi2 periods with geomagnetic activity index Kp and solar wind speed (Vsw) show inverse relations with Pi2 period at HYB. In addition, non‐substorm Pi2s are distributed equally in all local time sectors with ratio of second harmonic to fundamental Pi2 ranging within 1.3–2.2. These trends of non‐substorm Pi2s indicate plasmaspheric cavity resonance (PCR) as the dominant source at low latitude, confirmed using a theoretical model. In contrast, non‐substorm Pi2 periods do not show a steady trend with Kp and Vsw at midlatitude station PET. Local time variations show an increased period in the premidnight sector at PET. A close agreement between theoretical estimates and observed periods of non‐substorm Pi2‐s at PET, leads to the inference of Alfvenic nature of these modes, attributable to a resonant oscillation.