Interplanetary electric fields and their relationship to low-latitude electric fields under disturbed conditions

Abstract

Recent studies have demonstrated that ground-based magnetometer observations can be used to infer realistic, daytime vertical E×B drift velocities in the Peruvian and Philippine longitude sectors. It has also been demonstrated that under certain conditions the time variability in the interplanetary electric field (IEF)—minutes to hours—is reflected in the daytime, prompt penetration of high-latitude electric fields to low latitudes. In this paper, we incorporate magnetometer-inferred E×B drift techniques to extend this study to include the Indian sector E×B drift velocities and to investigate the relationships between IEF conditions and daytime, low-latitude electric field observations under both geomagnetically quiet and disturbed conditions. This paper addresses several basic questions related to the relationships between IEF conditions and low-latitude east–west electric fields. (1) When low-latitude electric fields exhibit quiet-time, Sq-type behavior, what are the IEF conditions? (2) Under disturbed conditions, what are the relationships between the IEF parameters and the low-latitude electric fields in the Peruvian, Philippine, and Indian longitude sectors? (3) If the three longitude sector electric field responses are similar under disturbed conditions, is the response consistent with the current ideas put forward at the Millstone Hill Workshop on promptly penetrating electric fields and over-shielding effects at low latitudes? We address the above questions by analyzing magnetometer-inferred E×B drift velocities between January 2001 and December 2004 when there exists more than 500 quiet days and more than 235 geomagnetically disturbed days, defined by daily Ap values greater than 20. It is suggested that the neural network approach that provides realistic E×B drift velocities based on magnetometer observations can be applied at any longitude where appropriately placed magnetometers exist. It is found that: (1) the average quiet, daytime upward E×B drift velocity vs. LT in the Indian sector is comparable to the average velocity vs. LT in the Peruvian sector and both are roughly 3–5 m/s less than the values in the Philippine sector; (2) under quiet conditions, the peak velocity occurs at 1100 LT in the Peruvian sector and at 1000 LT in both the Philippine and Indian sectors; and (3) during disturbed conditions, it is observed that daytime, promptly penetrating electric fields occur, simultaneously, in the Philippine, Indian and Peruvian sectors, in response to fluctuating IEF conditions.