Browsing by Author "Alex, S."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Restricted Can a nightside geomagnetic Delta H observed at the equator manifest a penetration electric field?(American Geophysical Union, 2013-02-12) Wei, Y.; Fraenz, M.; Dubinin, E.; He, M.; Ren, Z.; Zhao, B.; Liu, J.; Wan, W.; Yumoto, K.; Watari, S.; Alex, S.A prompt penetration electric field (PPEF) usually manifests itself in the form of an equatorial ionospheric electric field being in correlation with a solar wind electric field. Due to the strong Cowling conductivity, a PPEF on the dayside can be inferred from Delta H (ΔH), which is the difference in the magnitudes of the horizontal (H) component between a magnetometer at the magnetic equator and one off the equator. This paper aims to investigate the performance of ΔH in response to a PPEF on the nightside, where the Cowling conductivity is not significant. We first examine the strongest geomagnetically active time during the 20 November 2003 superstorm when the Dst drops to −473 nT and show that the nightside ΔH can indeed manifest a PPEF but with local time dependence and longitude dependence. We then examine a moderately active time by taking advantage of the multiple‐penetration event during 11–16 November 2003 when the Dst remains greater than −60 nT. During this event, a series of PPEF pulses recorded in Peru, Japan, and India form a database, allowing us to examine PPEF effects at different local times and longitudes. The results show that (1) the nightside ΔH was caused by attenuation of the effects of the polar electric field with decreasing latitude; (2) the nightside ΔH can manifest a PPEF at least in the midnight‐dawn sector (0000–0500 LT), but not always; and (3) the magnitude of the nightside ΔH in the midnight‐dawn sector in Peru is on average only 1/18 of that of the dayside ΔH in response to a given PPEF.Item Restricted Interplanetary electric fields and their relationship to low-latitude electric fields under quiet and disturbed conditions(Elsevier, 2007-07) Anghel, Adela; Anderson, David; Maruyama, Naomi; Chau Chong Shing, Jorge Luis; Yumoto, Kiyo; Bhattacharyya, Archana; Alex, S.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.