Browsing by Author "Bhattacharyya, Archana"
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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.Item Restricted Recent advances in equatorial, low- and mid-latitude aeronomy(Elsevier, 2013-10) Bhattacharyya, Archana; Chau Chong Shing, Jorge Luis; Denardini, Clezio M.; Hysell, David L.; Makela, Jonathan J.; Shiokawa, Kazuo; Kudeki, ErhanThis special issue of the Journal of Atmospheric and Solar–Terrestrial Physics on “Recent Advances in Equatorial, Low- and Mid-latitude Aeronomy” contains selected papers presented at the 13th International Symposium on Equatorial Aeronomy (ISEA13). This symposium is the latest in a long series of ISEAs, which was started in 1962 soon after the Jicamarca Radio Observatory (JRO) began its operation near Lima, Peru. The first ISEA was held in Huaychulo, Peru; and since then the symposium has been held every 3–5 years at different locations around the globe, bringing together scientists from all over the world, who are interested in the low- and mid-latitude atmosphere and ionosphere, and their coupling to other latitudes and altitudes. The ISEAs have become important events for researchers working in this field, as it offers them an opportunity to share their most recent results and discuss new techniques and possibilities for future coordinated campaigns and experiments.Item Restricted Relating the interplanetary-induced electric fields with the low-latitude zonal electric fields under geomagnetically disturbed conditions(American Geophysical Union, 2013-03-21) Anghel, Adela; Anderson, David; Chau Chong Shing, Jorge Luis; Yumoto, Kiyohumi; Bhattacharyya, ArchanaThe overall ionospheric variability with periods ranging from long-term, secular changes to days, hours, and even minutes and seconds, is influenced by the solar activity, geomagnetic activity, and processes originating in the lower atmospheric layers. Using a wavelet transform approach, in this paper, we study the short-term (minutes to hours) and day-to-day variability of the ionospheric low-latitude zonal electric fields (LLZEF) at three longitude sectors, Peruvian, Philippine, and Indian, during time intervals of increased geomagnetic activity and relate the LLZEF variability to changes in the dawn-to-dusk component of the interplanetary electric field (IEF). Continuous Morlet wavelet and cross-wavelet amplitude spectra with reduced and increased frequency resolutions were obtained to analyze and compare the oscillation activity in the LLZEF and IEF spectra, in the 10-min to 10-h and 1.25- to 12-d period ranges. For the 1.25- to 12-d period range, periodicities in the LLZEF spectrum were compared with similar periodicities in the IEF spectrum over 9 February to 9 June 2001, with our wavelet results indicating the geomagnetic activity as an important driver of LLZEF variability in this period range. For the 10-min to 10-h period range, four case studies were examined when concurrent observations of Jicamarca incoherent scatter radar zonal electric field and IEF, as calculated from the ACE satellite solar wind velocity and interplanetary magnetic field data, were available. We show that the wavelet transform represents a powerful tool to study the frequency dependence of the two specific mechanisms of ionospheric electric field variability, which are dominant during geomagnetic storms, namely penetration and disturbance dynamo.Item Restricted Role of IMF By in the prompt electric field disturbances over equatorial ionosphere during a space weather event(American Geophysical Union, 2017-02-04) Chakrabarty, D.; Hui, Debrup; Rout, Diptiranjan; Sekar, R.; Bhattacharyya, Archana; Reeves, G. D.; Ruohoniemi, J. M.On 7 January 2005 (Ap=40) prompt penetration electric field perturbations of opposite polarities were observed over Thumba and Jicamarca on a few occasions during 13:45–16:30 UT. However, the electric field was found to be eastward during 14:45–15:30 UT over both Thumba and Jicamarca contrary to the general expectation wherein opposite polarities are expected at nearly antipodal points. On closer scrutiny, three important observational features are noticed during 14:10–15:15 UT. First, during 14:10–14:45 UT, despite increasing southward interplanetary magnetic field (IMF) Bz condition, the already westward electric field over Thumba weakened (less westward) while the eastward electric field over Jicamarca intensified (more eastward). Second, the electric field not only became anomalously eastward over Thumba but also got intensified further during 14:45–15:00 UT similar to Jicamarca. Third, during 15:00–15:15 UT, despite IMF Bz remaining steadily southward, the eastward electric field continued to intensify over Thumba but weakened over Jicamarca. It is suggested that the changes in IMF By component under southward IMF Bz condition are responsible for skewing the ionospheric equipotential patterns over the dip equator in such a way that Thumba came into the same DP2 cell as that of Jicamarca leading to anomalous electric field variations. Magnetic field measurements along the Indian and Jicamarca longitude sectors and changes in high‐latitude ionospheric convection patterns provide credence to this proposition. Thus, the present investigation shows that the variations in IMF By are fundamentally important to understand the prompt penetration effects over low latitudes.