Browsing by Author "Maruyama, Naomi"
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Item Restricted A new source of the midlatitude ionospheric peak density structure revealed by a new Ionosphere‐Plasmasphere model(American Geophysical Union, 2016-02-02) Maruyama, Naomi; Sun, Yang-Yi; Richards, Phillip G.; Middlecoff, Jacques; Fang, Tzu-Wei; Fuller-Rowell, Timothy J.; Akmaev, Rashid A.; Liu, Jaun-Yeng; Valladares, Cesar E.The newly developed Ionosphere‐Plasmasphere (IP) model has revealed neutral winds as a primary source of the “third‐peak” density structure in the daytime global ionosphere that has been observed by the low‐latitude ionospheric sensor network GPS total electron content measurements over South America. This third peak is located near −30° magnetic latitude and is clearly separate from the conventional twin equatorial ionization anomaly peaks. The IP model reproduces the global electron density structure as observed by the FORMOSAT‐3/COSMIC mission. The model reveals that the third peak is mainly created by the prevailing neutral meridional wind, which flows from the summer hemisphere to the winter hemisphere lifting the plasma along magnetic field lines to higher altitudes where recombination is slower. The same prevailing wind that increases the midlatitude density decreases the low‐latitude density in the summer hemisphere by counteracting the equatorial fountain flow. The longitudinal variation of the three‐peak structure is explained by the displacement between the geographic and geomagnetic equators.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 Penetration electric fields: Efficiency and characteristic time scale(Elsevier, 2007-07) Huang, Chao-Song; Sazykin, Stanislav; Chau Chong Shing, Jorge Luis; Maruyama, Naomi; Kelley, Michael C.Penetration of the interplanetary electric field (IEF) to the middle- and low-latitude ionosphere has been investigated for nearly four decades. Most previous studies focused on the correlation between the interplanetary and ionospheric electric field perturbations. Very little attention has been paid to a quantitative relationship except for a recent case analysis by Kelley et al. [2003. Penetration of the solar wind electric field into the magnetosphere/ionosphere system. Geophysical Research Letters 30(4), 1158. doi:10.1029/2002GL016321]. In this paper, we present a statistical result of the efficiency of IEF penetration to the dayside equatorial ionosphere; the efficiency is defined as the ratio of the change of the equatorial ionospheric electric field to the change of the IEF. The Jicamarca incoherent scatter radar has made continuous operation with a coherent scatter mode since 2001, and the radar data of equatorial ionospheric electric fields are used in our statistics. On the basis of data statistics, we derive an empirical value of 9.6% for the efficiency of penetration. We apply this empirical formula to the observations and numerical simulations of storm-time penetration electric fields over a prolonged interval of southward interplanetary magnetic field. The prediction of the formula is in good agreement with case studies and with results from first-principle simulations of the coupled magnetosphere–ionosphere–thermosphere system. We conclude that the IEF can continuously penetrate to the low-latitude ionosphere without significant attenuation for many hours during the main phase of magnetic storms.