Two-dimensional observations of midlatitude sporadicEirregularities with a dense GPS array in Japan

Abstract

[1] We observed two-dimensional structure and time evolution of ionospheric irregularities caused by midlatitude sporadic E (E s ) over Japan as positive anomalies of total electron content (TEC) by analyzing the data from the nationwide Global Positioning System (GPS) array. In this paper we report a case study of strong E s observed in the local evening of 21 May 2010, over Tokyo, Japan. In the slant TEC time series, E s showed a characteristic pulse-like enhancement of~1.5 TEC units lasting for~10 min. We plotted these positive TEC anomalies on the subionospheric points of station-satellite pairs to study the horizontal structure of the E s irregularity. We confirmed that the irregularity existed at the height of 106 km by comparing the data of multiple GPS satellites, which is consistent with the local ionosonde observations. The horizontal shapes of the E s irregularity showed frontal structures elongated in E-W, spanning~150 km in length and~30 km in width, composed of small patches. The frontal structure appears to consist of at least two parts propagating in different directions: one moved eastward by~60 m s À1 , and the other moved southwestward by~80 m s À1 . Similar TEC signatures of E s were detected by other GPS satellites, except one satellite that had line of sight in the N-S direction which dips by 40-50°toward north, which indicates the direction of plasma transportation responsible for the E s formation. We also present a few additional observation results of strong E s irregularities.Citation: Maeda, J., and K. Heki (2014), Two-dimensional observations of midlatitude sporadic E irregularities with a dense GPS array in Japan, Radio Sci., 49, 28-35,

Morphology and dynamics of daytime mid-latitude sporadic-E patches revealed by GPS total electron content observations in Japan

“…We calculated the phase differences between L1 and L2 expressed in length, with which we can monitor changes of TEC along the line of sight (LOS); this is called slant TEC (STEC). In STEC time series, Es patches are recognized as short positive pulses (Maeda and Heki 2014). They are clearly recognizable during daytime (Fig.…”

“…It causes extra ionospheric delays of microwaves and can be detected with TEC observations with dual-frequency GNSS receivers (Maeda and Heki 2014). In this study, we analyzed the data from the GNSS Earth Observation Network (GEONET), composed of~1200 continuously operating receivers in Japan.…”

“…Liu et al (2014) suggested that strong winds and wind shears are produced by the nonlinear interactions between gravity waves and tidal backgrounds. Maeda and Heki (2014) reported the fragmentation of frontal structure associated with MSTID passage, i.e., E-W-elongated Es patches dissolved into smaller wave-like pieces aligned in NW-SE. The horizontal separation of the pieces is~40 km, and they moved southwestward by~80 m/s in the local evening.…”

“…The patch had a horizontal dimension of 30 × 10 km and showed elongation in NW-SE. Recently, Maeda and Heki (2014) succeeded in the 2-D imaging of daytime mid-latitude Es with total electron content (TEC) observations from a dense network of GPS receivers in Japan. They showed several images of clear frontal structures extending in E-W over 100 km.…”

3D tomography of midlatitude sporadic-E in Japan from GNSS-TEC data

“…It occurs in low-latitude (Jayachandran et al 1999;Resende and Denardini 2012), midlatitude (Wakabayashi et al 2005;Maeda and Heki 2014), and high-latitude (Kirkwood and Nilsson 2000) regions and is widely believed to be generated by the vertical shear of zonal winds (Whitehead 1970(Whitehead , 1989. There have been studies on Es over decades to clarify its generation mechanism, structure, time evolution, and distribution using various instruments and techniques.…”