Imaging the midlatitude sporadic E plasma patches with a coordinated observation of spaceborne InSAR and GPS total electron content

Abstract

Kilometer‐scale fine structures of midlatitude sporadic E (Es) plasma patches have been directly imaged for the first time by an interferogram derived from L band Advanced Land Observation Satellite/Phased Array‐type L band Synthetic Aperture Radar data obtained over southwestern Japan. The synthetic aperture radar interferogram captured the eastern part of a large‐scale frontal structure of daytime midlatitude Es which spans over 250 km in the east‐northeast to west‐southwest direction. Fine structures are characterized by frontal and disc‐shaped patches which are elongated in the same direction as the large‐scale frontal structure. Length and width of the disc‐shaped patches are 10–20 km and 5–10 km, respectively, and they are quasi‐periodically located with a typical separation of 10–15 km. The Kelvin‐Helmholtz instability with the vertical shear of zonal winds is considered to be the most likely candidate for the generation mechanism of the frontal patch and disc‐shaped patches aligned in the zonal direction.

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

“…TEC corresponds to the number of electrons integrated along the line of sight (LoS) of GNSS microwave signals between satellite and ground receivers. Maeda et al (2016) and Furuya et al (2017) used an interferometric synthetic aperture radar (InSAR) to draw detailed 2D maps of Es patches.…”

Midlatitude sporadic-E episodes viewed by L-band split-spectrum InSAR

“…Another advantage of InSAR imaging is that no receivers have to be deployed on the imaging area, whereas the temporal resolution of InSAR is seriously limited by the satellite's recurrence interval, which is 46 days in the case of ALOS/PALSAR. Maeda et al (2016) attributed the phase anomalies in the InSAR image to the Es episode, given the nearly identical location of the phase anomalies in the InSAR data and those derived from the GNSS TEC data. We should note, however, that GNSS TEC is physically distinct from the InSAR phase anomaly, because the InSAR phase includes the dispersive signal due to TEC and the nondispersive phase delay that has been mostly attributed to polar molecules in the troposphere.…”

“…Our first objective is to report the results of our application of the SSM to two Es episodes in Japan: the first episode is the one reported by Maeda et al (2016), and the second one is a new Es episode detected by ALOS2/ PALSAR2 launched in 2014, a follow-on mission of JAXA's ALOS/PALSAR. The second objective is to examine the impact of higher-order terms in the refractive index on the estimates of dispersive signals, which is motivated by the results based only on the conventional first-order refraction index.…”

“…In terms of the spatial resolution in the observation of Es, however, satellite-based InSAR imaging is more advantageous than the GNSS network. Maeda et al (2016) first succeeded in demonstrating an Es episode in Japan using both GNSS TEC and an InSAR image derived from the Advanced Land Observation Satellite/Phased Array L-band Synthetic Aperture Radar (ALOS/PALSAR). ALOS was launched in 2006 by the Japan Aerospace Exploration Agency (JAXA).…”

Detections and simulations of tropospheric water vapor fluctuations due to trapped lee waves by ALOS-2/PALSAR-2 ScanSAR interferometry

“…4a. Besides, ionospheric effects in InSAR usually have spatial scale of more than a hundred of kilometers (Kinoshita et al 2013) and around 20 km with a patchy shape in cases of sporadic-E events (Maeda et al 2016). Therefore, we also assumed that the phase variation in Fig.…”