Study of structures of the sporadic E layer by using dense GNSS network observations

Ionogram observed at Kokubunji, Japan, at 05:00 UT on June 4, 2018

(Top): The maximum frequency reflected by the Es layer (ftEs) and the minimum frequency that can pass through the Es layer (fbEs) manually scaled from ionograms at Kokubunji; (Middle): the difference between ftEs and fbEs; and (Bottom): the maximum ROTI value over the ionosonde (Tokyo) within the radius of 100 km). All the data were collected on June 4, 2018

ROTI map at 05:00 UT on June 4, 2018; the red solid line shows the front identified by HT

ROTI map at 05:15 UT on June 4, 2018, with a front identified by the Hough transform (red solid line); the identified front at 05:00 UT is shown by a red broken line

IPP traces of six receiver-satellite pairs with large ROTI values from 04:45 to 05:30 UT; the legend indicates the pairs of the receiver and satellite connected by “/”; arrows show the direction of IPP motion. The Es layer frontal structures identified by the Hough transform at 05:00 and 05:15 are also shown by red broken lines; locations of the receivers are indicated by black crosses.

Temporal variation of the slant TEC values for the six satellite-receiver pairs shown in Figure 6. Each legend indicates the corresponding pairs of the receiver and satellite connected by “/.” Vertical arrows indicate the TEC perturbation causing ROTI enhancements (for the receiver 0630 and satellite PRN27, TEC values before 4.95 hours which are smooth have been omitted).

Illustration of the vertical cross-section of the Es front with a steeper density gradient on the backside than the frontside