Statistics of High Latitude Sporadic E Layer Occurrence derived using
Incoherent Scatter Radar Observations
Abstract
Sporadic-E (Es) layers are characterized as thin layers (1-5 km) of
enhanced electron density that occur between 90-120 km in altitude.
Sporadic E at mid- and low-latitudes has a reasonably well established
climatology, while at high latitudes there have been fewer
investigations that have characterized the climatology of sporadic E
occurrence using altitude resolved measurements. Incoherent scatter
radar provides direct altitude resolved measurements of the E-region
ionosphere with relatively high altitude resolution. Since 2008, the
Poker Flat Incoherent Scatter Radar (PFISR) has been operating in nearly
continuous operations through a low duty cycle mode, thus enabling
observations of sporadic E. The distinction between Es and auroral
precipitation is detectable and is generally associated with the
differences in structure height with Es being on average smaller in
altitudinal range and shorter time duration. The purpose of this
investigation is to present observations of sporadic E derived from this
nearly continuous database of alternating code and Barker code PFISR
data spanning the years from 2007-2021. We visually identified the
sporadic E layers and have found approximately 300 events. We present
statistical results of the occurrence, duration, and characteristics of
high latitude sporadic E derived from these events. The preponderance of
events manifested within 95 to 120 km, typically lasted 1 to 3 hours,
and mostly occurred during May through September with observance peaking
in July. In addition, the trends indicated a potential disconnect
between sporadic-E events and auroral activity, which was previously
considered the primary driving force behind high latitude sporadic-E
events. The climatology of high latitude sporadic E is an important
contribution that must be considered in future high latitude models of
the ionosphere.