Speaker
Description
The diurnal variation of plasma density in the ionosphere is largely characterized by a single peak
around local noon. However, diurnal double maxima (DDM) is sometimes observed when two
distinct peaks and one valley in plasma density appear during the local daytime. Understanding
DDM structures is essential for studying ionospheric dynamics and their key drivers, including
neutral winds, E ×B drift, and solar irradiation, as these variations impact radio wave propagation
and space weather forecasting. This study investigates DDM occurrences using ionosonde
observations from stations in Hermanus (34.4◦S, 19.2◦E, magnetic latitude: 42.08◦S) and Grahamstown
(33.3◦S, 26.5◦E, magnetic latitude: 41.06◦S) during solar cycle 24 (2008–2019). A robust automated
algorithm was developed to detect DDMs based on the presence of two fully formed peaks
separated by a depletion (valley), all occurring between local sunrise and sunset. The algorithm
established the criteria using a minimum peak-to-valley ratio of at least 6% to ensure significant
peak prominence, a minimum peak-to-peak interval of 40 minutes to capture the time difference
between two peaks, and an extra peak prominence threshold not exceeding 5% to filter out additional
peaks. These thresholds ensure that only well-defined DDM structures are identified. The
method was validated through visual inspection, achieving a detection accuracy of 97%. Using
this approach, we identified 1,532 and 1,270 DDM events at Hermanus and Grahamstown from a
total of 3,534 and 2,835 observation days, respectively, over the whole solar cycle. This translated
to an occurrence rate of 43% at Hermanus and 45% at Grahamstown. We will explore statistical
trends in terms of seasonal and solar cycle variations for each ionosonde station. Comparing and
contrasting the trends between the stations may provide indications about possible mechanisms
influencing DDM development. Furthermore, we will explore whether there are DDMs that are
common between the two stations, as this may indicate the scale size and/or propagation of these
events.
