Comparative study of the equatorial ionosphere over Jicamarca during recent two solar minima

摘要

It is a critical issue that whether or not the extremely deep solar minimum of solar cycle 23/24 brought serious influences on the Earth's space environment. In this study, we collected and manually scaled the ionograms recorded by a DPS ionosonde at Jicamarca (12.0°S, 283.2°E) to retrieve F layer parameters and electron density (A 1 e) profiles.A comparative study is performed to evaluate the equatorial ionosphere in solar minima of cycle 22/23 (1996-1997) and 23/24 (2008-2009). The seasonal median values of the critical frequency of F_2 layer (f0F_2) were remarkably reduced in four seasons during the deep solar minimum, compared to those in 1996-1997. It is the first time to find that lower values prevail at most times in 2008-2009 in the F_2 layer peak height (hm F_2) and Chapman scale height (Hm). The bottomside profile thickness (BO) shows higher values in 2008-2009 than that in 1996-1997 at some daytime intervals, although it also becomes smaller during the rest times. Furthermore, the ionosphere in 2008-2009 is contracted strongly at altitudes above hmF_2 and more perceptible in the afternoon hours. The decrease in Ne is strongest in September equinox and weakest in June solstice. The ionospheric responses from solar minimum to minimum are mainly caused by the reduction in solar extreme ultraviolet intensity, and the contribution from dynamical processes competes and is variable. Analysis reveals that semiannual and longer-scale components are certainly reduced during the deep solar minimum, while shorter scale (e.g., 4 month) components may disrupt the decline picture at some times.