Some Differences in the Dynamics of the Intermediate Descending Layers Observed During Periods of Maximum and Minimum Solar Flux

Abstract

In this paper, ionograms from São Luís (SL, 2°S; 44°W, I: −3.8°) and Cachoeira Paulista (CP, 22.42°S; 45°W, I: −34.4°) are analyzed to examine the characteristics of the intermediate descending layers (ILs) over the Brazilian equatorial and low-latitude regions under different solar flux conditions. The solar flux effects on the ILs are investigated in terms of the rate of occurrence of the IL; the seasonal behavior of some parameters such as the height, frequency, and velocity; and the duration and the number of ILs events observed per day. One of the main results of this work is that unlike over CP, the ILs over SL presented some peculiarities, such as a lower rate of occurrence during a period of solar maximum activity (2003) when compared with a period of solar minimum activity (2009). This apparent variation was likely caused by the magnetic equator moving away from SL during this period. The duration of the ILs was also investigated, and it was found that in 2009, the ILs presented higher life time than in 2003. The descending velocity of the ILs is compatible with the semidiurnal and quarter-diurnal tides. Over SL, the larger descending rate in some cases (>10 km/hr) may reveal the additional influence of the gravity waves in the IL's dynamics. Recently, Dos Santos et al. (2019) presented a climatological study of the ILs over the equatorial and low-latitude regions in Brazil during a period of extreme solar minimum activity. They found an ILs' rate of occurrence higher than 90% over the low-latitude sector and higher than 60% over the equator. The day-today variability observed in the ILs parameters such as the height, frequency of occurrence, and descent velocity may result from variations of tides, the electric fields, the metallic ion, or due to the influences of gravity waves (

F Region Electric Field Effects on the Intermediate Layer Dynamics During the Evening Prereversal Enhancement at Equatorial Region Over Brazil

“…We believe that there must be a height limit between the E and F regions within which the IL can respond to the electric fields of the F region, more specifically to the PRE, and that this limit should vary between ∼ 160 and 170 km. The results presented by A. M. Santos et al (2020) reinforce this assumption since in 2003, the period in which most of the ascending ILs were observed, the tendency was that the layers located a little lower than this limit presented a movement that was downward (as the example of Figure 1 in this present work) and not upward as reported here. In 2009, almost all the ILs near the sunset times were already located at altitudes equal to or less than 130 km.…”

“…A. M. Santos et al (2020) reported that the probability of an IL to occur near or after ∼18:00 LT is quite small. Around this time, they showed that the average values of virtual height of the ILs over SL during 2003 are located at altitudes close to 160 km or below.…”

“…As will be shown in the present work, the ILs can be influenced by the evening enhancement in the zonal electric field. Dos Santos et al (2019) and A. M. Santos et al (2020) studied the behavior of the ILs over the Brazilian equatorial and low latitude regions of São Luís (SL) and Cachoeira Paulista (CP), respectively, during periods of maximum ( 2003) and minimum ( 2009) solar activity. In summary, it was found that: (1) the IL's occurrence rate over both regions is high; the occurrence in SL was higher in 2009 (I = −3.8°) than in 2003 (I = −1.6°), indicating a possible dependence with the magnetic inclination angle (I); (2) the ILs' occurrence rate appears to be independent (or weakly dependent) on the solar activity condition; (3) the dynamic of the ILs can be influenced by atmospheric tides, gravity waves and electric fields; (4) the ILs occur predominantly during daytime and present a well-defined downward movement; however nocturnal and ascending ILs also can be observed over the Brazilian region; (5) depending upon the height of its formation, the ILs can descend and merge with the normal Es layers; (6) the IL's lifetime is longer in solar minimum period (both over SL and CP), with shorter life time over the equator (SL) independently of the solar activity ; and (7) the descending rate of the ILs over SL and CP seems to be compatible with that of the semidiurnal and quarter-diurnal tides.…”

Comment on angeo-2021-52

“…Additionally, they observed that the probability of formation of an IL when the minimum virtual height of the F2 layer is above 220 km is very low, but it can increase during magnetically disturbed periods. As shown by Santos et al (2020), the ILs' occurrence over Cachoeira Paulista (22.42° S; 45° W) was very high both in 2009 (a low solar activity year and the same period of this report) and 2003 (a high solar activity year). These results show that in general, the ILs occurrence resulted to be independent of the magnetic disturbances, since the referred two periods of geomagnetic activity are totally different from each other.…”

“…Recently, dos Santos et al (2019) and Santos et al (2020; have studied the essential characteristics of the ILs over the Brazilian sector during the minimum and the maximum solar activity epochs and observed that these layers are predominantly diurnal and present a typical downward movement that can last from minutes to hours. Depending on the height at which the ILs are formed, they can descend and merge with the normal ongoing sporadic -E (Es) layers.…”