Cachoeira Paulista Research Articles

Analysis of the different physical mechanisms in the atypical sporadic E (Es) layer occurrence over a low latitude region in the Brazilian sector

We present a study about the atypical and spreading Sporadic E-layers (Es) observed in Digisonde data. We analyzed a set of days around space weather events from 2016 to 2018 over Cachoeira Paulista (CXP, 22.41°S, 45°W, dip ∼35°), a low-latitude Brazilian station. The inhomogeneous Es layer is associated with the auroral-type Es layer (Esa) occurrence in this region due to the presence of South American Magnetic Anomaly (SAMA). However, we also observe that the spreading Es layers occurred days before the magnetic storms or quiet times. Also, this specific type of Es layer has some different characteristics concerning the Esa layer. We used data from the imager, satellite, and meteor radar to understand the dynamic processes acting in this Es layer formation. Our results lead us to believe that other mechanisms affect the Es layer development. We show evidence that the instabilities added to the wind shear mechanism can cause the atypical Es layers, such as Kelvin-Helmholtz instability (KHI). Finally, an important discovery of this work is that the spreading Es layer, mainly during quiet times, is not necessarily due to the particle precipitation due to the SAMA. We found that the wind shear can be turbulent, influencing the Es layer development. Lastly, our analysis better understood the Es layer behavior during quiet and disturbed times.

ASSESSMENT OF FIRE RISK IN THE VALE DO PARAÍBA REGION, SOUTHEAST ATLANTIC RAINFOREST, BRAZIL

In recent times, the area burned by wildfires in the Atlantic Rainforest, a biodiversity hotspot, has increased and its occurrence may threaten this biome. The objective of this study was to evaluate the performance of three fire risk indices for a historical time series in Vale do Paraíba Paulista, southeast Atlantic Rainforest, Brazil. Daily meteorological data from automatic weather stations and hotspots records from INPE fire monitoring program were used to validate the formulas. Three fire risk indices were calculated: Angstron, Monte Alegre Formula (MAF) and Telecyn. We expected that we would find an increase in fire risk in recent years in the region, which we found for some municipalities, and that burning risk would be higher in dry months, which we showed. Moreover, we argued that protected areas surrounding higher fire risk sites are being threatened, especially near São Luiz do Paraitinga and Taubaté. Lastly, considering the higher probability in detecting fire risk in higher classes, Angstron was the most adequate for Campos do Jordão and MAF for Sao Luiz do Paraitinga, Taubaté and Cachoeira Paulista.

Latitudinal responses of the ionosphere over South America during HILDCAA intervals: Case studies

Aspects regarding the influence of High-Intensity Long-Duration Continuous Auroral Electrojet Activity (HILDCAA) intervals on ionospheric dynamics have been objecting to increasing interest in the last years. Notwithstanding, some key interconnections between the HILDCAA intervals impacts on the ionosphere over distinct latitudes, according to the solar cycle phase, remain to require further investigation. In this work, the F2 layer peak height and its critical frequency (hmF2 and foF2, respectively) from Digisonde data obtained over São Luís (2.60° S; 44.21° W), Cachoeira Paulista (22.70° S; 44.98° W), and Port Stanley (51.60° S, 57.9° W), were evaluated to unravel more details of the ionospheric responses to four HILDCAA intervals as case studies. Those are equatorial, low, and mid-latitude stations, respectively, and the main results over them presented a similar trend in terms of solar cycle dependence, with the greater impact on the ionospheric density along with solar maximum conditions, despite the higher frequency of HILDCAA occurrences in the descending and minimum phases. The variation of hmF2 due to HILDCAA effects in comparison to quiet time is about 20% in equatorial and mid-latitudes, while over the low latitude station the hmF2 ranges positively up to 40%. These results enhance our understanding of the HILDCAAs magnitude degree both regarding its solar cycle occurrence, and its effects in different ionospheric latitudinal sections.

Storm-time variability of ionospheric irregularities over South America

The generation and development of ionospheric irregularities is an important topic of study in space weather, mainly because of their adverse effects on navigation and positioning systems, as well as in trans-ionospheric communications. To improve our prediction capabilities, it is necessary to better understand their variabilities during different geomagnetic conditions. The purpose of this research is to analyse the occurrence characteristics of ionospheric irregularities over South America during geomagnetic storms. Using data from six ionosondes and GPS stations in Brazil and Perú, observations from the JULIA radar and Swarm in situ electron density measurements, we examined the presence of irregularities during three intense storms (October 12, 2016, October 7, 2015 and August 25, 2018). Our data show that during the geomagnetic storms that occurred in October 2016 and October 2015, in the Brazilian region, the generation of ionospheric irregularities was usually inhibited during the storm recovery phase. During the main phase, spread-F was generated over the stations located close to the northern crest of the EIA, and it was inhibited over Cachoeira Paulista, a station near the southern crest. During the August 2018 storm, local winter, the geomagnetic activity may have helped generate the irregularities in all the stations analysed regardless of the phase of the storm. We suggest that the generation (inhibition) of irregularities is related to the effect of eastward (westward) storm time electric fields—disturbance dynamo electric fields and prompt penetration electric fields—that created favourable (unfavourable) conditions for the generation of irregularities by uplifting (lowering) the F region.

Analysis of the Sporadic-E Layer Behavior in Different American Stations during the Days around the September 2017 Geomagnetic Storm

The development of sporadic-E (Es) layers over five Digisonde stations in the American sector is analyzed. This work aims to investigate the dynamic of such layers during the days around the geomagnetic storm that occurred on 8 September 2017. Therefore, a numerical model (MIRE) and Radio Occultation (RO) technique are used to analyze the E layer dynamics. The results show a downward movement in low-middle latitudes due to the wind components that had no significant changes before, during, and after the geomagnetic storm. In fact, our data and simulations showed weak Es layers over Boulder, Cachoeira Paulista, and Santa Maria, even though the winds were not low. However, the RO data show the terdiurnal and quarterdiurnal influence in the Es layer formation, which can explain this behavior. In addition, we observed an atypical Es layer type, slant Es layer (Ess), during the main phase of the magnetic storm over Boulder. The possible cause of the Ess layers was gravity waves. Another interesting point is the spreading Es layer occurrence associated with the Kelvin–Helmholtz Instability (KHI). Finally, it is confirmed that the disturbed electric field only influenced the Es layer dynamics in regions near the magnetic equator.

Binary Mixtures of ZnO/TiO2 for Solar Heterogeneous Photocatalysis of Non-Purgeable Organic Carbon in Landfill Leachate

Landfill leachate is a global problem that has attracted considerable attention from researchers in different areas. It is crucial to develop optimized treatment strategies for landfill leachate, given the need to minimize or eliminate negative environmental impacts resulting from the inadequate disposal of solid waste, as determined by legislation. Landfill leachate is primarily composed of humic substances, which may associate with other toxic molecules and are recalcitrant to the conventional treatments used in Brazil. This study assessed the photocatalytic degradation of carbonaceous materials in leachate collected from the Cachoeira Paulista municipal landfill, São Paulo State, Brazil. Sunlight was used as energy source without additional light inputs. Experiments were carried out in a thin-film fixed-bed reactor, using metal plates coated with paints formulated for this purpose. Paints had a low additives loading, including that of photocatalysts. We investigated the photocatalytic behavior of the binary system ZnO/TiO2 incorporated into acrylic varnish in the degradation of non-purgeable organic carbon (NPOC) in samples of humic acids and fulvic acids + humins. Reactions were conducted under acidic, neutral, or alkaline conditions. NPOC degradation was low in fulvic acid + humin samples, regardless of photocatalyst concentration or pH. The proposed process resulted in high degradation of humic acids, especially under conditions of low chemical stability, which facilitated oxidation. A maximum humic acid degradation of 65% was achieved using high concentrations of TiO2 in acidic medium.

New Findings Relating Tidal Variability and Solar Activity in the Low Latitude MLT Region

AbstractMesospheric winds have been measured by meteor radar at Cachoeira Paulista (22.7°S; 45°W) since April 1999. The tidal components were analyzed over about 21 years of available data exhibiting an annual and semi‐annual variation. Amplitudes of meridional diurnal (semidiurnal) tide are on averaged 30% (28%) and the zonal ones are 14% (20%) stronger at solar minimum than at solar maximum. The anticorrelation between F10.7 cm solar flux and amplitudes of the semiannual oscillation of diurnal and semidiurnal tides is presented. Additionally, the sporadic E (Es) layers occurrence has an anti‐correlation with solar activity due to the tidal wind variation. A discussion about the physical mechanism is performed in terms of the particle precipitation during High‐Speed Stream (HSS) events according to the solar cycle. Finally, a superposed epoch analysis of the tidal amplitudes during the HSS events in 2018 is presented. And a slight increase in all tidal components is seen when the structure reached the Earth and in the following days showing that indeed the electron precipitation during HSS events affect the tidal amplitudes.

Possible relationship of meteor disintegration in the mesosphere and enhancement of sodium atoms: A case study on july 05, 2013

• Possible relationship of meteor disintegration and enhancement of sodium atoms. • The sodium cloud was carried away by the horizontal wind and suggest that the increase in sodium density at São José dos Campos is a dynamical process. • The all-sky images show that the sodium cloud around 90 km was formed along the bright part of the fireball. Our observations show that on some occasions an influx of meteor ablation possibly contributes to appearance of a sudden enhancement in mesospheric sodium density. On July 05, 2013, all-sky images with a narrow sodium filter in the 589 nm emission, operating at Cachoeira Paulista (22.7° S, 45° W) and lidar observations of the mesospheric sodium layer, operating at São José dos Campos (23.1° S, 45.9° W), both observatories in Brazil, show a possible relationship of meteor disintegration and appearance of sodium enhancements on the background layer. After the meteor impact, the all-sky images showed a sodium cloud that was seen for about 10 min through the images in the NaD 589 nm emission, with initial dimensions of approximately 36 km × 9 km and initial speed of about 90 m/s southward. In addition, our observations show that the movement of sodium cloud in the horizontal plane around 90 km is relatively anisotropic and change the dimensions with time.

Different Sporadic‐E (Es) Layer Types Development During the August 2018 Geomagnetic Storm: Evidence of Auroral Type (Esa) Over the SAMA Region

AbstractSporadic‐E (Es) layers are investigated over five Digisonde stations located inside (Santa Maria and Cachoeira Paulista), boundary (São Luís), and outside (Millstone Hill and Port Stanley) the South American Magnetic Anomaly (SAMA) in the course of the 25 August 2018, geomagnetic storm. Data from Digisondes and ground‐based magnetometer and a numerical model of the E‐region (MIRE) are analyzed to search the roles of neutral winds and electric fields as physical processes responsible for the generation of Es layers. Moreover, it is observed for the first time over Santa Maria a type of Es layer that resembles the Esa detected in the auroral region. The characterization of such signatures in ionograms and the investigations of its formation mechanism are the main focus of this study. Hiss waves activities detected by the Van Allen Probe‐B data provide evidence that energetic particle precipitations are the most likely process responsible for this type of Es layer inside the SAMA in the night hours during the geomagnetic storm recovery phase. An attempt is also made to explain the presence of Esq over São Luís in terms of the expansion of the Equatorial Electrojet to higher latitudes. Finally, the results bring a new observational and modeling indication of a concomitant action of multiple formation mechanisms in the Es layers development in the American sector during the 25 August 2018, geomagnetic storm.

Modeling and causative mechanism of OI 630.0 nm nightglow emission over Cachoeira Paulista (22.7oS, 45oW) – Brazil: Seasonal and temporal variability

The seasonal and temporal variability of the OI 630.0 nm nightglow emissions were observed over Cachoeira Paulista (22.7 o S, 45 o W; dip latitude −35°) in Brazil by multichannel photometer during 2014 and 2015. The temporal variation of the OI 630.0 nm nightglow intensity shows a peak during post-midnight hours ( ∼ 25 h 00 LT) during the summer. During autumn, this peak is shifted towards pre-midnight at ∼ 22 h 00 LT. It is noticed that this peak again shifted towards post-midnight at 26 h30 LT and 25 h30 LT during winter and spring, respectively. The intensity increases by a factor of 2–4 in the summer than that observed in other three seasons. The modelling of the nightglow measurements in 2015 is carried out by calculating the excitation rate, emission rate and intensity of OI 630.0 nm nightglow emission in the upper atmosphere at low latitudes. Our calculation suggests that the dissociative recombination of O 2 + with electrons is the main source for the OI 630.0 nm nightglow emission. We report that the model intensities are in good agreement with the measurements at Cachoeira Paulista for all four seasons and the model reproduces all features of peak intensities very well.

Impact of the September 2019 Minor Sudden Stratospheric Warming on the Low‐Latitude Middle Atmospheric Planetary Wave Dynamics

AbstractPlanetary wave (PW) associated dynamical variability in the equatorial and extratropical middle atmosphere during the September 2019 Southern hemisphere minor sudden stratospheric warming (SSW) is investigated utilizing meteor radar wind observations from São João do Cariri (7.4°S, 36.5°W) and Cachoeira Paulista (22.7°S, 45°W) and reanalysis data. Signature of the mesospheric warming in conjunction with the stratospheric cooling is found at low latitudes. The strong westerly wind at low latitudes decelerates notably near 65 km at the onset of the warming episode, although no wind reversal is observed. The wind spectra reveal a prevalent quasi‐16‐day wave (Q16DW) prior to the SSW and existence of a quasi‐6‐day wave (Q6DW) after the warming event. Possible existence of barotropic/baroclinic instability in the low and mid latitude middle atmosphere may be responsible for exciting the Q6DW. Both traveling and stationary waves exhibit notable activities during the warming event. Although involvement of both zonal wavenumbers 1 and 2 PWs are found in the event, PW with zonal wavenumber 1 seems to play a vital role in preconditioning the same. Furthermore, significant latitudinal mixing of airmass between the tropics and high latitudes is evident in the potential vorticity map. The Eliassen‐Palm flux diagnosis shows the propagation of the Q6DW and Q16DW from mid to low latitudes during the warming event.

Ionospheric GPS-TEC responses from equatorial region to the EIA crest in the South American sector under intense space weather conditions

We present and discuss the ionospheric F-region observations from equator to the equatorial ionization anomaly (EIA) regions over the South American sector during an intense space weather event occurred between 27 and May 29, 2017. During this geomagnetic storm, the symmetric-H (SYM-H) reached a minimum of −142 nT at ∼0700 UT on May 28, 2017. For this investigation, we analyze the vertical total electron content (VTEC) observations from a chain of nearly 120 Global Positioning System (GPS) stations. Magnetometer measurements obtained at two stations in the low latitude regions are also presented. The observations do not indicate prompt penetration electric field (PPEF) effects in the VTEC variations. Magnetometer's observations over Cuiabá (CBA) and Cachoeira Paulista (CXP) in central west and south parts of Brazil, respectively, have shown a strong cross-correlation with SYM-H in the period between 3 and 48 h. The results also show positive ionospheric storm phase during the recovery phase on May 28, 2017. Positive effect during the recovery phase of the geomagnetic storm is possibly associated with effects of disturbances winds. During the recovery phase, a strong intensification of the EIA took place, possibly related to an additional ionization effect. The VTEC values show differences between the west and east sectors. This indicates that the EIA crest is stronger in the east sector than in the west sector, possibly due to the combination of disturbance wind effects and geomagnetic field geometry where in the east sector the field lines are more inclined.

Validation of COSMIC-2-Derived Ionospheric Peak Parameters Using Measurements of Ionosondes

Although numerous validations for the ionospheric peak parameters values (IPPVs) obtained from the Constellation Observing System for Meteorology, Ionosphere, and Climate (COSMIC) have been conducted using ionosonde measurements as a reference, comprehensive evaluations of the quality of the COSMIC-2 data are still undesirable, especially under geomagnetic storm conditions. In this study, the IPPVs measured by ionosondes (Ramey, Boa Vista, Sao Luis, Jicamarca, Cachoeira Paulista, and Santa Maria) during the period 1 October 2019 to 31 August 2021, are used to evaluate the quality of COSMIC-2 data over low-latitude regions of the Americas. The results show that the NmF2 (hmF2) from COSMIC-2 agrees well with the ionosonde measurements, and the correlation coefficients for the two sets of data at the above six stations are 0.93 (0.84), 0.91 (0.85), 0.91 (0.88), 0.88 (0.79), 0.96 (0.83), and 0.96 (0.87), respectively. The data quality of COSMIC-2 derived NmF2 is largely dependent on geomagnetic latitude. It was also found that NmF2 derived from COSMIC-2 tends to be underestimated over the stations in Boa Vista and Cachoeira Paulista, which are close to the crests of the equatorial ionization anomaly (EIA), whilst that of the other stations is slightly overestimated. A comparison between COSMIC-measured and ionosonde-derived hmF2 indicates that the former is systematically higher than the latter. In addition, the differences in the two NmF2 datasets derived from COSMIC-2 and ionosonde measurements at night are generally smaller than those of daytime, when the EIA is well developed, and vice versa for hmF2, whose RMSE is slightly smaller during daytime (with the exception of Ramey). Furthermore, NmF2 obtained from COSMIC-2 is shown to perform best in summer at Ramey, Boa Vista, Sao Luis, and Santa Maria, best in winter at Jicamarca and Cachoeira Paulista. Finally, the COSMIC-2 electron densities capture the ionospheric dynamic enhancements under a moderate geomagnetic storm condition very well.

Evaluation of Different Methods for Calculating the ROTI Index Over the Brazilian Sector

AbstractIonospheric irregularities as plasma bubbles occur in the ionosphere, and generally, they are characterized by the low plasma density regions. The Rate Of TEC Index (ROTI) was defined in terms of the Total Electron Content (TEC) variation and is used to characterize these plasma bubbles. It is essential to evaluate the ROTI behavior since the ionospheric irregularities can cause fluctuations in the radio signal, interfering in the ionospheric data analysis. Therefore, we performed in this work a comparative study of five different methods available to calculate the ROTI to evaluate the most suitable over the Brazilian region. The ROTI was calculated over three GNSS stations at different latitudes: São Luís (SALU, 2°31′S, 44°16′W; dip: −3.8°), Cachoeira Paulista (CHPI, 22°40'S, 44°59'W; dip: −36.4°), and Santa Maria (SMAR, 29°41′S, 53°48′W, dip: −37°). The results show that the most viable method for calculating ROTI in the Brazilian region is based on the Slant TEC equation as defined by Cherniak et al. (2018), https://doi.org/10.1007/s10291‐018‐0730‐1. Our results are supported by the comparison between the ROTI with TEC maps, ionograms collected at Fortaleza (FZA0M, 3°43'S, 38°32'W, dip: −15.8°), SALU, and CHPI and All‐Sky imagers collected at the São João do Cariri (SJCA, 7°23'S, 36°31'W, dip: −11°) and CHPI. Additionally, we observe Equatorial Plasma Bubbles (EPBs) in the Brazilian region using the ROTI index map.

Determination of sky status by ground based radiometric data analysis

Objectives: To predict meteorological phenomena such as rain events from sky status during rainy and non-rainy periods. Methods: The method used here is based on brightness temperature ratio measurement at two different frequencies, namely 23.8 GHz and 30 GHz respectively, using ground based dual frequency radiometric data. The ratios of brightness temperature readings obtained by the dual-frequency radiometer at the two above mentioned frequencies are calculated for each simultaneously-taken pair of measurements. Data obtained by the authors for the year 2009 at Cachoeira Paulista in Brazil has been used for analysis. Findings: The major results obtained from the analysis of data collected over a continuous period of seven months are used to construct corresponding histograms and cumulative count graphs of brightness temperature ratios. The histograms and graphs clearly show three peak values that could be interpreted as thresholds between clear sky, cloudy sky and rainy sky conditions respectively. Novelty: The study implements detection of rain events from sky status during rainy and non-rainy periods using peak brightness temperature values obtained from graphs generated using the observation data. The outlined technique can therefore be used to clearly determine sky conditions and accurately predict rain phenomena. The ratio of brightness temperatures at the two frequencies is a unique parameter which is critical to the successful estimation of rain from sky status. The results agree well with multi-channel radiometric data obtained by other researchers at lower frequencies. Keywords: sky status; microwave; millimeter wave; dual frequency radiometer; brightness temperature; rainfall

Monthly averages of diurnal temperature variation from meteor radar at Cachoeira Paulista (22.7°S, 45°W), Brazil

Monthly averages of the superposed values of decay times of meteor echoes from underdense meteor trails obtained by meteor radar observations at Cachoeira Paulista (22.7°S, 45°W), Brazil, have been employed to estimate temperature and to study the diurnal temperature fluctuations in the upper mesosphere and lower thermosphere region. The monthly diurnal amplitudes and phases in meteor radar temperatures at Cachoeira Paulista are comparable to those of the westward migrating diurnal tide, with zonal wave number 1, found in the reported temperatures obtained from SABER data, when the observations were obtained during the same period. The diurnal amplitudes in the temperature do not show the semiannual oscillation present in those of the diurnal tide in zonal and meridional winds. The diurnal temperature peaks 4 to 5 h ahead of diurnal tide in the zonal winds and is in anti-phase with the diurnal tide in the meridional winds. The semidiurnal amplitudes of the radar temperature fluctuations also are comparable with SABER westward migrating semidiurnal tide, with zonal wave number 2, and do not present a defined seasonal behavior, while their phases undergo small changes. They lead the semidiurnal tide in the zonal winds by about 4 h during austral summer, but it remains in-phase for the other months, and lead in meridional winds by about 5 to 8 h.

Evaluation of the Solar Quiet Reference Field (SQRF) model for space weather applications in the South America Magnetic Anomaly

In the present work, we evaluate the accuracy of the Solar Quiet Reference Field (SQRF) model for estimating and predicting the geomagnetic solar quiet (Sq) daily field variation in the South America Magnetic Anomaly (SAMA) region. This model is based on the data set of fluxgate magnetometers from 12 magnetic stations of the Embrace Magnetometer Network (Embrace MagNet) from 2010 to 2018. The model predicts the monthly average horizontal field of the geomagnetic quiet (Sq-H) daily variation solving a set of equations for the specified geographic coordinates in terms of the solar cycle activity, the day of the year, and the universal time. We carried out two comparisons between the prediction and observational data of the Sq-H field. The first part attempts to evaluate the accuracy for estimating the Sq-H field over Medianeira (MED, 25.30° S, 54.11° W, dip angle: − 33.45°) by using linear interpolation on the SQRF coefficients and comparing it with the data collected from April to December in 2018. None of the datasets collected at MED is part of the dataset used to build the SQRF model. The second part of the analysis attempts to evaluate the accuracy for predicting the quiet daily field variation over Cachoeira Paulista (CXP, 22.70° S, 45.01° W, dip angle: − 38.48°). The dataset collected at CXP before the period analyzed in the present work is part of the dataset used to build the SQRF model. Thus, the prediction accuracy is tested using magnetic data outside the time interval considered in the model. The prediction results for both locations show that this empirical model’s outputs present a good agreement with the Sq-H field obtained from the ground-based magnetometer measurements. The accuracy of the SQRF model (high correlation, r > 0.9) indicates a high potential for estimating and predicting geomagnetic quiet daily field variation. Concerning space weather applications, the model improves the scientific insight and capability of space weather prediction centers to predict the variability of the regular solar quiet field variation as reference conditions, which may include areas with no measurements.

The Impact of the Disturbed Electric Field in the Sporadic E (Es) Layer Development Over Brazilian Region

AbstractDuring disturbed periods, E region electric fields can cause anomalous Es layer behavior, which is observed in the digital ionosonde data. To investigate the influence of these electric fields in the Es layer development, we analyzed a set of 20 magnetic storms from 2015 to 2018 over Boa Vista (BV, 2.8°N, 60.7°W, dip ∼18°), São Luís (SLZ, 2.3°S, 44.2°W, dip ∼8°), and Cachoeira Paulista (CXP, 22.41°S, 45°W, dip ∼35°). The electric field zonal components during the main and recovery phases of each magnetic storm are computed to study the corresponding characteristics of these Es seen in ionograms. Additionally, a numerical model (MIRE, Portuguese acronym for E Region Ionospheric Model) is used to analyze the Es layer dynamics modification around disturbed times. Using observation data and simulations, we were able to establish a threshold value for the electric field intensity for each region that can affect the Es layer formation. The results sustain that the strong Es layer in BV can be an indicator of the disturbed dynamo event. At SLZ, on the other hand, the Es layers are affected by the competition mechanisms of their formation, as equatorial electrojet irregularities and winds, during the main phase of the magnetic storm. Over CXP, the Es layer dynamics are dominated by the wind shear mechanism. Finally, this study provides new insights into the real impact of the electric field in the Es layer development over the Brazilian sector. Thus, our results lead to a better understanding of the underlying mechanisms related to the Es layer formation and dynamics.

Observation of Postsunset OI 135.6 nm Radiance Enhancement Over South America by the GOLD Mission

AbstractThe Global‐scale Observation of Limb and Disk (GOLD) mission, for the first time, provides synoptic two‐dimensional (2D) maps of OI 135.6 nm observations. These maps describe the unambiguous and dynamic evolution of nighttime ionospheric F2‐peak electron densities (NmF2) as the 135.6 nm airglow emission radiance correlates well with NmF2 at night. On November 19, 2018, the 135.6 nm radiance measured by GOLD, NmF2 measured by a digisonde, and GPS total electron content (TEC) measurements at Cachoeira Paulista (CP) all showed a postsunset enhancement, with an increase near 22:30 universal time. The 135.6 nm radiance map showed that this enhancement was due to the southward movement of the southern equatorial ionization anomaly (EIA) crest. Therefore, the GOLD observation showed the linkage between postsunset enhancement of NmF2 and EIA movement. Furthermore, unlike the southward movement of the southern crest, the corresponding EIA northern crest, however, did not show northward motion. This is the first time that the EIA hemispheric asymmetry, which included both different densities and movement of two crests in a short time period (<2‐h), was captured. The cause of this asymmetric movement of the two crests is not clear and requires further investigation.

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

AbstractIn 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.