Investigação dos processos hidrossedimentológicos em parcela experimental no semi-árido potiguar

In northeastern semiarid, seasonality on precipitation temporal distribution, high intensity storm events and inadequate management of native vegetation can promote soil erosion. Vegetation removal causes soil surface exposure, reduces soil water storage capacity and can be the source degradation processes. In this context, this approach aims to analyze water and soil erosion processes on a 250 m2 undisturbed experimental plot with native vegetation, slope 2.5% by using 2006 and 2007 monitoring data. The site was instrumented to monitor rainfall, overland flow runoff and erosion by using a 5 m³ tank downstream the plot. Soil erosion monitoring was made by transported sediment and organic matter collection after each event. Field infiltration experiments were made at 16 points randomly distributed within the plot area by using a constant head infiltrometer during drought and rainy seasons, respectively. Infiltration data revealed high spatial and temporal variability. It was observed that during the beginning of the rainy period, 77% of the events showed runoff coefficient less than 0.05. As the rainy season began, soil water increase produced annual species germination. High intensity storms resulted in runoff coefficients varying between 0.33 and 0.42. Once the annual species was established, it was observed that approximately 39% of the events produced no runoff, which reflects an increase on soil water retention capacity caused by the vegetation. A gradual runoff reduction during the rainy season emphasizes the effect of vegetative density increase. Soil erosion observed data allowed to fit an empirical relationship involving soil loss and precipitation height, which was used to analyze the plot installation impact on soil erosion. Observed soil loss in 2006 and 2007 was 230 Kg/ha and 54 Kg/ha, respectively

Avaliação da produção de sedimento na bacia hidrográfica do rio Potengi através do modelo SWAT

Anthropic disturbances in watersheds, such as inappropriate building development, disorderly land occupation and unplanned land use, may strengthen the sediment yield and the inflow into the estuary, leading to siltation, changes in the reach channel conformation, and ecosystem/water quality problems. Faced with such context, this study aims to assess the applicability of SWAT model to estimate, even in a preliminary way, the sediment yield distribution along the Potengi River watershed, as well as its contribution to the estuary. Furthermore, an assessment of its erosion susceptibility was used for comparison. The susceptibility map was developed by overlaying rainfall erosivity, soil erodibility, the slope of the terrain and land cover. In order to overlap these maps, a multi-criteria analysis through AHP method was applied. The SWAT was run using a five year period (1997-2001), considering three different scenarios based on different sorts of human interference: a) agriculture; b) pasture; and c) no interference (background). Results were analyzed in terms of surface runoff, sediment yield and their propagation along each river section, so that it was possible to find that the regions in the extreme west of the watershed and in the downstream portions returned higher values of sediment yield, reaching respectively 2.8 e 5.1 ton/ha.year, whereas central areas, which were less susceptible, returned the lowest values, never more than 0.7 ton/ha.ano. It was also noticed that in the west sub-watersheds, where one can observe the headwaters, sediment yield was naturally forced by high declivity and weak soils. In another hand, results suggest that the eastern part would not contribute to the sediment inflow into the estuary in a significant way, and the larger part of the sediment yield in that place is due to anthropic activities. For the central region, the analysis of sediment propagation indicates deposition predominance in opposition to transport. Thus, it s not expected that isolated rain storms occurring in the upstream river portions would significantly provide the estuary with sediment. Because the model calibration process hasn t been done yet, it becomes essential to emphasize that values presented here as results should not be applied for pratical aims. Even so, this work warns about the risks of a growth in the alteration of natural land cover, mainly in areas closer to the headwaters and in the downstream Potengi River

Efeitos de tempestades magnéticas em sinais de gps, em Natal, Brasil

Satellites signals present disturbances (scintillations), due to presence of irregularities in the ionospheric plasma. In the present work, we dedicate to the study of the attenuation of these scintillations that is, an improvement in the signal, during the main magnetic storm phase during the period of October 2006 to February 2007. Using amplitude of scintillation 1.5GHz (L1) data of the net of satellites GPS, in the ionospheric station of Natal (5.84o S, 35.20o O, -20o dip) and geomagnetic indices, during the minimum solar cycle (referred to as cycle 23), demonstrating its anti-correlation between magnetic activity (Kp) and index of scintillation () (Bonelli2005 method, that works for solar maximum, Bonelli(2005)). These results show that these storms correspond to category I of Aarons (1991). The magnetic storms can generate irregularities when the electric feld of penetration eastward on the pre-reversal hour intensificating that and can too generate irregularities on midnight and sunlight period. The limitation of the method applied here is that it is not considering some storms that had also occurred during equinox and summer in the Brazilian region. For this reason, we will use additional data of the stations of São João de Cariri (Imager and Photometer) and of the station at Fortaleza (Digissonde data), as aid to analyze these storms. The storms that had been left out by the applied method, fit in the other two categories of Aarons, with one only exception (storm of January, 02). We show that in the day of the main phase of the magnetic storm, and with presence of bubbles (according to data of the Imager and Photometer), the speed of vertical drift ~E ~B (hF=t) is below 20m/s, that is the threshold found for Anderson al., (2004) (>20m/s as condition favorable to the formation of irregularities and increase in the scintillation index). This reduction of the speed is due to solar minimum

Estudos de distúrbios ionosféricos propagantes de larga escala (LSTID’S) na região equatorial durante grandes tempestades magnéticas: estudo de casos

The Ionospheric Disturbances – TIDs – are irregularities on the ionospheric plasma propagating in speeds in the order of tens to a few hundreds of meters per second. This present study detected and characterized the TIDs of LSTIDs (Large Scale Travelling Ionospheric Disturbance) type at low latitudes during intense geomagnetic storms and its propagation over the Brazilian sector. This work also shows as being the first to report systematically propagation of gravity waves over Natal. For this purpose, we used ionospheric records obtained from type of digisonde CADI (Canadiam Advanced Digital Ionosonde) located in Natal and the type DSP (Digisonde Portable Souder) located in Cachoeira Paulista, Fortaleza and São Luis, whereupon we used a dataset of 12 years collected by INPE (National Institute of Space Research). In this study, both calm days, that preceded the storms, and the geomagnetically disturbed days were related during the years 2000 and 1012, which cover a period of maximum and minimum solar activity. And it is presented the variations that happened in the electron density from region F of the ionosphere over the Brazilian sector, especially near the Equator (Natal, Fortaleza and São Luis), caused by ionospheric disturbances in the equatorial region during intense geomagnetic storms, because, as we know of the literature in this area, this phenomenon contributes positively to the emergence of LSTIDs in the auroral region, which may move to the equatorial region where a few cases have been documented and studied systematically. From the observation of signatures if TIDs in ionogram records, a study of the morphology of these events was performed and compared with the main characteristics of the wave of this phenomenon during great magnetic storms, i.e., DST <(-200 nT) and KP > 6. Thus, we obtained the main characteristics of TIDs over our region, i.e., period, vertical wavelength, phase and propagation speed, as well as the delay of these disturbances compared to the beginning of the magnetic storms to the Brazilian Sector.

Estudo sobre a relação entre a atividade geomagnética e cintilações de sinais de GPS em Natal-RN (Brasil)

To identify the relationship between GPS scintillation in Natal-RN (Brazil) and geomagnetic disturbances of any intensities and variations, this work made analysis of the ionospheric behavior and magnetic indexes (Dst , AE and Bz of the interplanetary magnetic field) concerning to different periods of the solar cycle between 2000 and 2014. Part of the data of this research originated at the UFRN observatory, from a GEC Plessey board connected to an ANP -C 114 antenna, modified by Cornell University’s Space group Plasma Physics in order to operate the ScintMon, a GPS monitoring program. This study, therefore, found several cases of inhibited scintillations after the main phase of magnetic storms, a fact that, along with others, corroborated with categorization of Aarons (1991) and models of disturbed dynamo (according to Bonelli, 2008) and over-shielding penetration, defended by Kelley et al. (1979) and Abdu (2011) [4]. In addition to these findings, different morphologies were noted in such disruptions in the GPS signal in accordance with previous magnetic activities. It also found a moderate relationship (R2 = 0.52) between the Dst rate (concerning to specific time) and the average of S4 through a polynomial function. This finding therefore, corroborating Ilma et al. (2012) [17], is an important evidence that the scintillation GPS are not directly controlled by magnetic induction of storms. Completing this work, this relation did show itself as a way of partial predicting of scintillations.

Estudo da variabilidade da deriva vertical do plasma ionosférico sobre a região de Natal/RN, Fortaleza/CE e Cachoeira Paulista/SP para alguns casos de tempestades magnéticas de abril a setembro de 2000

In this work are presented the results of research on the variation of vertical plasma drift from the F layer that commonly occurs during the period close to the going down of the sun (between 21UT - 22UT), and consisting of an increase in the F layer in time of day and a drop at night on the cities of Natal / RN (The 33.7º, 5.6º S), Fortaleza / CE (38.45º O, 3.9º S) and Cachoeira Paulista / SP (45.0ºO, 22.7º S ). Thus, data was used (ionograms) virtual height t ( h' ) as a function of the frequency F for the layer of the ionosphere. These data were collected through ionossonda type CADI (Canadian Advanced Digital Ionosonde) to the cities of Natal and Fortaleza, and the Digisonde DPS to the town of Cachoeira Paulista. They considered only the data available 2000 maximum solar year. With the virtual height ( h' ) data reduced in the frequencies of 6MHz and 5MHz, the next step was to calculate. The results showed that the variability of the vertical drift rate F ionospheric layer periods of magnetic storms is related both to the penetration of the electric fields as the disturbance dynamo electric fields.

Análise estratigráfica da sequência mesodevoniana-eocarbonífera da Bacia do Parnaíba, nordeste do Brasil

The Middle Devonian-Early Carboniferous sequence of the Parnaíba Basin, lithostratigraphically defined as Canindé Group, has been reinterpreted using the basic model of sequence stratigraphy. Therefore, lithology and gamma ray well-logs and seismic lines of central portion of the basin were analyzed, producing up from there diagrams 1D, isochore maps and stratigraphic sections. As results of this study, were defined two depositional cycles of second order, referred as Depositional Sequence 1 (SEQ1) and the Depositional Sequence 2 (SEQ2). The SEQ1, with interval about 37 Ma, is limited below by Early Devonian Unconformity and is equivalent to the formations Itaim, Pimenteiras and Cabeças. The SEQ2, which follows, comprises a range of about 15 Ma and is equivalent to the Longá Formation The SEQ1 starts with the lowstand systems tract, consisting of progradational parasequence set in the basal part, predominantly pelitic, deposited on a prodelta under influence of storms and the upper part consists in sandstones of deltaic front, with the maximum regressive surface on the upper limit. The transgressive systems tract, deposited above, is characterized by retrogradacional parasequence set composed of shallow shelf mudstones, deposited under storm conditions. The maximum flooding surface, upper limit of this tract, is positioned in a shale level whose radioactivity in gammaray well-log is close to 150 API. The highstand systems tract presents progradational parasequence set, comprising mudstones and sandstones deposited in shelf, fluvial-estuarine or deltaic and periglacial environments, with the upper limit the Late Devonian Unconformity. The SEQ2 was deposited in shelf environment, starting with the lowstand systems tract, that is characterized by a progradational parasequence set, followed by the transgressive systems tract, with retrogradational character. The upper limit of the tract corresponding to the fusion between maximum flooding surface with the upper limit of this sequence, which is the Early Carboniferous Unconformity, where the overlapping section was eroded. This section, which corresponds the highstand systems tract is restricted to portions at which the erosion that generate the Early-Carboniferous Unconformity was less effective, preserving the records of this unit.

Análise estratigráfica da sequência mesodevoniana-eocarbonífera da Bacia do Parnaíba, nordeste do Brasil

The Middle Devonian-Early Carboniferous sequence of the Parnaíba Basin, lithostratigraphically defined as Canindé Group, has been reinterpreted using the basic model of sequence stratigraphy. Therefore, lithology and gamma ray well-logs and seismic lines of central portion of the basin were analyzed, producing up from there diagrams 1D, isochore maps and stratigraphic sections. As results of this study, were defined two depositional cycles of second order, referred as Depositional Sequence 1 (SEQ1) and the Depositional Sequence 2 (SEQ2). The SEQ1, with interval about 37 Ma, is limited below by Early Devonian Unconformity and is equivalent to the formations Itaim, Pimenteiras and Cabeças. The SEQ2, which follows, comprises a range of about 15 Ma and is equivalent to the Longá Formation The SEQ1 starts with the lowstand systems tract, consisting of progradational parasequence set in the basal part, predominantly pelitic, deposited on a prodelta under influence of storms and the upper part consists in sandstones of deltaic front, with the maximum regressive surface on the upper limit. The transgressive systems tract, deposited above, is characterized by retrogradacional parasequence set composed of shallow shelf mudstones, deposited under storm conditions. The maximum flooding surface, upper limit of this tract, is positioned in a shale level whose radioactivity in gammaray well-log is close to 150 API. The highstand systems tract presents progradational parasequence set, comprising mudstones and sandstones deposited in shelf, fluvial-estuarine or deltaic and periglacial environments, with the upper limit the Late Devonian Unconformity. The SEQ2 was deposited in shelf environment, starting with the lowstand systems tract, that is characterized by a progradational parasequence set, followed by the transgressive systems tract, with retrogradational character. The upper limit of the tract corresponding to the fusion between maximum flooding surface with the upper limit of this sequence, which is the Early Carboniferous Unconformity, where the overlapping section was eroded. This section, which corresponds the highstand systems tract is restricted to portions at which the erosion that generate the Early-Carboniferous Unconformity was less effective, preserving the records of this unit.