Fronts and thermohaline structure of the Brazil–Malvinas Confluence System

Fronts and thermohaline structure of the Brazil–Malvinas Confluence System (BMCS) are studied from climatic data, “Marathon Exp. Leg.8, 1984” data, and Sea surface temperature (SST) data base “ds277-Reynolds” (1981–2000). The South Atlantic Central Water (SACW) is divided in two main types: tropical (TW) and subtropical water (ST). Water masses, Fronts, Inter-Frontal and Frontal Zones are analysed and classified: (a) the water masses: Tropical Low-Salinity Water, Tropical Surface Water, Tropical Tropospheric Water, Subtropical Low-Salinity Water, Subtropical Surface Water, Subtropical Tropospheric Water. T,S characteristics of intermediate, deep and bottom water defined by different authors are confirmed and completed; (b) the Inter-Frontal Zones: Tropical/Brazil Current Zone, Subtropical Zone and Subantarctic Zone; (c) the Frontal Zones: Subtropical, Subantarctic and Polar, and (d) the Fronts: Subtropical Front of the Brazil Current, Principal Subtropical Front, North Subtropical Front, Subtropical Surface Front, South Subtropical Front, Subantarctic Surface Front, Subantarctic Front and Polar Front. Several stable T–S relationships are found below the friction layer and at the Fronts. The maximum gradient of the oceanographic characteristics occurs at the Brazil Current Front, which can be any of the subtropical Fronts, depending on season. Minimum mean depth of the pycnocline coincides with the Fronts of the BMCS, indicating the paths of low-salinity shelf waters into the open ocean. In the work it is shown how to recover the horizontal and vertical thermohaline structure of waters from satellite data RSMAS SST.     

Assessing the relationship between solar activity and some large scale climatic phenomena

The nature of the climatic response to solar variability is assessed over a long-time scale. The wavelet analysis applied to paleoclimatic proxy data of large scale atmospheric phenomena (North Atlantic Oscillation, Atlantic Multidecadal Oscillation, Pacific Decadal Oscillation and Southern Oscillation Index) has revealed coherence between the climatic oscillations and the solar phenomena (the cosmogenic isotope ¹⁰Be and the Total Solar Irradiance) preferentially with periods of Schwabe, Hale and Yoshimura–Gleissberg cycles that may reflect a modulation of solar activity.     

Rio de la Plata estuarine system: Relationship between river flow and frontal variability

This paper deals with the application of SeaWIFS images to characterize spatial and temporal variability of fronts in the Rio de la Plata estuarine system over the period 2000–2003. We aim to depict the relationship between river outflow and variability of fronts’ loci on monthly to ENSO-related timescales and the influence of the winds along Rio de la Plata (axial winds) on the abrupt changes in frontal dynamics over synoptic timescales. During the studied period both La Niña (July 1999–June 2000) and El Niño (April 2002–May 2003) events induced significant displacements of fronts. Three distinct fronts were analyzed between river, estuarine, coastal and marine waters of the Rio de la Plata: Main Turbidity Front, Main Marine Front, and Secondary Marine Front. Their number, location and separation seem to be mainly related to river outflow and second, to fresh (>8 m/s) axial winds. During low discharge periods (i.e. summer time and/or La Niña events) these winds induce abrupt changes in the location of fronts (100–200 km) and greater separation between them over synoptic timescale, whereas during high river discharge or ENSO years some of the variability of fronts location is explained by the river’s outflow fluctuations, especially by the high variability of the River Uruguay discharge.     

Spatial variability of the ocean color field in CZCS imagery

The mesoscale ocean color field has been investigated by means of a statistical approach to the analysis of Coastal Zone Color Scanner imagery. A quantitative assessment of ocean color was provided by deriving large scale, high resolution images of the diffuse attenuation coefficient at 490 nm, K(490), for several open ocean areas in the North Atlantic and North Pacific (around 30°, 40° and 60° N). Linear trends, power spectra and structure functions were determined for one-dimensional transects extracted from the images. These results can be interpreted as a composite statistical signature of the oceanic regions examined. In light of the relationship between ocean optical properties and concentration of dissolved and suspended materials in the water, the statistical parameters obtained provide an insight into the relative intensity and scales of patchiness of water constituents, and of the planktonic environment.     

A review of short-term climate variability mechanisms

Climate varies from seasonal to centennial time scales. In the last two decades progress has been made to better understand several aspects of short-term variability of the Earth’s climate system. Tropical Pacific is dominated by a single mode of interannual climate variability, which reflects the coupling of the Ocean and the atmosphere and is expressed by the El Niño/Southern Oscillation (ENSO) phenomenon. The Pacific climate contains another mode of variability similar to the ENSO, but varying on a decadal scale, the Pacific Decadal Oscillation (PDO) mode. Variations of the sea surface temperature (SST) in the Tropical Atlantic also play an important role in modulating the climate variability. The SST variability in this basin might be explained by at least five modes: separate modes in the Tropical North Atlantic and Tropical South Atlantic, equatorial mode, dipole mode and cross-equatorial SST anomaly gradient mode. Among these modes, the equatorial mode contains strong interannual variability, while the dipole and the cross-equatorial SST anomaly gradient modes contain strong decadal variability. Some aspects of the climate variability, with emphasis on the ENSO, PDO modes in the Pacific and the Atlantic SST modes on the interannual and decadal time scales, are discussed in the present paper.     

Solar, geomagnetic and cosmic ray intensity changes, preceding the cyclone appearances around Mexico

Recently it has been suggested that there exist specific changes in the cosmic ray intensity and some solar and geomagnetic parameters during the days, preceding the hurricane appearances over the North Atlantic Ocean. To understand better these phenomena, data for all hurricanes born not only over the Atlantic but also over the Pacific waters in the last 55 years that hit the Mexican borders were elaborated. As basic hurricane parameters the maximum rotational velocity and the estimated total energy were used. To avoid any interference all hurricanes, overlapping the preceding ones with more than 20 days were not included. Then the behavior of the cosmic ray (CR) intensity, the sunspot (SS) numbers, and the geomagnetic parameters (AP) and (KP) in 35 days prior and 20 days after the cyclone start were investigated. The CR, SS, AP and KP showed much more intensive disturbances in the periods preceding and following the hurricane appearance. For SS this disturbance gradually increase with the hurricane strength. A characteristic peak in the CR intensity appears before the hurricane start. But its place varies between 5 and 20 days before that start. Specific changes were observed in the SS. For major hurricanes they begins sometimes more than 20 days in advance. The AP and the KP show series of bursts, spread over the whole period of 30 preceding days. The obtained results from the performed correlational analysis are enough interesting to motivate a further statistical analysis with more precise techniques: in particular a common periodicity of 30 years found in the number of tropical storms landing into Mexico, the averaged rotational wind velocity and the ACE must be studied in connection with the solar Hale cycle. Using coherence wavelet spectral analysis we present a comparative study between one terrestrial and one cosmophysical phenomena that presumable influence hurricanes development: African dust outbreaks versus cosmic rays for all North Atlantic tropical cyclones. It is shown that the cosmophysical influence cannot be considered as a negligible effect.     

Ocean circulation studies in the vicinity of Southern Africa: Preliminary results using FGGE drifters and remote sensing

The three highly variable ocean circulation systems which meet south of South Africa have been studied by combining the use of satellite thermal infra-red imagery, hydrographic measurements and drifting buoys. We present a few preliminary examples where this method has been successful. These include the sources of the Agulhas Current, the influence of the Agulhas Current on the Cape upwelling region as well as the interaction of the Agulhas Current with the Subtropical Convergence. An example is also given of how a biological hypothesis concerning the recruitment of a rock lobster species at Vema Seamount has been supported by the analysis of the drifts of FGGE buoys in the South Atlantic Ocean.     

Future U.S. ocean color missions—OCI,MODIS and HIRIS

The Coastal Zone Color Scanner (CZCS) launched by the National Aeronautics and Space Administration (NASA) on the Nimbus-7 Satellite in 1978 has provided exceptionally valuable data for studies of the productivity of the ocean, fisheries, the detection of oceanic fronts and currents, and the optical properties of the ocean. NASA has been working with the scientific community, the National Oceanographic and Atmospheric Administration (NOAA), France's Centre National d'Etudes Spatiales (CNES), and industry to develop an Ocean Color Imager (OCI), a follow-on instrument which would provide the near real-time and global data necessary to fill these needs in the 1990's. The Earth Observing Satellite Company (EOSAT) is considering flying an ocean and land wide-field color instrument which would meet these needs on Landsat 6 or 7 planned for launch in 1989 and 1991, respectively. It would provide eight ocean color channels for improved atmospheric correction and in-water algorithms, global coverage and near real-time data for operational uses. In the mid 1990's NASA is planning to fly a Moderate Resolution Imaging Spectrometer (MODIS) and a High Resolution Imaging Spectrometer (HIRIS) as part of the Earth Observing System (Eos) on the Polar Platform of the Space Station. These instruments are array spectrometers which would provide full spectral resolution in the visible and infrared. This opens the possibility of separating different groups of phytoplankton, suspended sediments and other substances in the water. Also, HIRIS would have across track pointing ability which will allow high resolution rapid sampling of dynamic coastal areas and estuaries.     

Spatial and temporal scales of the Brazil–Malvinas Current confluence documented by simultaneous MODIS Aqua 1.1-km resolution SST and color images

The moderate resolution imaging spectroradiometer (MODIS) on board the Aqua satellite measures visible and infrared radiation in 36 wavebands, providing simultaneous images of sea-surface temperature (SST) and chlorophyll-a (chl-a) concentration in the upper meters of the sea. For the first time, truly synoptic SST and chl-a- concentration images are available. These images are daily and of 1.1-km resolution.The strong contrasts in sea-surface temperature and surface chlorophyll-a concentration over the southwest Atlantic make satellite infrared and color images particularly appropriate tools for studying the Brazil–Malvinas (B/M) Current confluence. We examine two years (July, 2002–June, 2004) of Aqua/MODIS infrared and color images to document the precise structure of the B/M confluence simultaneously in SST and chl-a.We first compared MODIS weekly data with simultaneous independent satellite data. Spatial and temporal distributions are similar for both SST and color. Differences between MODIS and SeaWiFS (sea-viewing wide field-of-view sensor) are large in pigment-rich regions along the coast and shelf. Here, we focused on the offshore region where differences are small.For each season, exceptionally cloud-free 1.1-km resolution MODIS images showed two thermal fronts, one corresponding to the Brazil Current’s southernmost limit, the other, to the Malvinas Current’s northernmost limit. These two fronts remained quite close to each other (within 50 km) and were separated by water with an SST and chl-a concentration typical of the continental shelf waters. In spring, the water rich in chl-a from the platform is squeezed between the two currents and entrained away from the coast in between the two thermal fronts. In the frontal region, SST gradient maxima trace the contour of the chl-a-rich water.Enlargements of the frontal region and of the turbulent region downstream of the frontal collision are presented and analyzed. MODIS documents in an unprecedented way the SST and chl-a filaments as they are distorted and mixed by meso- and sub-mesoscale structures in the strain-dominated region of the B/M confluence. It is suggested that a substantial part of the chl-a local maximum in the Malvinas return flow is of continental-shelf origin.     

Long-term variations of the surface pressure in the North Atlantic and possible association with solar activity and galactic cosmic rays

Long-term variations of the surface pressure in the North Atlantic for the period 1874–1995 (Mean Sea Level Pressure archive, Climatic Research Unit, UK) were compared with indices of solar and geomagnetic activity and the galactic cosmic ray (GCR) variations characterized by the concentration of the cosmogenic isotope ¹⁰Be. A periodicity of ∼80 yrs close to the Gleissberg cycle in the intensity of the 11-yr solar cycles was found in the pressure variations at middle latitudes (45–65°N) in the cold half of the year, which is the period of intensive cyclogenesis. It was shown that a long-term increase of pressure in this region coincided with a secular rise of solar/geomagnetic activity which was accompanied by a decrease in GCR intensity. Long-term decreases of pressure were observed during the periods of low (or decreasing) intensities of sunspot cycles. Similar features were also found in the spectral characteristics of geomagnetic activity indices, GCR intensity and pressure at middle latitudes on the quasi-decadal time scale. Effects of solar activity/GCR variations on the surface pressure seem to be more pronounced in the North Atlantic zone of intensive cyclogenesis (near the eastern coasts of North America). The results obtained suggest possible links between long-term variations in cyclonic activity at extratropical latitudes of the North Atlantic and solar activity/GCR variations on the time scales from ∼10 to ∼100 yrs.     

FY-3A观测的次南大西洋异常区形成机理

研究FY-3A卫星观测到的内辐射带质子通量分布,发现3～5MeV能道出现除南大西洋异常区以外的第二个异常区.该异常区是一个质子通量的次极值区,由于该质子通量极值区比主南大西洋异常区强度弱、面积小,因此称之为次南大西洋异常区.通过在主南大西洋异常区和次南大西洋异常区分别选取有代表性的样本点进行研究,发现内辐射带质子通量随投掷角近似呈正态分布,当投掷角在90°附近时,质子通量出现极大值;当投掷角大于120°或者小于60°时,质子通量几乎为零.此外,主南大西洋异常区质子通量在各个能道均为完全各向异性,次南大西洋异常区质子通量随着能道增高逐渐趋于各向同性.通过NOAA观测数据对此规律进行了验证,并由此解释了次南大西洋异常区的形成机理.      

Interannual variability of the zonal sea surface slope in the equatorial Atlantic during the 1990s

Altimetry data have proven themselves essential for the early detection, analysis and monitoring of large scale tropical anomalies associated with El Niño in the Pacific. Warm events in the Atlantic are much weaker than in the Pacific and are partially masked by the strong seasonal cycle. Satellite altimetric data permits one to estimate the zonal sea surface slope variations at the equator in the Atlantic with sufficient accuracy for resolving interannual sea surface slope variations. The altimetry-derived slope is here shown to detect Atlantic warm events. For all warm events, anomalies in sea surface slope tend to lead SST. In the mid-1990s’, the equatorial interannual variability is dominated by 17-month period events which exhibit the structure observed in local coupled ocean–atmosphere warm events (zonal wind stress weakening and zonal surface slope relaxation, warm SST, excess precipitation). The frequency of occurrence of these Atlantic warm events is seen to have increased during the mid-1990s.     

Semi-automatic determination of the Azores Current axis using satellite altimetry: Application to the study of the current variability during 1995–2006

Satellite altimetry has been widely used to study the variability of the ocean currents such as the Azores Current (AzC) in the North Atlantic. Most analyses are performed over the region that encloses the current, thus being somehow affected by other oceanographic signals, e.g., eddies. In this study, a new approach for extracting the axis of a zonal current solely based on satellite altimetry is presented. This is a semi-automatic procedure that searches for the maximum values of the gradient of absolute dynamic topography (ADT), using the geostrophic velocity as auxiliary information. The advantage of this approach is to allow the analyses to be performed over a buffer centered on the current axis instead of using a wider region. It is here applied to the AzC for the period June 1995–October 2006.     

Evaluating the predictability of eight Atmospheric-Oceanic signals affecting Iran’s Droughts,employing intelligence based and stochastic methods

The large-scale atmospheric-oceanic phenomena are among the main effective factors in the droughts in the Middle East, especially in Iran. Since these effects are usually delayed, their relevant signals can be useful for predicting droughts. As a result, the provision of a precise prediction of these signals can be efficient in increasing the drought prediction prospect. The current study predicts 8 cases of the most effective oceanic signals on the droughts which have been investigated in Iran. To do so, the problem-solving method with the time series prediction approach is based on the two model types intelligence-based (including multilayer perceptron [MLP] and support vector machine [SVM]) and stochastic (including Autoregressive Integrated Moving Average [ARIMA]) has been used. The model's input for each index included the time lags of the same index itself, which was determined by the autocorrelation function. Based on the evaluation criteria, the results were indicative of the weak predictability of the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO), while the Extreme Eastern Tropical Pacific sea surface temperature (Niño [1 + 2]), East Central Tropical Pacific sea surface temperature (Niño [3 + 4]), and Oceanic Niño Index (ONI) were predicted with very good accuracy, and there is a high overlap between their predictions and observations (95.9 % < R² < 99.3 %). In the extreme events also, the rate of normalized forecasting error for Niño (1 + 2), Niño (3 + 4), and ONI were in the medium (20–30 %), good (10–20 %), and excellent (0–10 %) ranges, respectively. The comparison between the models also indicates a partial superiority of the ARIMA stochastic model over the SVM and MLP models. The overall results of the study are indicative of the applicability of the predictions of the three mentioned indices as the inputs to increase precipitation and drought forecasting prospects in Iran (as well as all regions affected by them); which have the research value for further studies in terms of drought forecasting.     

Ionospheric electron density profiles at sunrise-sunset

In order to improve its representation of the dependence on time and space of the ionospheric parameters, the International Reference Ionosphere ought to take account of realistic sunrise and sunset conditions in the upper atmosphere. Such input is needed for quite a few parameters for which only day and night values were taken as input in the present IRI. Of the 24 hours of a day, true nighttime comprises a fraction of 37% at an altitude of 300 km and only 26% at 1000 km. In order to demarcate the day/night/day transition periods, the present IRI proposes solar zenith angles of 98° to 120°, depending on the altitude.Electron density profiles, obtained during these periods, have been studied with two data sources: 10 vertical-incidence sounding data observed during the meridional voyages of the research vessel “Akademik Korolev” in the Pacific Ocean; 2° data observed at the South Pole. It is shown that the height of the turning point in the sub-peak F2-layer profile and also the corresponding minimum scale height appear to be independent of latitude, season and index of geomagnetic activity. A method is discussed by which the IRI electron density profiles might be improved, in particular during these hours.     

Observations in the South Atlantic geomagnetic anomaly with intercosmos-Bulgaria-1300 during a geomagnetic storm

The region of South Atlantic Geomagnetic Anomaly (SAGA) was investigated by the Intercosmos-Bulgaria-1300 satellite, launched on August 7, 1981. On the basis of data obtained from 15 orbits during increased geomagnetic activity in August 1981, a map of the Anomaly was elaborated. Two centres of activity were identified. By means of the EMO-5 electrophotometer on board the Intercosmos-Bulgaria-1300 satellite, the atmosphere glow in lines λ 5577 Å, λ 6300 Å and λ 4278 Å was studied.     

基于SAMPEX卫星观测的南大西洋异常区高能质子动态分布特征

利用SAMPEX卫星1992年7月至2004年6月19～27MeV高能质子数据对南大西洋异常区的分布特征进行研究, 发现南大西洋异常区高能质子分布随高度及F_10.7的变化十分显著. 在540±25km高度上, 地磁较为平静时期南大西洋异常区高能质子微分通量随着F_10.7的增大而减小, 同时在F_10.7≥115sfu时减小趋势较为平缓. 对中等及以上磁暴进行统计分析发现, 磁暴期间南大西洋异常区高能质子微分通量和SYM-H指数的绝对值存在明显的反相关关系, 且地磁暴对南大西洋异常区高能质子微分通量存在明显的持续影响效应. 磁暴发生期间高能质子微分通量明显减少. 磁暴恢复相及其之后高能质子微分通量呈现较为显著的恢复过程.      

Atmospheric correction of satellite altimetry observations and sea-level variability in the NE Atlantic

Satellite altimetry provides continuous and spatially regular measurements of the height of the sea surface. Sea level responds to density changes of the water, to mass changes, due to addition or reduction of water mass, and to changes in the atmosphere above it. The present study examines the influence of atmospheric effects on sea-level variability in the North-East Atlantic. The association between the height of the sea surface and the North Atlantic Oscillation (NAO) is investigated by considering different sets of altimetry measurements for which the atmospheric effects have been handled differently. Altimetry data not corrected for atmospheric effects are strongly anti-correlated with the state of the NAO, reflecting the hydrostatic response of sea-level to the NAO pressure dipole. The application of an atmospheric correction to satellite altimetry observations in the NE Atlantic decreases variability of the height time series by more than 70% and reduces the amplitude of the seasonal cycle by ∼5 cm. Altimetry data for which atmospheric effects are removed via an inverse barometer correction show a non-negligible correlation with the NAO index at some locations suggesting further indirect non-hydrostatic influences of the state of the NAO on sea level variability.     

Investigation into impact of tropical cyclones on the ionosphere using GPS sounding and NCEP/NCAR Reanalysis data

Ionospheric response to tropical cyclones (TCs) was estimated experimentally on the example of three powerful cyclones – KATRINA (23–31 August 2005), RITA (18–26 September 2005), and WILMA (15–25 October 2005). These TCs were active near the USA Atlantic coast. Investigation was based on Total Electron Content (TEC) data from the international network of two-frequency ground-based GPS receivers and the NCEP/NCAR Reanalysis data. We studied the spatial–temporal dynamics of wave TEC disturbances over two periods of ranges (02–20 min and 20–60 min). To select the ionospheric disturbances which were most likely to be associated with the cyclones, maps of TEC disturbances were compared with those of meteorological parameters.     

Space radiation quality factor investigations with “NAUSICAA”-device on board the “MIR” space station

The estimation of radiation quality factor in space flights is a serious problem of space dosimetry. The solution of this problem is based on LET-spectra measurements. The “NAUSICAA”-device installed on the “MIR” station has a detector with a large geometric factor, that gives the possibility of measuring LET-spectra with sufficient statistic in relatively short time interval and hence the corresponding Q. LET-spectra are accumulated through 24 hour periods and equivalent dose (H), absorbed dose (D), quality factor and flux (F) are measured every 10 minutes. The obtained data permit the estimate of the diurnal Q and Q in South Atlantic Anomaly. These values vary in the range of 1.4 – 2.2. The analysis of these values including their comparison with the calculated results is given in this paper.