ALBERT

Description: In this study we investigate the response of the equatorial F layer to disturbance zonal electric field associated with IMF (interplanetary magnetic field) variations dominated by a strong northward Bz episode during the magnetic storm that occurred on 21 January, 2005. We compared the results obtained from Digisondes operated at Fortaleza, Brazil (Geogr. 3.9°S, 38.45°W; dip angle: −11.7°) and Jicamarca, Peru (Geogr. 12.0°S, 76.8°W; dip angle: 0.64°). A large auroral activity (AE) intensification that occurred at ∼1715 UT produced a large F-layer peak height increase (from 300 km to 600 km) over Jicamarca with no noticeable simultaneous effect over Fortaleza. Then the Bz turning northward at ∼1940 UT with a rapid change in AE that was accompanied by a large decrease of F layer height and total suppression of the PRE over Fortaleza with no simultaneous effect over Jicamarca. Strong increase in the AE index (from ∼400 to 1000 nT) with superimposed oscillations, under Bz North, that soon followed was associated with increases in both the F layer height and the vertical drift velocity over Fortaleza (at 2130 UT), with no corresponding signatures over Jicamarca. These remarkable contrasting responses to prompt penetration electric field (PPEF) as well as to disturbance wind dynamo electric field (DDEF) and other effects observed at the two locations separated only by 2 h in LT in the South American sector are presented and discussed in this paper. Effects on spread-F development and foF2 behavior during this storm event are also addressed in this work.

Description: SST trends measured in the Somalia region during the southwest monsoon season over the period 1982-2013 have shown the existence of a warming-cooling dipole. The positive spot, with a warming trend on the order of 0.37ºC dec -1 , is centered around 5.1 ºN – 50.3º E and the negative one, with a trend on the order of -0.43ºC dec -1 , around 11.1 ºN – 52.2º E. The migration of the Great Whirl (GW) over the last three decades at a speed of -0.3 deg dec -1 in longitude and -0.6 deg dec -1 in latitude was considered as the possible origin of the SST dipole. The displacement of the GW produces changes in the geostrophic currents which, in turn, generate changes in the amount of advected water from and to coast. This article is protected by copyright. All rights reserved.

Description: La Guajira upwelling system has shown a moderate cooling (∼ -0.05 ºC dec −1 ) over the period 1982 - 2014 for the months with strong upwelling (JFM). This contrasts with the general warming observed for most of the Caribbean region (∼0.25 ºC dec −1 ) over the same period. Cooling is in good agreement with the upwelling increase (∼0.04 m 2 s −1 dec −1 ) observed in the region during winter months, although the position of the peaks in upwelling and SST trends does not coincide exactly due to the presence of the Caribbean Coastal Undercurrent. This article is protected by copyright. All rights reserved.

Description: The dynamics of equatorial ionospheric plasma bubbles over Brazilian sector during two magnetic storm events are investigated in this work. The observations were made at varying phases of magnetic disturbances when the bubble zonal drift velocity was found to reverse westward from its normally eastward velocity. Calculation of the zonal drift based on a realistic low latitude ionosphere modeled by the Sheffield University Plasmasphere-Ionosphere Model (SUPIM) showed on a quantitative basis a clear competition between vertical Hall electric field and disturbance zonal winds on the variations observed in the zonal velocity of the plasma bubble. The Hall electric field arising from enhanced ratio of field line integrated conductivities, Σ H /Σ P , is most often generated by an increase in the integrated Hall conductivity, arising from enhanced energetic particle precipitation in the South American Magnetic Anomaly (SAMA) region for which evidence is provided from observation of anomalous sporadic E layers over Cachoeira Paulista and Fortaleza. Such sporadic E layers are also by themselves evidence for the development of the Hall electric field that modifies the zonal drift.

Description: In the present work, we investigate the behavior of the equatorial F region zonal plasma drifts over the Peruvian region under magnetically disturbed conditions during two solar minimum epochs, one of them being the recent prolonged solar activity minimum. The study utilizes the vertical and zonal components of the plasma drifts measured by the Jicamarca (11.95° S; 76.87° W) incoherent scatter radar during two events that occurred on 10 April 1997 and 24 June 2008 and model calculation of the zonal drift in a realistic ionosphere simulated by the SUPIM-INPE. Two main points are focused: (1) the connection between electric fields and plasma drifts under prompt penetration electric field during a disturbed periods and (2) anomalous behavior of daytime zonal drift in the absence of any magnetic storm. A perfect anticorrelation between vertical and zonal drifts was observed during the night and in the initial and growth phases of the magnetic storm. For the first time, based on a realistic low latitude ionosphere, we will show, on a detailed quantitative basis, that this anticorrelation is driven mainly by a vertical Hall electric field induced by the primary zonal electric field in the presence of an enhanced nighttime E region ionization. It is shown that an increase in the field line integrated Hall-to-Pedersen conductivity ratio , that can arise from precipitation of energetic particles in the region of the South American Magnetic Anomaly (SAMA), is capable of explaining the observed anti correlation between the vertical and zonal plasma drifts. Evidence for the particle ionization is provided from the occurrence of anomalous sporadic E layers over the low latitude station, Cachoeira Paulista (22.67° S; 44.9° W) – Brazil. It will also be shown that the zonal plasma drift reversal to eastward in the afternoon two hours earlier than its reference quiet time pattern is possibly caused by weakening of the zonal wind system during the prolonged solar minimum period.

Description: [1]  A study of the dependence of the equatorial evening F region vertical drift velocity on solar EUV flux and F10.7 index is presented here, based on the vertical drift data obtained from Digisondes operated in São Luis (44.2º W, 2.33º S, dip angle: -2.7º) and Fortaleza (38.45º W, 3.9º S, dip angle: -11.5º) in Brazil. Previous studies on the vertical drift dependence on solar flux have addressed only the dependence on F10.7 index. The data analyzed here are from the months of October, November and December of the years from 2001 to 2009, and the analysis was done for magnetically quiet and disturbed conditions. The results show that while the drift velocity peak is strongly dependent on both solar emission fluxes, the degrees of such dependence is higher for the EUV flux than for the F10.7 index in a consistent way as judged from its identical behavior at both São Luis and Fortaleza. The study also reveals different degrees of the vertical drift dependence on solar flux for magnetic quiet and disturbed conditions, the nature of which is investigated using an example of a storm time case study.

Description: For over three decades, opposed-jets reactors have been applied particularly for fast complex chemical reactions where mixing affects the final product distribution. The first opposed-jets reactors, i.e., confined impinging jets (CIJ), had cylindrical geometries. With the advent of microreactors, a new type of prismatic opposed-jets reactors has been introduced, the so-called T-jets reactors. The state of the art of the know-how on mixing in CIJ reactors as well as the current state of the art of T-jets reactors is described. T-jets and CIJ are generally small-scale devices, ensuring that these units can mix fluids within very short mixing times on the order of milliseconds. The small scale has the disadvantage of compromising the reactors' throughput. This fact can prevent the dissemination of this type of mixers to applications where conventional reactors, such as stirred tanks, are used. Attention is paid to the issue on how to scale up opposed-jets reactors without compromising mixing times. A short analysis of the main research questions to be answered in this field is made. With the introduction of microreactors, a new type of prismatic opposed-jets reactors, the so-called T-jets reactors, have found wide-spread application. The state of the art concerning mixing in confined impinging jets reactors and T-jets reactors is described. Attempts to scale up opposed-jets reactors without compromising mixing times are analyzed.

Description: A South Atlantic ring is studied through remote sensing altimetry, hydrographic stations and drifters' trajectories. The ring's core was characterized by warmer and saltier Indian Ocean waters. At the time of the cruise the ring's signature extended out 110 km and down to 2000 m, and its core absolute dynamic topography (ADT) exceeded the surrounding Atlantic Ocean waters in 0.4 m. The geostrophic velocities were anticyclonic with maximum velocities about 35 cm s −1 at 100 m and reaching negligible values near 4500 m. The rotational transport inside the ring was 33 Sv in the thermocline and intermediate layers. The drifters' data distinguishes a 30-km core revolving as a solid body with periodicity near 5 days and a transitional band that revolves with constant tangential velocity, resembling a Rankine vortex. The ADT data identifies the ring's track, showing that it was shed by the Agulhas Current retroflection in November 2009 and propagated northwest rapidly during the first two months (mean speed ca. 10 cm s −1 ) but slowed down substantially (3-4 cm s −1 ) between March and July 2010, when it was last detected. The altimetry data also outlines the evolution of the ring's core ADT, radius, vorticity and, through a simple calibration with the cruise data, rotational transport. In particular, the ring surface and mean vorticity decay with time scales of 373 and 230 days, respectively, indicating that most of the property anomalies contained by the ring are diffused out to the subtropical gyre before it reaches the western boundary current system.