O presente trabalho teve como finalidade estudar os efeitos das variações do vento resultantes de ocorrências do fenômeno El Niño-Southern Oscillation (ENSO) nos padrões da circulação superficial ao longo da costa peruana, através da análise de dados observados e de modelagem numérica. É enfocado o período 1991-2000, quando ocorreram fortes eventos La Niña (1996-97, 1998-2000) e El Niño (1997- 98). Esses eventos tiveram fortes impactos em escala global mas muito pouco se sabe sobre os impactos locais na estrutura da termoclina e no ciclo da dinâmica de Ekman ao longo da costa peruana. Os dados analisados no presente estudo foram dados coletados em duas radiais ao longo das latitudes 5 S e 15 S. O modelo oceânico utilizado foi o Modelo da Universidade de Princeton (Princeton Ocean Model-POM). As simulações numéricas foram forçadas com produtos de vento relativos ao período 1991-2000. Essas simulações reproduziram satisfatoriamente os padrões médios da circulação na região de estudo, confirmando que nas áreas próximas da costa o vento é o principal mecanismo gerador de ressurgência ou subsidência. Os resultados mostraram que durante a ocorrência do forte evento El Niño 1997-1998, nas radiais de 5 S e 15 S, houve uma drástica alteração do sistema de ressurgência costeira em resposta às variações do vento. / The objective of the present work was to study the effects of variability in the wind due to the El Niño-Southern Oscillation events in the surface circulation patterns of the Peruvian coast, by means of data analysis and numerical modeling. It is focused the period 1991-2000, when it was observed strong La Niña (1996-1997, 1998-2000) and El Niño events (1997-98). These events had strong effects worlwide but very little is known on the local impacts on the circulation, thermocline structure and the Ekman dynamics of the Peruvian coast. The data analysed in the present study were collected on transects along 5 S and 15 S. The model used was an implementation of the Princeton Ocean Model (POM). The numerical simulations were forced with wind products relative to the period of interest (1991-2000). The simulations reproduced satisfactorily the mean circulation patterns in the study area, confirming that the in the nearshore region the wind is the main driving mechanism for coastal upwelling/downwelling. The results show that during the strong 1997-1998 El Niño, a drastic alteration of the coastal upwelling system ocurred in response to the changes in the wind.

O presente trabalho teve como finalidade estudar os efeitos das variações do vento resultantes de ocorrências do fenômeno El Niño-Southern Oscillation (ENSO) nos padrões da circulação superficial ao longo da costa peruana, através da análise de dados observados e de modelagem numérica. É enfocado o período 1991-2000, quando ocorreram fortes eventos La Niña (1996-97, 1998-2000) e El Niño (1997- 98). Esses eventos tiveram fortes impactos em escala global mas muito pouco se sabe sobre os impactos locais na estrutura da termoclina e no ciclo da dinâmica de Ekman ao longo da costa peruana. Os dados analisados no presente estudo foram dados coletados em duas radiais ao longo das latitudes 5 S e 15 S. O modelo oceânico utilizado foi o Modelo da Universidade de Princeton (Princeton Ocean Model-POM). As simulações numéricas foram forçadas com produtos de vento relativos ao período 1991-2000. Essas simulações reproduziram satisfatoriamente os padrões médios da circulação na região de estudo, confirmando que nas áreas próximas da costa o vento é o principal mecanismo gerador de ressurgência ou subsidência. Os resultados mostraram que durante a ocorrência do forte evento El Niño 1997-1998, nas radiais de 5 S e 15 S, houve uma drástica alteração do sistema de ressurgência costeira em resposta às variações do vento. / The objective of the present work was to study the effects of variability in the wind due to the El Niño-Southern Oscillation events in the surface circulation patterns of the Peruvian coast, by means of data analysis and numerical modeling. It is focused the period 1991-2000, when it was observed strong La Niña (1996-1997, 1998-2000) and El Niño events (1997-98). These events had strong effects worlwide but very little is known on the local impacts on the circulation, thermocline structure and the Ekman dynamics of the Peruvian coast. The data analysed in the present study were collected on transects along 5 S and 15 S. The model used was an implementation of the Princeton Ocean Model (POM). The numerical simulations were forced with wind products relative to the period of interest (1991-2000). The simulations reproduced satisfactorily the mean circulation patterns in the study area, confirming that the in the nearshore region the wind is the main driving mechanism for coastal upwelling/downwelling. The results show that during the strong 1997-1998 El Niño, a drastic alteration of the coastal upwelling system ocurred in response to the changes in the wind.

In this thesis, the relationship between several high-latitude phenomena and the ionospheric conductance in both hemispheres is studied theoretically and experimentally. </p>Theoretically, the high-latitude electrodynamics is studied by considering currents in the magnetosphere-ionosphere system resulting from the ionospheric sheet current redistribution between the conjugate ionospheres. It is shown that strong flow between the conjugate ionospheres, the interhemispheric currents (IHC), can be set up if the conductance distribution is asymmetric in the conjugate ionospheric regions. Such conditions are typical for solstices owing to the differences in the solar illumination. Analytical and numerical modeling shows that IHCs can appear in the regions of strong conductance gradient, more specifically around the solar terminator line, and that the intensity of the IHCs can be comparable to the intensity of the well known Region 1/Region 2 currents. The effect of IHC excitation on observable magnetic perturbations on the ground is investigated. It is shown that in the vicinity of the solar terminator line, the pattern of magnetic perturbation can be such that an apparent equivalent current vortex can be detected. In addition, strong conductance gradients are shown to affect significantly the quality of the ionospheric plasma flow estimates from the ground-based magnetometer data. </p>Experimentally, the effect of the nightside ionospheric conductance on occurrence of substorms, global storm sudden commencement and radar auroras is investigated. To characterize substorm occurrence, new parameters, the derivatives of the classical AE and AO indices, are introduced. It is shown that the seasonal and diurnal variations of these parameters are controlled by the total nightside ionospheric conductance in the conjugate regions. The substorm onsets preferentially occur at low levels of the total conductance, which is consistent with the idea of the substorm triggering through the magnetosphere-ionosphere feedback instability. It is hypothesized that the total conductance affects the global storm onsets as well. To check this idea, the 33-year sudden storm commencement (SSC) data are considered. The semiannual, annual, semidiurnal, and diurnal variations in the SSC occurrence rate are found to be significant and these components exhibit a strong relationship with the total conductance of the high-latitude ionospheres. Finally, the SuperDARN midnight echo occurrence is shown to correlate, for some radars, with the total conductance minima and presumably with electric field maxima, which is consistent with general expectation that the F-region irregularities occur preferentially during times of enhanced electric fields. The gradients of the high-latitude conductance can also lead to significant errors in the plasma convection estimates from the ground-based magnetometers, and to investigate this effect a statistical assessment of the difference between the true plasma convection (SuperDARN) and the magnetometer-inferred equivalent convection direction is performed. The largest differences are found for the transition region between the dark and sunlit ionospheres and in the midnight sector where strong conductance gradients are expected due to particle precipitation. Consideration of regular conductance gradients due to solar illumination improves the agreement between the radar and magnetometer data. Finally, an attempt is made to demonstrate the effects of conductance upon the properties of traveling convection vortices (TCVs). Joint SuperDARN and magnetometer data reveal that there is resemblance between the magnetometer and radar inferred TCV images on a scale of thousands of kilometers. However, on a smaller scale of hundreds of kilometers, significant differences are observed.

In this thesis, the relationship between several high-latitude phenomena and the ionospheric conductance in both hemispheres is studied theoretically and experimentally. </p>Theoretically, the high-latitude electrodynamics is studied by considering currents in the magnetosphere-ionosphere system resulting from the ionospheric sheet current redistribution between the conjugate ionospheres. It is shown that strong flow between the conjugate ionospheres, the interhemispheric currents (IHC), can be set up if the conductance distribution is asymmetric in the conjugate ionospheric regions. Such conditions are typical for solstices owing to the differences in the solar illumination. Analytical and numerical modeling shows that IHCs can appear in the regions of strong conductance gradient, more specifically around the solar terminator line, and that the intensity of the IHCs can be comparable to the intensity of the well known Region 1/Region 2 currents. The effect of IHC excitation on observable magnetic perturbations on the ground is investigated. It is shown that in the vicinity of the solar terminator line, the pattern of magnetic perturbation can be such that an apparent equivalent current vortex can be detected. In addition, strong conductance gradients are shown to affect significantly the quality of the ionospheric plasma flow estimates from the ground-based magnetometer data. </p>Experimentally, the effect of the nightside ionospheric conductance on occurrence of substorms, global storm sudden commencement and radar auroras is investigated. To characterize substorm occurrence, new parameters, the derivatives of the classical AE and AO indices, are introduced. It is shown that the seasonal and diurnal variations of these parameters are controlled by the total nightside ionospheric conductance in the conjugate regions. The substorm onsets preferentially occur at low levels of the total conductance, which is consistent with the idea of the substorm triggering through the magnetosphere-ionosphere feedback instability. It is hypothesized that the total conductance affects the global storm onsets as well. To check this idea, the 33-year sudden storm commencement (SSC) data are considered. The semiannual, annual, semidiurnal, and diurnal variations in the SSC occurrence rate are found to be significant and these components exhibit a strong relationship with the total conductance of the high-latitude ionospheres. Finally, the SuperDARN midnight echo occurrence is shown to correlate, for some radars, with the total conductance minima and presumably with electric field maxima, which is consistent with general expectation that the F-region irregularities occur preferentially during times of enhanced electric fields. The gradients of the high-latitude conductance can also lead to significant errors in the plasma convection estimates from the ground-based magnetometers, and to investigate this effect a statistical assessment of the difference between the true plasma convection (SuperDARN) and the magnetometer-inferred equivalent convection direction is performed. The largest differences are found for the transition region between the dark and sunlit ionospheres and in the midnight sector where strong conductance gradients are expected due to particle precipitation. Consideration of regular conductance gradients due to solar illumination improves the agreement between the radar and magnetometer data. Finally, an attempt is made to demonstrate the effects of conductance upon the properties of traveling convection vortices (TCVs). Joint SuperDARN and magnetometer data reveal that there is resemblance between the magnetometer and radar inferred TCV images on a scale of thousands of kilometers. However, on a smaller scale of hundreds of kilometers, significant differences are observed.

The presence of turnip crinkle virus (TCV) in Arabidopsis thaliana plants has previously been shown to suppress the ability of these plants to produce a hypersensitive response (HR) upon inoculation with pathogens that would normally elicit this defense response. The ecotype Colombia-0 was examined using wildtype TCV and non-pathogenic strains of Pseudomonas syringae pv. glycinea Race 4 containing virulence genes avrRpt2, avrRpm1 and avrRps4. Transgenic lines of A. thaliana that express the TCV proteins p8, p9 or CP were also examined in an attempt to determine if these proteins play a role in suppression of the HR. Crosses of these transgenic lines were made in order to determine if binary combinations of these proteins were sufficient for HR suppression. In addition, assays were completed to determine if the inhibition of the HR correlated with suppression of resistance to the virulent Pseudomonas syringae pv. maculicola ES4236 avrRpt2 growth in the plant. Finally, PR-1 protein expression was inspected by visual and quantitative GUS reporter gene assays to determine if TCV also played a role in inhibition of the plants ability to develop systemic acquired resistance (SAR).