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This study uses high resolution satellite measurements from the Tropical Rainfall Measuring Mission (TRMM), Quick Scatterometer (QuikSCAT) and Special Sensor Mi℗Ơcrowave Imager (SSM/I) to investigate the variability of sea surface temperature (SST), surface wind velocity, water vapor, cloud liquid water and precipitation associated with westward moving tropical instability waves (TIWs) in the Atlantic Ocean from 1998 to 2005. On interannual scales, TIWs in the Pacific Ocean are strongest during the cold phase of El Nin̈o Southern Oscillation (ENSO), when the cold tongue is most pronounced. The waves are weak during the warm phase of ENSO. A low-frequency Atlantic air-sea coupled mode influences the TIW activity in the Atlantic Ocean as ENSO does in the Pacific Ocean. The characteristics of TIWs are largely associated with the background oceanographic states. Coherent ocean-atmosphere patterns are shown in the Atlantic Ocean during eight years. Southeasterly trades strengthen and water vapor increases over warm SST anomalies associated with TIWs. The opposite is true over cold TIW SST anomalies. The cloud liquid water and rain response to the SST follows a very similar pattern, appearing to be roughly in phase with wind convergence and divergence in the central tropical Atlantic. The atmospheric response to the TIW SST anomalies extends north of the TIW active region, suggesting a remote response to the TIWs. The atmospheric response to the Atlantic TIWs shows interannual variability. In 1999, the rainfall response to the TIW SST anomalies is much larger than in other years, which is due to the southward movement of Atlantic ITCZ (Intertropical Convergence Zone). When the Atlantic ITCZ moves south, it is more susceptible to TIW influence. One regional climate model and one global climate model are applied to study the mechanism of atmospheric response to the Atlantic TIWs with daily TMI satellite SST forcing. Both models successfully simulated the wind velocity, wind convergence and precipitation as observed. While the satellite observations support the vertical mixing mechanism for the surface wind response to TIWs, both models show the pressure gradient mechanism is dominant in the Atlantic.
The unique dynamics of the equatorial oceans play an important role in the El Nino - Southern Oscillation (ENSO) and the ocean's meridional overturning circulation (MOC), both of which are critical processes that drive global climate variability on a range of time-scales. This dissertation makes a number of contributions to our understanding of equatorial ocean dynamics, lateral and vertical mixing at the equator, the behavior of equatorial waves and deep equatorial mixing, with implications for both ENSO and the MOC. The main contributions are: 1) Tropical instability waves (TIWs), the main drivers of lateral eddy mixing in the eastern equatorial Pacific, share a number of dynamical features with submesoscale flows in the mid-latitudes. In particular, their formation depends on the detailed frontal dynamics and sharp vertical gradients around their fringes, with implications for TIW energetics and the accurate representation of TIWs in low-resolution ocean models. 2) TIWs drive modulations in vertical mixing by altering the vertical shear of the Equatorial Undercurrent (EUC) through horizontal vortex stretching. This modulation can drive net sea surface cooling over the eastern Pacific cold tongue that may partially offset the warming driven by TIW lateral mixing. The magnitude of the net cooling depends on the mixing scheme used to parameterize vertical mixing, with implications for the role of TIWs in the mixed-layer heat budget in different ocean models. 3) Downwelling (upwelling) equatorial Kelvin waves can drive large decreases (increases) in the amplitude of the TIW field in the eastern equatorial Pacific and thus TIW-driven lateral and vertical mixing. The Kelvin waves alter the strength and structure of the background flow from which the TIWs gain energy, resulting in complex changes to the TIW energy budget. One major sink of TIW energy, the downward radiation of waves, is strongly altered with implications for deep and abyssal equatorial ocean circulation. 4) Mixing in the abyssal equatorial Pacific can exhibit a seafloor-intensified vertical structure even over smooth topography. The generation and breaking of lee waves over smooth topography at low latitudes is one possible mechanism that could contribute to this mixing. However, downward-propagating equatorial waves generated at the surface by TIWs or wind events could also supply energy for seafloor-intensified mixing through two possible mechanisms, wave trapping due to the horizontal component of Earth's rotation and inertial instability initiated by wave-driven displacement of fluid away from the equator. These results suggest that more attention should be devoted to measuring and understanding mixing over smooth topography in the abyssal equatorial oceans because of its potential role in the global overturning circulation.
This book contains the results of research conducted by the Marine Hydrophysical Institute of the Ukraine on the Soviet climatic RAZREZY program. Based on summaries and modelling of the in situ data, the typical seasonal response of the main hydrophysical fields of the Tropical Atlantic Ocean to seasonal wind fluctuations is described. The book also contains the kinematic structure of currents, heat and volume transport and characteristics of their seasonal and synoptic variability, as recorded during the trans-Atlantic surveys, and spectral characteristics of the intra-tropical convergence zone variability in the Tropical Atlantic Ocean.
Ocean Mixing: Drivers, Mechanisms and Impacts presents a broad panorama of one of the most rapidly-developing areas of marine science. It highlights the state-of-the-art concerning knowledge of the causes of ocean mixing, and a perspective on the implications for ocean circulation, climate, biogeochemistry and the marine ecosystem. This edited volume places a particular emphasis on elucidating the key future questions relating to ocean mixing, and emerging ideas and activities to address them, including innovative technology developments and advances in methodology. Ocean Mixing is a key reference for those entering the field, and for those seeking a comprehensive overview of how the key current issues are being addressed and what the priorities for future research are. Each chapter is written by established leaders in ocean mixing research; the volume is thus suitable for those seeking specific detailed information on sub-topics, as well as those seeking a broad synopsis of current understanding. It provides useful ammunition for those pursuing funding for specific future research campaigns, by being an authoritative source concerning key scientific goals in the short, medium and long term. Additionally, the chapters contain bespoke and informative graphics that can be used in teaching and science communication to convey the complex concepts and phenomena in easily accessible ways. - Presents a coherent overview of the state-of-the-art research concerning ocean mixing - Provides an in-depth discussion of how ocean mixing impacts all scales of the planetary system - Includes elucidation of the grand challenges in ocean mixing, and how they might be addressed
The stratified ocean mixes episodically in small patches where energy is dissipated and density smoothed over scales of centimeters. The net effect of these countless events effects the shape of the ocean's thermocline, how heat is transported from the sea surface to the interior, and how dense bottom water is lifted into the global overturning circulation. This book explores the primary factors affecting mixing, beginning with the thermodynamics of seawater, how they vary in the ocean and how they depend on the physical properties of seawater. Turbulence and double diffusion are then discussed, which determines how mixing evolves and the different impacts it has on velocity, temperature, and salinity. It reviews insights from both laboratory studies and numerical modelling, emphasising the assumptions and limitations of these methods. This is an excellent reference for researchers and graduate students working to advance our understanding of mixing, including oceanographers, atmospheric scientists and limnologists.