The Region of Western Pacific Warm Pool (WPWP) is closely related to Global climate system. Previous studies indicate that the region of WPWP is affected by Walker circulation (WC) and Hadley cell (HC). WPWP expands when WC becomes stronger or when HC becomes weaker, and contracts when WC becomes weaker or when HC becomes stronger. In this study, records derived from core ODP1115B, including stable oxygen and carbon isotopes are used to reconstruct the long-term hydrological variations of WPWP over the past 2.2 Ma. We compared two species of foraminifera: Neogloboquadrina dutertrei and Globigerinoides sacculifer, for the reconstruction of differences between surface water and oceanic subsurface water. We try to find out the relationships between the thermocline depth in southern WPWP, the region of WPWP, HC and WC. However, our records indicate that the depth of thermocline in southern WPWP may be effected by the region of WPWP and the hydrology of southern WPWP. According to the Paleothermometry records of ODP806, ODP847, ODP1115 and MD063018, we can explain the relationship between WC, HC and the region of WPWP. Before 1.8 Ma, southern WPWP may not be affected by weak WC. During 1.8~1.2 Ma, WC becomes stronger and effect the region of WPWP. At the period of 1.2~0.9 Ma, southward migration of WPWP enhanced the influence of WC on the region of south WPWP and the depth of thermocline, then weakened HC in the southern hemisphere. After 0.9 Ma, the variation of hydrology in southern WPWP may be affected by stronge WC, not HC. We suggest that the influence of HC in southern WPWP is resulted in the southern region of WPWP.

The climate response of the equatorial Pacific to increased greenhouse gases is investigated using numerical experiments from five climate models participating in the Intergovernmental Panel on Climate Change Fourth Assessment Report. Changes in the heat budget of the surface layer in response to CO2 doubling (2xCO2) are analyzed in experiments with full-coupled ocean dynamics; and compared to experiments with uncoupled ocean dynamics. In full-coupled experiments, weaker ocean zonal currents driven by a slowing down of the Walker circulation reduce the ocean heat flux divergence throughout the equatorial Pacific. The resulting ocean dynamical heating enhances the surface warming due to increased clear-sky surface radiation in response to 2xCO2. The total radiative plus ocean dynamical heating are stabilized by evaporation and cloud feedbacks over the warm pool and by increased ocean vertical heat transport over the cold tongue. Increased near-surface thermal stratification enhances vertical heat transport in the cold tongue despite a reduction in vertical velocity. This ocean dynamical cooling is the dominant negative term in the heat budget changes over the eastern Pacific; and represents a strengthening of the processes leading to the annual cycle of the cold tongue, which increases by 0.4 K as a result. The stratification response is found to be a permanent feature of the equilibrium climate potentially linked to both thermodynamical and dynamical changes within the equatorial Pacific. To conclude, the relationship between the heat budget changes and the SST response is discussed along with implications for detecting these signals in the modern observational record.

This thesis documents a collection of experimental investigations in which a differentially-heated annulus was used to investigate the effects of topography on the atmospheric and oceanic circulation. To this end a number of experiments were devised, each using a different topographic base to study a different aspect of the impact of topography, motivated by the most notable outstanding questions found in a review of the literature, namely exploring the effects of topographic resonance, blocking via partial barriers, and azimuthally differential-heating via thermal topography. First of all, whilst employing sinusoidal wavenumber-3 topography to extend the experimental parameter space of a similar study, namely Read and Risch (2011), a new regime within a region of structural vacillation was encountered. Denoted as the ‘stationary-transition’ regime, it featured periodic oscillations between a dominant stationary wavenumber-3 flow and axisymmetric or chaotic flow. An investigation into topographic resonance followed, keeping the wavenumber-3 base, but with a sloped lid to add a beta effect to the annulus. This acted to increase the occurrence of stationary waves, along with the ‘stationary-transition’ regime, which was discovered to be a near-resonant region where nonlinear topographic resonant instability led to a 23 to 42 ‘day’ oscillatory structure. The base was then replaced with an isolated ridge, forming a partial barrier to study the difference between blocked and unblocked flow. The topography was found to impact the circulation at a level much higher than its own peak, causing a unique flow structure when the drifting flow and the topography interacted in the form of an ‘interference’ regime at low Taylor Numbers, as well as forming an erratic ‘irregular’ regime at higher Taylor Numbers. Lastly, this isolated ridge was replaced by flat heating elements covering the same azimuthal extent, in order to observe whether thermal topography could be comparable to mechanical topography. These azimuthally-varying heating experiments produced much the same results as the partial barriers study, despite the lack of a physical peak or bottom-trapped waves, suggesting that blocking is independent of these activities. Evidence of resonant wave-triads was noted in all experiments, though the component wavenumbers of the wave-triads and their impact on the flow was found to depend on the topography in question.

The objective of this study is to describe the effects of the El Niño-Southern Oscillation (ENSO) on the weather patterns in Queensland during the Australian summer monsoon. The focus is on the period from October-January when the summer monsoon is governing the weather pattern of Northern Australia. The theory part introduces the reader to the physics of the different phases of ENSO and the Australian summer monsoon. Weather station data of rainfall, minimum and maximum temperature data are investigated statistically. The presented results are an earlier onset of the monsoon season in Queensland during La Niña-events and a stronger monsoon in the sense of more or stronger active periods. Regarding El Niño's effects on the summer monsoon in Queensland no significant results were found. The results show the importance of not looking at the warm and cold phase of ENSO as opposites and agree with what Sarachik (2010) and Sturman & Tapper (1996) states. / Målet med studien är att beskriva El Niño-Southern Oscillations (ENSO) effekter på vädret i Queensland under den australiensiska sommarmonsunen. Fokus ligger på perioden oktober-januari då sommarmonsunen styr vädret över norra Australien. Teoridelen syftar till att introducera läsaren till fysiken bakom de olika faserna av ENSO och den australiensiska sommarmonsunen. Data från väderstationer i Queensland av parametrarna nederbörd, minimum och maximum temperatur undersöks statistiskt. Resultaten som presenteras indikerar en tidigare början av monsunsäsongen i Queensland under La Niña-perioder och att monsunen förstärks genom fler eller starkare aktiva perioder. I resultaten sågs ingen eller mycket svag påverkan från El Niño-perioder på monsunen i Queensland. Dessa resultat påvisar vikten av att inte se på den varma och kalla fasen av ENSO som motsatser till varandra och stämmer överens med litteratur av Sarachik (2010) och Sturman & Tapper (1996).