The Madden-Julian Oscillation (MJO) is the dominant mode of intraseasonal variability in the tropical atmosphere and provides global predictability on timescales that bridge the gap between weather and climate. The influence of the MJO on the ocean is explored with a combination of statistical analysis of observations using multivariate time series techniques, dynamical theory, and general circulation models with realistic forcing and bathymetry. The MJO is shown to have a significant and predictable influence on global sea level. Three main regions of influence are identified: (i) the equatorial Pacific and the west coast of the Americas, (ii) the Gulf of of Carpentaria, and (iii) the northeastern Indian Ocean. In the equatorial Pacific, equatorially trapped Kelvin waves are forced by MJO-related surface winds in the western Pacific and propagate eastward. These remotely forced waves then transform into coastal trapped waves that propagate poleward along the west coast of the Americas (consistent with previous work). By way of contrast, in the Gulf of Carpentaria it is shown that the connection with the MJO is due to local wind forcing through simple set-up of sea level. In the northeastern Indian Ocean, a complex sea level pattern involving equatorially trapped Kelvin waves, coastal trapped waves along Sumatra, Java and the Bay of Bengal, and reflected Rossby waves along 5.5$^\circ$N is shown to be caused by a combination of local and remote forcing by MJO-related surface winds. To examine the predictability of the MJO, and the stability of MJO variability on multidecadal time scales, the MJO index is reconstructed over the last century. The reconstructed index is verified by comparing it with independently observed environmental variables. Three predictability time scales are proposed and estimated from the MJO index. A simple forced damped harmonic oscillator model is used to explain the complex relationship amongst the predictability time scales and also gain insight into the predictability of the MJO.

The Madden-Julian Oscillation (MJO) has been associated with extreme precipitation events in western North America. However, the mechanisms for, and predictability of, these associations are not clear. We have examined the influence of the MJO on North Pacific - North America (NPNA) circulation and precipitation anomalies during the boreal winter. We constructed composites of MJO events during 1979-2005 determined from the Wheeler RMM1/RMM2 index of MJO activity. Our analyses of NPNA anomalies were based primarily on the National Centers for Environmental Prediction reanalysis data set. We focused our investigations on the impacts on NPNA circulation and precipitation of: (1) the location and amplitude of the convective and subsidence components of the MJO; (2) the season of MJO occurrence; and (3) concurrent El Nino (EN) or La Nina (LN) events. We found that the NPNA response to the MJO is sensitive to the location of both the convective and subsidence components of the MJO, the season of MJO occurrence, and to the existence of concurrent EN or LN events. EN or LN events affect the extratropical response to the MJO by altering the equatorial Rossby-Kelvin wave response to the components of the MJO. This in turn affects the anomalous extratropical wave trains initiated by the MJO, and alters the strength and location of the resulting NPNA precipitation anomalies. Our results have allowed us to identify characteristic patterns associated with the MJO that can be related to the location and intensity of extreme NPNA precipitation. MJO events are relatively persistent phenomena. Thus, increased understanding of the mechanisms by which they impact the extratropics has the potential to improve extratropical extended range forecasting. Our results provide a substantial foundation for improving forecasts of NPNA circulation and precipitation.

The impact of the Madden Julian Oscillation (MJO), a major source of intraseasonal variability in the tropical atmosphere, on the Indonesia Seas is investigated using satellite-derived, reanalysis and mooring data. The MJO footprint on the Indonesian Seas is evident from the surface layer into the pycnocline. In the surface, MJO air-sea heat fluxes govern the intraseasonal sea surface temperature (SST) variations. Within the pycnocline, the MJO reduces the transfer of the Pacific water to the Indian Ocean, the Indonesian Throughflow (ITF). In addition to the ocean’s response, the oceanic feedback to the MJO is also examined. Warmer SST in the Indonesian Seas during the suppressed phase of the MJO promotes the MJO convective phase to propagate eastward over the maritime continent (MC). Intraseasonal SST variation accounts for 55 - 60% of the total non-seasonal SST variance across the Indonesian Seas. It is most energetic in Banda and Timor Seas, with its standard deviation varying between 0.4 – 0.5°C. Coupled to the MJO surface fluxes, the intraseasonal SST exhibits stronger variation in boreal winter than in summer. A slab ocean model indicates that MJO surface heat fluxes account for 69-78% of the intraseasonal SST variability. The SST increases by 1.1° - 2°C, on average, in response to intense surface heating and weak winds over the suppressed (dry) MJO phase, and then decreases by 1.8° - 2.1°C over the course of the ensuing MJO active phase that is characterized by enhanced convective cooling and westerly wind bursts. Intraseasonal variability is also significant in the Sulawesi Sea SST, but it is mostly derived from eddies and local winds. Over the period 1980 - 2012, we observe 86 significant MJO (Real-time Multi variate MJO index > 1) events occurring in the Indian Ocean, of which 51 events achieve eastward propagation (EP) over the MC, while 35 events attentuate in the eastern Indian Ocean, or show no propagation (NP) over the MC. Eastward propagation (EP) MJO events occur more frequently during La Niña years than during El Niño years. Analyses of SST across the Indonesian Seas during the suppressed phase of the MJO events indicate that the SST in Java, Banda, and Timor Seas attributed to the EP MJO events is warmer by 0.5oC that associated with the NP MJO events. The warmer SST corresponds with enhanced surface latent heat flux, sensible heat flux, and low-level moisture in the atmospheric boundary layer, driven by diurnal activity. The EP MJO events are more frequent during La Niña, as the SST response to MJO events is influenced by the thermocline depth: shallower thermocline during El Niño enables cooler subsurface water under the MJO forcing to reduce SST that then attenuates MJO activity, with deeper thermocline of La Niña having the opposite outcome. Moored velocity data in Makassar Strait between 2004 – August 2011 and August 2013 – August 2015 document substantial direct impacts of the MJO on the ITF, particularly with the surface layer (< 80 m ). A composite of the along-strait velocity within the surface layer for 10 MJO events observed during the observational period exhibits strong northward velocity within days, following the peak of MJO wind stress. The MJO forces both northward along-strait pressure gradient and the resultant of northward wind stress and turbulent stress at the base of the surface layer that, together with the seasonal forcing, maintain the reduction or even reversal of the ITF southward transport on timescales of 1-3 months during boreal winter.

Intense atmospheric convection associated with the South Pacific Convergence Zone (SPCZ) significantly impacts basin-scale circulation patterns over the Pacific. We explore dynamical processes which foster changes in convection along the convergence zone. These forcings include strong moisture convergence and accumulation of wave energy in the boundary layer, as well as dynamical instability associated with moderate cross-equatorial wind bursts. A focus is applied to observing the dominant modes of variability on synoptic to intraseasonal timescales using a combination of satellite observations and NCEP reanalysis data. Accumulation of energy, due to negative stretching deformation, occurs with both tropical and extratropical modes suggesting that the SPCZ is an artifact of wide ranging modes. Signals of the dominant modes (inferred from fields of outgoing longwave radiation: OLR) are isolated using bandpass filtering techniques, which are then mapped in space and time using Principal Components from Empirical Orthogonal Function analyses. Variability of convective systems in the SPCZ is found to be significantly correlated with changes in the regional Hadley Circulation and the Pacific Walker cell. This co-variability presents the possibility of important teleconnection routes between the tropical West and East Pacific, as well as with the mid-latitude regions of the Northern and Southern Hemispheres. We test these interaction hypotheses by developing composites of the circulation patterns using dates of maximum convection events (regions of minimum OLR) in the SPCZ. Intensities of the large-scale circulations are measured using observations of stream function mass fluxes. Results suggest that deep convection maxima (minima) are associated with an increase (decrease) in the Walker Circulation. It is also illustrated how off-equatorial convection anomalies in the subtropical portion of the SPCZ may induce changes to the Hadley Circulation. Interactions with the zonal (Walker) and meridional (Hadley) circulations appear to have important consequences on the ability for wave energy to propagate through the tropical Pacific atmosphere. Examples include Northern Hemisphere cross-equatorial teleconnections through the Westerly Wind Duct in the upper branch of the Walker circulation and Rossby wave trains in the SPCZ, which may be partially governed by characteristics of the regional Hadley circulation.

The continental shelf on the western side of the Antarctic Peninsula is a region of substantial climate and ecosystem change. The Long Term Ecological Research project at Palmer Station has been sampling and studying the shelf ecosystem and physical environment since 1990. This dissertation seeks to improve our understanding of the subtidal and intraseasonal (hereafter defined together as 3-100 days) circulation on the neighboring continental shelf and is particularly motivated by the aims of the project to understand (1) how lateral transports of scalar parameters such as heat affect the vertical stratification and (2) how coastal canyon heads are linked to the larger-scale shelf circulation and why they are such ecologically productive environments. In this dissertation we study: (1) the origin and mixing of mesoscale eddies as agents of heat transport and stirring; (2) the spatial coherence of shelf-scale barotropic velocity fluctuations, their origin through flow-topography interaction with Marguerite Trough Canyon, and their associated heat transports; and (3) the wind-driven dynamics of the long-shore flow manifested through coastal trapped waves and their ability to both induce upwelling at a coastal canyon head and to modulate isopycnal depth at the continental shelf-break. This work takes an observational approach, utilizing the rare and expansive data set afforded by the long-term sampling program including shipboard CTD and ADCP profiles, moored current meter time series, and CTD profiles from an autonomous underwater vehicle.

The Madden-Julian Oscillation is a tropical atmospheric phenomenon detected as anomalies in zonal winds, convection and cloudiness. This perturbation has a definitive timescale of about thirty to sixty days, allowing its signal to be extracted from background data. The Madden-Julian Oscillation originates over the western Indian Ocean and generates a convective region which moves east along the equatorial region. This perturbation is thought to contribute to the timing and intensity of the eastern hemisphere monsoons, the El Niño/ Southern Oscillation and tropical storms and cyclones. The current understanding of the Madden-Julian Oscillation is that it restricts the bulk of its' influence to the tropics, however some evidence suggested that the impact is more extensive. Analysis of about 30 years of data showed significant modulation of rainfall by the equatorial passage of the MJO. The real-time multivariate Madden-Julian Oscillation Index was used to estimate the location and amplitude of the Madden-Julian Oscillation, and forms the basis of the basic rainfall prediction tool developed. The method developed here clearly linked the low latitude passage of the Madden-Julian Oscillation with suppressed and enhanced rainfall events in the Australasian region and beyond. A rudimentary forecasting capability at the intraseasonal time scale has been developed suitable for assisting Australian agricultural sector. A subsequent and independent analysis of global mean sea level pressure anomalies provided evidence of teleconnections between the Madden-Julian Oscillation and higher latitude atmospheric entities. These anomalies confirm the existence of teleconnections capable of producing the rainfall pattern outputs. The MJO is strongly influenced by the season. However the seasonally dependant analysis of rainfall with respect to the Madden Julian Oscillation conducted was inconclusive, suggesting aspects of the MJO influence still require clarification. Considering the importance of rainfall variability to the Australian agricultural sector the forecasting tool developed, although basic, is significant.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 130-136).

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 77-83). Also available on the World Wide Web.

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (p. 123-131).

The Madden-Julian oscillation (MJO) and the quasi-biennial oscillation (QBO) are two key modes of variability in the tropical atmosphere. The MJO, characterized by propagating, planetary-scale signals in convection and winds, is the main source of subseasonal variability and predictability in the tropics. The QBO is a ~28-month cycle in which the tropical stratospheric zonal winds alternate between easterly and westerly regimes. Via thermal wind balance these winds induce temperature anomalies, and both wind and temperature signals reach the tropopause. Recent observational results show a remarkably strong link between the MJO and the QBO during boreal winter: the MJO is stronger and more predictable when QBO winds in the lower stratosphere are easterly than when winds are westerly. Despite its important implications for MJO theory and prediction, the physical processes driving the MJO-QBO interaction are not well-understood. In this thesis, we use a hierarchy of models – including a cloud-resolving model, a forecast model, and a global climate model – to examine whether models can reproduce the MJO-QBO link, and better understand the possible mechanisms driving the connection. Based in part on our modeling findings, we further explore observed QBO temperature signals thought to be important for the MJO-QBO link. After providing necessary background and context in the first two chapters, the third chapter looks at the MJO-QBO link in a small-domain, cloud-resolving model. The model successfully simulates convection associated with two MJO events that occurred during the DYNAMO field campaign. To examine the effect of QBO, we add various QBO temperature and wind anomalies into the model. We find that QBO temperature anomalies alone, without wind anomalies, qualitatively affect the model MJO similarly to the observed MJO-QBO connection. QBO wind anomalies have no clear effect on the modeled MJO. We note however that the MJO response is quite sensitive to the vertical structure of the QBO temperature anomalies, and for realistic temperature signals the model response is very small. In the fourth chapter, we look at the MJO-QBO link in a state-of-the-art global forecast model with a good representation of the MJO. We conduct 84 hind-cast experiments initialized on dates across winters from 1989-2017. For each of these dates, we artificially impose an easterly and a westerly QBO in the stratospheric initial conditions, and examine the resulting changes to the simulated MJO under different stratospheric states. We find that the effect of the QBO on the model MJO is of the same sign as observations, but is much smaller. A large sample size is required to capture any QBO signal, and tropospheric initial conditions seem more important than the stratosphere in determining the behavior of the simulated MJO. Despite the weak signal, we find that simulations with stronger QBO temperature anomalies have a stronger MJO response. In the fifth chapter, we conduct experiments in recent versions of a NASA general circulation model. We find that a version with a high vertical resolution generates a reasonable QBO and MJO, but has no MJO-QBO link. However, this model has weaker-than-observed QBO temperature anomalies, which may explain the lack of an MJO impact. To explore this potential bias, we impose the QBO by nudging the model stratospheric winds towards reanalysis, leading to more realistic simulation of QBO temperature anomalies. Despite this, the model still fails to show a strong MJO-QBO link across several ensemble experiments and sensitivity tests. We conclude with discussion of possible reasons why the model fails to capture the MJO-QBO connection. The sixth chapter examines QBO temperature signals in a range of observational and reanalysis datasets. In particular, we are motivated by two elements of the MJO-QBO relationship which are especially puzzling: the seasonality (i.e. that the MJO-QBO link is only significant in boreal winter) and long-term trend (i.e. that the MJO-QBO link seems to have only emerged since the 1980s). By examining QBO temperature signals around the tropopause, we highlight changes to the strength and structure of QBO temperature anomalies both in boreal winter and in recent decades. Whether these changes are linked to the MJO-QBO relationship, and what more generally might explain them, is not presently clear. Overall, we demonstrate that capturing the MJO-QBO relationship in a variety of models is a difficult task. The majority of evidence indicates that QBO-induced temperature anomalies are a plausible pathway through which the QBO might modulate the MJO, but the theoretical description of precisely how these temperature anomalies may impact convection is lacking and likely more nuanced than the literature to date suggests. Most models show only a weak modulation of the MJO associated with changes in upper-tropospheric temperatures, and even when those temperature signals are artificially enhanced, comprehensive GCMs still fail to show a significant MJO-QBO connection. Our observational study indicates that temperature anomalies associated with the QBO show striking modulations on various timescales of relevance to the MJO-QBO link, but do not conclusively demonstrate a clear connection to the MJO. This difficulty simulating a strong MJO-QBO connection suggests that models may lack a key process in driving the MJO and coupling the tropical stratosphere and troposphere. It is further possible that the observed link may be in some regards different than is currently theorized -- for example statistically not robust, due to non-stratospheric processes, or driven by some mechanism that has not been suitably explored.