Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 202-212).

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (p. 124-130).

Anecdotal evidence suggests that increased numbers of waterfowl are remaining at northern latitudes throughout winter in the Mississippi Flyway. A calculated weather severity index (WSI), based on temperature and snow data, determined that local mallard abundance decreases when a WSI of 8 is reached. In mapping the WSI 8 line, mallard movement can be estimated. A fifty year trend analysis of the climatic factors driving duck migration for various locations within the Mississippi Flyway was used to determine whether climatic shifts have occurred, finding that although there are sinusoidal temperature trends throughout those years, the past decade has a longer and overall warmer trend. In examining the role of El Niño Southern Oscillation, it was found that in La Niña there is a more severe WSI, and El Niño correlates with a less severe WSI. A neutral Oceanic Niño Index caused a very high or very low WSI (was inconclusive).

This thesis aims to improve the understanding of El Niño Southern Oscillation (ENSO) diversity, in its future change, modeling and predictability. How might ENSO change in the warming climate? To reach a comprehensive understanding, a set of empirical probabilistic diagnoses (EPD) is introduced to measure the ENSO behaviors as to tropical Pacific sea surface temperature (SST) climatology, annual cycle, ENSO amplitude, seasonal phase locking, diversity in peak location and propagation direction, as well as the El Niño-La Niña asymmetry in amplitude, duration and transition. This diagnosis is applied to the observations, and consistency with previous studies indicates it is valid. Analysis of 37 CMIP5 model simulations for the 20th century and the 21st century shows that, other than the projected increase in SST climatology, changes in other aspects are largely model dependent and generally within the range of natural variation. The change favoring eastward propagating El Niños is the most robust seen in the SST anomaly field. To what extent can we trust the future projection? CMIP5 models show large spreads in terms of 20th century ENSO performance. So a data-driven approach called Empirical Model Reduction (EMR) is carried out, by fitting a low-dimensional nonlinear model from the observation with a representation of memory effect and seasonality. The stochastic simulation of EMR is able to reproduce a realistic ENSO diversity statistics and a reasonable range of natural variation, thus provides an additional benchmark to evaluate the CMIP5 model biases. What are the key model components leading to a good performance to simulate and predict ENSO? Using a suite of models under the aforementioned framework of EMR, control experiments are conducted to advance the understanding of ENSO diversity, nonlinearity, seasonality and the memory effects. Nonlinearity is found necessary to reproduce the ENSO diversity features by simulating the extreme El Niños. Nonlinear models reconstruct the skewed distribution of SST anomalies and improve the prediction of the El Niño-La Niña transition. Models with periodic terms reproduce the SST seasonal phase locking but do not improve the prediction appreciably. Models representing the ENSO memory effect, based on either the recharge oscillator (multivariate model with tropical Pacific subsurface information) or the time-delayed oscillator (multilevel model with SST history information), both improve the prediction skill dramatically. Models with multiple ingredients capture several ENSO characteristics simultaneously and exhibit overall better prediction skill. In particular, models with a memory effect show an alleviated skill drop during the spring barrier and a reduced prediction timing delay. One new ENSO prediction target is to predict not only the occurrence and amplitude of El Niño (EN) but also the peak location is at the central Pacific (CP) or the eastern Pacific (EP). Many prediction models have difficulty with it, which motivates the investigation on whether such ENSO diversity has intrinsically limited predictability. Here three aspects are addressed including the source/limit of predictability, time range and uncertainty. Approaches are combined including linear inverse modeling, singular vector analysis and probabilistic measure. The results show that two similar initial conditions with western Pacific SST warming anomalies may finally develop to either CPEN or EPEN. The equatorial Pacific subsurface evolution is important to tell the final outcome. Restricted by the chaotic property, the prediction horizon appears to be ~4 months before CPEN and ~7 months before EPEN. A flavor prediction model using data's transition probabilities is introduced as a new benchmark for probabilistic prediction.

The El Niño – Southern Oscillation (ENSO) has far-reaching impacts across the globe and provides the most reliable source of seasonal to interannual climate prediction over North America. Though numerous studies have discussed the impacts of ENSO teleconnections on North America during boreal winter, it is becoming more and more apparent that the regional impacts of ENSO teleconnections are highly sensitive to the seasonal evolution of ENSO events. Also, the significant impacts of ENSO are not limited to the boreal winter seasons. To address these knowledge gaps, this thesis examines the seasonal dependence of ENSO teleconnections and impacts on North American surface climate, focusing on two examples. Chapter 1 examines the relationship between El Niño – California winter precipitation. Results show that the probability of the anomalous statewide-wetness increases as El Niño intensity increases. Also, the influences of El Niño on California winter precipitation are statistically significant in late winter (Feb-Apr), but not in early winter even though that is when El Niño usually reaches its peak intensity. Chapter 2 further investigates why the strong 2015/16 El Niño failed to bring above normal winter precipitation to California, focusing on the role of westward shifted equatorial Pacific sea surface temperature anomalies (SSTAs) based on two reasons: the maximum equatorial Pacific SSTAs was located westward during the 2015/16 winter compared to those during the 1982/83 and 1997/98 winters, both of which brought extremely wet late winters to California. Also, the North American Multi-Model Ensemble (NMME) forecasts overestimated the eastern tropical Pacific SSTAs and California precipitation in the 2015/16 late winter, compared to observations. The Atmospheric General Circulation Model (AGCM) experiments suggested that the SST forecast error in NMME contributed partially to the wet bias in California precipitation forecast in the 2015/16 late winter. However, the atmospheric internal variability could have also played a large role in the dry California winter during the event. ENSO also exerts significant impacts on agricultural production over the Midwest during boreal summer. Chapter 3 examines the physical processes of the ENSO summer teleconnection, focusing on the summer when a La Niña is either transitioning from an earlier El Niño winter or persisting from an existing La Niña winter. The results demonstrate that the impacts are most significant during the summer when El Niño is transitioning to La Niña compared to that when La Niña is persisting, even though both can loosely be defined as developing La Niña summer. During the transitioning summer, both the decaying El Niño and the developing La Niña induce suppressed deep convection over the tropical Pacific and thereby the corresponding Rossby wave propagations toward North America, resulting in a statistically significant anomalous anticyclone over northeastern North America and, therefore, a robust warming signal over the Midwest. These features are unique to the developing La Niña transitioning from El Niño, but not the persistent La Niña. In Chapter 4, we further evaluate the performance of NCAR CAM5 forced with historical SSTA in terms of the La Niña summer teleconnections. Though the model ensemble mean well reproduces the features in the preceding El Niño/La Niña winters, the model ensemble mean has very limited skill in simulating the tropical convection and extratropical teleconnections during both the transitioning and persisting summers. The weak responses in the model ensemble mean are attributed to large variability in both the tropical precipitation, especially over the western Pacific, and atmospheric circulation during summer season. This thesis synthesizes the physical processes and assessments of climate models in different seasons to establish the sensitivity of regional climate to the seasonal dependence of ENSO teleconnections. We demonstrate that the strongest impacts of ENSO on North American regional climate might not be necessarily simultaneous with maximum tropical Pacific SST anomalies. We also emphasize the importance of the multi-year ENSO evolutions when addressing the seasonal impacts on North American summertime climate. The findings in this thesis could benefit the improvement of seasonal hydroclimate forecasting skills in the future.

Collm (52°N, 15°E) midlatitude mesosphere/lower thermosphere (MLT) zonal winds are investigated with respect to a possible influence of the Southern Oscillation (SO). It is found that in winter the prevailing wind is positively correlated with the Southern Oscillation index (SOI), which qualitatively fits to the response of the low-latitude stratosphere on the SO. In summer, however, there is a negative correlation between MLT zonal winds and SOI. A possible mechanism, which includes slightly enhanced planetary wave propagation to the MLT in summers of low SOI is discussed. / Windmessungen aus Collm (52°N, 15°E) wurden hinsichtlich eines möglichen Einflusses der Southern Oscillation (SO) in ihnen untersucht. Es zeigt sich, dass im Winter der mittlere Zonalwind positiv mit dem \'Southern Oscillation Index\' SOI korreliert ist, was qualitativ mit der Reaktion der Stratosphäre auf ENSO übereinstimmt. Im Sommer findet sich jedoch ein negativer Zusammenhang zwischen hochatmosphärischem Zonalwind und SOI. Ein möglicher Mechanismus, der die Ausbreitung planetarer Wellen beinhaltet, wird diskutiert.

published_or_final_version / Environmental Management / Master / Master of Science in Environmental Management

A simple atmosphere and ocean model of relevance to El Nino and Southern Oscillation (ENSO) is discussed. Both the atmosphere and ocean models are two layer, three dimensional, linear and baroclinic, and generally follow the Oregon State University coupled general circulation model. However, the parameterization differs considerably from previous work in the treatment of the atmospheric latent heat release. This new parameterization follows the formula used in the theory of conditional instability of the second kind (CISK). In this the latent heat release is proportional to the low level convergence. Utilizing the "Comprehensive Ocean Atmosphere Data Set" (COADS), which contains all oceanic and atmospheric surface variables over the global ocean from 1946-1979, experimental model results are discussed for determination of the validity of the parameterizations. In particular, the years 1957, 1965 and 1972 in which El Nino events occurred are examined. The parameterization is deemed to be realistic, and should permit simulation of the El Nino upon coupling the two models. / Graduation date: 1988

For the purpose of investigating the fundamental nature of the interannual oscillation observed in the tropical Pacific in conjunction with El Nino/Southern Oscillation (ENSO), the Comprehensive Ocean Atmosphere Data Set was analyzed. Based upon this analysis, an "intermediate" tropical atmosphere-ocean coupled model was developed. For reason of their particular importance to atmosphere-ocean interactions, moisture processes such as condensation-convergence, evaporation-sea surface temperature and evaporation-wind feedbacks were given special emphasis in both the data analysis and modeling processes. The atmospheric component of the model is based on the first baroclinic mode, which is driven by the atmospheric internal heating. The oceanic model consists of two layers with an imbedded oceanic mixed-layer, by which SST is predicted. The present study has demonstrated that despite the structural simplicity of the oceanic model, it is capable of simulating mean oceanic circulation. In preparation for coupling, individual models were first tested with the use of appropriate time-dependent boundary conditions specified from the composite ENSO data. Both model simulations reproduced the major features associated with the ENSO events. Coupling was performed following the imposition of wind stress anomalies over the western Pacific for a given time period and the removal of all external forcing for a period of eight years thereafter. The coupled responses simulated during the the first two-year period provided reasonable simulations of the following ENSO-like features: the appearance of warm sea-surface temperature anomalies in the central Pacific, deepening/shallowing of mixed-layers in the eastern/western Pacific, weakening of the trades in the central Pacific, strengthening/weakening of the North Equatorial Counter Current/South Equatorial Currents, and enhanced convective activities around the dateline. The long-term coupled integration showed a pattern of interannual oscillation over a period of approximately three years. The results obtained from this coupling study have illustrated (1) that the necessary condition for the interannual oscillation is the interaction between the atmosphere and the ocean and (2) that it is likely that oceanic wave dynamics plays a crucial role in the determination of the growth and decay of ENSO events. / Graduation date: 1991

The ocean reanalysis Simple Ocean Data Assimilation (SODA) 2.2.4 is used to explore the changes in upwelling from normal conditions to either El Nino or La Nina conditions. Physical and thermodynamic variables from the reanalysis are used to explore the structure and behavior of El Nino Southern Oscillation (ENSO) events. The results of this analysis show that sea surface temperature (SST), entrainment velocity, wind stress, mixed layer depth, wind curl, and heat content anomalies are in general agreement with ENSO theory. Interestingly, the distribution of upwelling based on the entrainment velocity is very patchy, which led us to explore zonal and meridional sections of vertical velocity. We used three methods to compute changes in upwelling during ENSO events. The first method computes upwelling within the areas of SST anomalies during ENSO events. During El Nino events upwelling shows prominent decadal variability, while during La Nina the decadal variability is weaker. A new upwelling index is used for the second method, and upwelling is computed in the areas of strong upwelling anomalies. The variability of upwelling is higher in periods of reduced upwelling than in periods of strong upwelling. Despite the fact that the new index is computed independently, it agrees in the timing of the index used to define ENSO events for this research. The first and second methods show that the amplitude of SST anomalies and upwelling anomalies do not have a direct relationship, suggesting that upwelling does not explain all of the variance in SST. The last method used is to compute changes in upwelling in the Nino 1+2 region during ENSO events. In the east Pacific there is almost no correlation between upwelling and SST anomalies during ENSO, but this might be attributed to the fact that the Nino 1+2 region is a relatively small region compared to the Nino 3.4 region that is used to define ENSO events. In general, the time series of SST and upwelling anomalies agree well just in the cases when ENSO events are prominently in the eastern Pacific. A comparison between yearly fisheries data from Ecuador and Peru and monthly data of SST anomalies during ENSO years is presented showing that during El Nino events the fish catch decreases and during La Nina events the fish catch increases. We infer that the increase or decrease in fish catch is associated to changes in fish populations, and that these changes are mainly due to availability of nutrients and changes in temperature during ENSO events.