Tingzhuang Yan

Climatology and Interannual Variability of North Atlantic Hurricane Tracks

The spatial and temporal variability of North Atlantic hurricane tracks and its possible association with the annual hurricane landfall frequency along the U.S. East Coast are studied using principal component analysis (PCA) of hurricane track density function (HTDF). The results show that, in addition to the well-documented effects of the El Nino–Southern Oscillation (ENSO) and vertical wind shear (VWS), North Atlantic HTDF is strongly modulated by the dipole mode (DM) of Atlantic sea surface temperature (SST) as well as the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). Specifically, it was found that Atlantic SST DM is the only index that is associated with all top three empirical orthogonal function (EOF) modes of the Atlantic HTDF. ENSO and tropical Atlantic VWS are significantly correlated with the first and the third EOF of the HTDF over the North Atlantic Ocean. The second EOF of North Atlantic HTDF, which represents the “zonal gradient” of North Atlantic hurricane track density, showed no significant correlation with ENSO or with tropical Atlantic VWS. Instead, it is associated with the Atlantic SST DM, and extratropical processes including NAO and AO. Since for a given hurricane season, the preferred hurricane track pattern, together with the overall basinwide hurricane activity, collectively determines the hurricane landfall frequency, the results provide a foundation for the construction of a statistical model that projects the annual number of hurricanes striking the eastern seaboard of the United States.

Great Lakes Water Levels: Decomposing Time Series for Attribution

Great Lakes water levels have been trending downwards throughout the 20th and into the 21st Centuries. Potential causes are numerous. There have been dredging and water diversion projects over the last 110 years, increasing demand for fresh water consumption from a rising population, and considerable variations in environmental factors (rainfall, snowfall, air temperature and wind), all causal in nature. A thorough assessment of United States federal agency and laboratory data archives of time series of winds, air temperatures, rainfall and snowfall, and water level data, reveals that falling lake levels can be linked to rising air temperatures. Non-uniform, post-glacial, isostatic adjustments of the entire Great Lakes region has further complicated the system as land mass tilting causes localized uplift or subsidence that has also altered relative water levels. A mathematical decomposition of the various data sets and accessory calculations strongly indicate regional atmospheric temperature increases over the entire 20th century and the early 21st century resulting in increased evaporation, is the dominant driving factor in the continued downward trend of water levels in the Great Lakes. Moreover, a high degree of correlation was discovered in comparing water level in the Great Lakes with the comparable temporal variability and record length trends evident both the Global (Land and Ocean) Surface Temperature Anomaly time series and the Atlantic Multi-Decadal Oscillation. It is of note that there have been several water level events since 2013 from which the long term losses of fresh water have undergone a change and the lakes have gained fresh water. This received a great deal of attention in both the public press and a scientific newsletter and shows that there is a danger in only dealing with a small portion, 2 years, of a 120 year climate record.

On Sea Level Variability and Trends in United States Coastal Waters and Relationships with Climate Factors

Significant portions of the United States (U.S.) property, commerce and ecosystem assets are located at or near the coast, making them vulnerable to sea level variability and change, especially relative rises. Although global mean sea level (MSL) and sea level rise (SLR) are fundamental considerations, regional mean sea level (RSL) variability along the boundaries of U.S. along the two ocean basins are critical, particularly if the amplitudes of seasonal to annual to inter-annual variability is high. Of interest is that the conventional wisdom of the U.S. agencies, the National Aeronautics and Space Administration (NASA) and the National Oceanic and Atmospheric Administration (NOAA) which both contend that the sources of sea level rise are related principally to heat absorption and release by the ocean(s) to the atmosphere and vice versa, and by Polar glacier melting and freshwater input into the ocean(s). While these phenomena are of great importance to SLR and sea level variability (SLV), we assess a suite of climate factors and the Gulf Stream, for evidence of correlations and thus possible influences; though causality is beyond the scope of this study. In this study, climate factors related to oceanic and atmospheric heat purveyors and reservoirs are analyzed and assessed for possible correlations with sea level variability and overall trends on actionable scales (localized as opposed to global scale). The results confirm that oceanic and atmospheric temperature variability and the disposition of heat accumulation or the lack thereof, are important players in sea level variability and rise, but also that the Atlantic Multi-Decadal Oscillation, the El Nino-Southern Oscillation, the Pacific Decadal Oscillation, the Arctic Oscillation, the Quasi-Biennial Oscillation, the North Atlantic Oscillation, Solar Irradiance, the Western Boundary Current-Gulf Stream, and other climate factors, can have strong correlative and perhaps even causal, modulating effects on the monthly to seasonal to annual to inter-annual to decadal to multi-decadal sea level variability at the community level.

AN EMPIRICAL STUDY OF TROPICAL CYCLONE ACTIVITY IN THE ATLANTIC AND PACIFIC OCEANS: 1851–2005

The trends and intrinsic frequencies in the time series of the number of Tropical Cyclones (TCs), hurricanes and typhoons, and Categories 4 and 5 hurricanes and typhoons in the Atlantic and Pacific Ocean domains, and the yearly integral of hurricane wind energy, represented by the Power Density Index (PDI), in the Atlantic and Eastern North Pacific Ocean domains are studied. The results show that the Empirical Modal Decomposition (EMD) method [Huang et al. (1998)] successfully reveals that there are intrinsic modes of variations that are controlled by climate systems such as the Quasi-Biennial Oscillation (QBO), the El Nino Southern Oscillation (ENSO), and the Atlantic and Pacific Multi-Decadal Oscillations (AMO and PDO), along with the Meridional Overturning Circulation (MOC). It also reveals some oscillation modes whose controlling factors are not yet identified. In both the Atlantic and Pacific Ocean domains, the frequencies of TCs, hurricane/typhoon-strength TCs and the strongest (Saffir-Simpson Categories 4 and 5) TCs have slowly rising trends. In the Atlantic Ocean, our study indicates that since the mid-1970s, the observed rise in the number of the strongest (Cats. 4 and 5) TCs as discussed previously by Webster et al. [2005] and the rise in the measure of destructiveness, the Power Density Index (PDI), developed by Emanuel [2005], were not the cause of rising trends, but instead, they are the result of the combination of positive phases of several intrinsic frequency modes. In the Pacific Ocean, the rising trends have larger amplitudes than those in the Atlantic Ocean, but the higher frequency modes appear to play a more important role in deciding the year-to-year Pacific TC, hurricane/typhoon and Cats. 4 and 5 TC activity levels.

Storm Induced Water Levels In Norfolk Virginia And Chesapeake Bay: A Model And Observations

An assessment of storm induced water levels in Norfolk Virginia (VA) and Chesapeake Bay using an interactively coupled wave and current numerical model driven by a numerical atmospheric model versus actual observations is presented. The reason for the interactive coupling is that this type of model coupling has been found to greatly improve coastal inundation modeling in another coastal domain. The model system is applied in an area where coastal flooding is likely to increase in the near future and beyond, because the Norfolk VA area has been found to be a “hot spot” along the eastern seaboard as regards rising coastal water levels along the U.S. Atlantic Eastern Seaboard. To assess the variability of sea level we conducted an empirical decomposition of the Sewell’s Point water level data and found that there are eight modes of variability ranging from monthly to seasonal to annual to inter-annual to 5-7 years to 10-12 years to about 25 years, with an overall upward trend which has varied from 0.35 t0 0.85 cm/year and is presently 0.65 cm/year. As modes 1 through 7 all have separate temporal periods of oscillation it is unlikely for all seven modes to be positive or negative at any particular time, however that occurrence is a possibility, and if that were to occur, the base water level could be 20 or 35 cm or 50 cm higher. Our numerical model results are validated against National Oceanic and Atmospheric Administration (NOAA) National Weather Service (NWS) observed wind fields, and National Ocean Service (NOS) water levels and surface gravity wave significant wave field heights, collected in the Chesapeake Bay domain, show excellent agreement. Given our documented assessment of the variability of coastal water level along the southern VA coastline, future, hurricanes and winter cyclones will subject the Norfolk region to far more coastal inundation and flooding in excess and more frequently than what it has experienced in the past. Norfolk residents will very likely experience frequent “nuisance” flooding and coastal erosion during periods of even moderately strong atmospheric winds associated with the passages of typical winter storms, especially Mid-Latitude cyclones and tropical cyclones; especially during high tides.

The Role of Tibetan Plateau Snow Cover in the 1978 and 2001 WesternNorth Pacific Typhoon Seasons

An inverse correlation has been identified between the annual number of landfall typhoons along East China Seaboard (ECS) and the Tibetan Plateau snow cover (TP-SC) during the preceding winter and current spring. This correlation suggests that the Tibetan Plateau snow plays a key role in the East Asia–West Pacific regional climate system, and the system further influences typhoon track pattern off ECS. In this paper, major climatic factors accounted for the startling contrast in the number of landfall typhoons along ECS during the 1978 (2) and 2001 (7) western North Pacific (WNP) typhoon seasons were investigated. Among other climate/ocean conditions associated with typhoon activity in WNP, the preceding winter and spring TP-SC plays a crucial role to modulate the ECS landfall frequency in 1978 and 2001.