U11A-0001
An Overview of the International Best Track Archive for Climate Stewardship (IBTrACS) Project
Despite the widespread interest in best track data that describes the distribution and frequency and intensity of tropical cyclones worldwide, no central repository of such data exists. There are currently six Regional Specialized Meteorological Center's (RSMC) and five Tropical Cyclone Warning Centers (TCWC) around the world that forecast and monitor storms in each of the tropical-cyclone-prone basins and annually archive best track data: information on a storm's position, intensity, as well as other related parameters. The International Best Track Archive for Climate Stewardship (IBTrACS) is a project under the auspices of the World Data Center for Meteorology – Asheville to collect and disseminate the historical tropical cyclone best track data from all available centers, merging the disparate data sets into one comprehensive product for the user community. One of the goals of the project is for the data processing methods to remain open, such that desired user feedback on data quality is more easily collected. Also, data provenance is completely recorded so all observations and corrections, either through rigorous quality control or user feedback, may be tracked. Data are then provided in various formats given the diversity of the tropical cyclone data user community. The presentation will summarize the purpose and vision of the project, the methods used to merge the data, and a discussion of results of computed global and basin-wide tropical cyclone statistics.
U11A-0002
Regional and Temporal Variations of Summer Rainfall Influenced by Tropical Cyclone Landfall over South China
Over South China the impacts of tropical cyclone (TC) landfall on the regional and temporal variations of the total summer rainfall are investigated for the period 1957-2005. To examine its prevailing pattern, an empirical orthogonal function (EOF) analysis is applied to the summed rainfall during a typhoon season (July- October) in the 105 stations where the rainfall accompanied by TC landfalls are dominant. The first leading EOF mode displays the same sign over whole domain with an explained variance of 23.4%. The spatial distribution fluctuates on decadal timescale in connection to the TC formation in the South China Sea; active periods in early 1970s and late 1990s versus inactive periods in mid 1960s, late 1980s, and early 2000s. The second EOF mode represents a seesaw pattern between the Guangdong Province and the remaining region with an explained variance of 11.4%. This seesaw pattern is correlated to diverse TC passages toward South China, which are influenced by the northward (southward) shift of the upper-tropospheric jet stream and the corresponding development of anticyclonic (cyclonic) circulation in the lower troposphere. Interestingly, this second mode is quite similar to the first leading EOF mode of the rainfall induced by TC landfalls only. This similarity of the two EOF modes using different rainfall data demonstrates that TC movements into South China and the accompanied rainfall significantly modulate the regional variation of the summer rainfall.
U11A-0003
Pattern Classification of Tropical Cyclone Tracks over the Western North Pacific using a Fuzzy Clustering Method
This study presents the pattern classification of tropical cyclone (TC) tracks over the western North Pacific
(WNP) basin during the typhoon season (June through October) for 1965-2006 (total 42 years) using a fuzzy
clustering method. After the fuzzy c-mean clustering algorithm to the TC trajectory interpolated into 20
segments of equivalent length, we divided the whole tracks into 7 patterns. The optimal number of the fuzzy
cluster is determined by several validity measures. The classified TC track patterns represent quite different
features in the recurving latitudes, genesis locations, and geographical pathways: TCs mainly forming in
east-northern part of the WNP and striking Korean and Japan (C1); mainly forming in west-southern part of
the WNP, traveling long pathway, and partly striking Japan (C2); mainly striking Taiwan and East China (C3);
traveling near the east coast of Japan (C4); traveling the distant ocean east of Japan (C5); moving toward
South China and Vietnam straightly (C6); and forming in the South China Sea (C7).
Atmospheric environments related to each cluster show physically consistent with each TC track patterns.
The straight track pattern is closely linked to a developed anticyclonic circulation to the north of the TC. It
implies that this ridge acts as a steering flow forcing TCs to move to the northwest with a more west-oriented
track. By contrast, recurving patterns occur commonly under the influence of the strong anomalous
westerlies over the TC pathway but there definitely exist characteristic anomalous circulations over the mid-
latitudes by pattern. Some clusters are closely related to the well-known large-scale phenomena. The C1 and
C2 are highly related to the ENSO phase: The TCs in the C1 (C2) is more active during La Niña
(El Niño). The TC activity in the C3 is associated with the WNP summer monsoon. The TCs in the
C4 is more (less) vigorous during the easterly (westerly) phase of the stratospheric quasi-biennial oscillation.
This study may be applied to the statistical-dynamic long-range forecast model of TC activity as well as the
diagnostic study of TC activity.
U11A-0004
Tropical Cyclone Detection in Coral Oxygen Isotope Records
Tropical cyclones can be devastating natural disasters and long-term planning for such disasters on the part of governments and individuals would benefit greatly by knowledge of the decadal- to centennial-scale variability in tropical cyclone activity. Significant decadal and longer variations are difficult to detect in historical tropical cyclone records because the records are too short and/or non-stationary. Coral-based paleoclimate records have been suggested as possible repositories for information about previous tropical cyclone activity and this study explores the potential for corals to record the strong oxygen isotopic signature of tropical cyclone-derived precipitation. Previously published coral δ18O data from southwestern Puerto Rico spans a period that includes two hurricane landfalls in the area during the 1990s: hurricanes Georges and Hortense. The coral δ18O data show no negative δ18O anomalies during these hurricanes. The primary explanation for the absence of a signal in the coral record is an absence of a δ18O signal in the seawater for the coral to record. Given the amount of rainfall associated with these storms, typical oxygen isotopic values of tropical cyclone precipitation, and typical oxygen isotopic values of the seawater in this area, a mixing curve demonstrates that the δ18O signal of any given storm will likely be weak except in the most shallow, run-off influenced sites, i.e., sites which are sub-optimal for coral growth in the first place. Additionally, the corals must be calcifying during the event to record any geochemical signals from the seawater, but low salinities and sediment stirred up by the storm may stress the organisms, thus potentially inhibiting calcification for a short period at the time of the storm. In short, coral- based reconstructions of background climate parameters such as sea surface temperatures, long-term evaporation-precipitation balance, and ENSO may be more useful for understanding the controls on tropical cyclone activity than coral δ18O-based tropical cyclone records.
U11A-0005
The impact of tropical cyclone size on North Atlantic ACE and PDI
Climatologies of hurricane activity such as Accumulated Cyclone Energy (ACE) and Power Dissipation Index (PDI) are produced by integrating over the life cycle of the storm using maximum surface wind speeds. However, these calculations ignore the size of the tropical cyclone, which varies substantially and is independent of maximum intensity. Integrating over the size of the tropical cyclone could provide a better estimate of potential damage from a TC and can also provide a more accurate index of how tropical cyclones are responding to changes in global climate. We use two data sets of tropical cyclone size: the Extended Best Track (1988-2007) and U.S. landfall size (1920-2007). The radius of outer closed isobar is used to determine TC size in both data sets. The pressure-wind relationship model of Holland (1980) is used to provide 2-dimensional winds for each tropical cyclone. Analysis is done to compare the traditional ACE and PDI estimates (using only the maximum surface wind) with the new estimates that are integrated over the size of the tropical cyclone. Incorporation of size into the indices produces a more accurate assessment of the strength of a tropical cyclone in terms of kinetic energy and landfall impact, and is more suited for use in climate trend studies.
U11A-0006
Dynamics of the ENSO-Atlantic Hurricane Teleconnection: ENSO-related changes to the North African-Asian Jet affect Atlantic Basin Tropical Cyclogenesis
A statistical association between the El Niño-Southern Oscillation (ENSO) and the incidence of Atlantic basin hurricanes has long been observed. This correlation, in which fewer hurricanes occur during El Niño events, has generally been attributed to increases in upper tropospheric westerlies over the main development region (MDR) of Atlantic tropical cyclogenesis. However, the dynamical mechanism through which El Niño conditions increase vertical wind shear over the MDR has not been elucidated. Here we explore this teleconnection and show how changes over the equatorial Pacific, associated with ENSO, affect upper level winds over the MDR, altering the large-scale environment in which Atlantic basin hurricanes typically form. Solutions of the linearized barotropic vorticity equation indicate that two competing stationary Rossby wave responses affect shear over the MDR: canonical eastward propagating waves; and very low wavenumber westward propagating Rossby waves trapped within North African-Asian (NAA) jet. In August and September the response is dominated by the westward propagating stationary Rossby waves, which alter vorticity and upper tropospheric zonal winds over the MDR. Modeled wind anomalies are similar in pattern to observed zonal wind and vertical zonal wind shear anomalies, which suppress Atlantic-basin tropical cyclogenesis, and westward wave propagation speeds match those predicted from Rossby wave theory. By October, eastward propagating waves also develop over the tropical Atlantic Ocean in response to El Niño conditions. Over the MDR, these eastward propagating Rossby waves appear to destructively interfere with the vorticity changes produced by the westward propagating Rossby waves within the NAA jet. In addition, the NAA jet has shifted south by October. Consequently, the resultant upper tropospheric zonal wind perturbations over the MDR are weak, and suggest that ENSO should have little effect on rates of Atlantic basin tropical cyclogenesis during October. Statistical analyses of monthly ENSO-related changes in Atlantic basin tropical storm formation support these hypotheses.
U11A-0007
Stratospheric Quasi-Biennial Oscillation Signals in Tropical Cyclone Passage Over the Western North Pacific
The present study investigates the spatial distribution of tropical cyclone (TC) passages over the western North Pacific (WNP) associated with the stratospheric quasi-biennial zonal wind oscillation (QBO) for the period June-October between 1976 and 2007. A seesaw pattern of TC passages over the WNP related with the QBO phase is observed; numerous TCs are observed over the East China Sea (125°E- 130°E, 20°N-35°N) during the westerly phase of the QBO, but more TCs cross the eastern offshore of Japan (140°E-160°E, 30°N-35°N) during the easterly phase of the QBO. However, the total number of cyclone events over the WNP and the sum of the number of TCs crossing these two regions appear to be unrelated to the QBO phases. Consequently, the spatial seesaw pattern of TC passage is explained by the change in the TC movement due to an anomalous strengthening (weakening) of the subtropical North Pacific high during the westerly (easterly) phase of the QBO
U11A-0008
North Atlantic Hurricane Activity Records: 1851-2008
An analysis of hurricane data (HURDAT), using a hurricane activity index that integrates over the hurricane numbers, duration and strength during the years 1851-2008, suggests a quasi-periodic behavior with a period around 60 years superimposed upon a linearly increasing background. The periodic-like behavior is persistent in uncorrected HURDAT data as well as in data corrected for possible missing storms. The records contain two complete cycles: 1860-1920 and 1920-1980. Intense hurricane seasons of 2004, 2005 and 2008 are close to expected hurricane activity maximum to occur around the year 2010. Comparing the last 29 years (1980-2008) with the preceding 29 years (1952-1980) we find a modest increase in hurricane numbers in category 1 and 2, however, no increase in the number of major hurricanes (category 3 to 5).
U11A-0009
Tropical Cyclones and Climate Controls in the Western Atlantic Basin during the First Half of the Nineteenth Century
This study describes new comprehensive reconstructions of individual Western Atlantic Basin tropical cyclones for each year of the first half of the nineteenth century in the Western Atlantic Basin that are directly compatible and supplement the National Hurricane Center's HURDAT (Atlantic basin hurricane database). Data used for reconstructing tropical cyclones come from ship logbooks, ship protests, diaries, newspapers, and early instrumental records from more than 50 different archival repositories in the United States and the United Kingdom. Tropical cyclone strength was discriminated among tropical storms, hurricanes, major hurricanes, and non-tropical lows at least at tropical storm strength. The results detail the characteristics of several hundred storms, many of them being newly documented, and tracks for all storms were mapped. Overall, prominent active periods of tropical cyclones are evident along the western Atlantic Ocean in the 1830s but Caribbean and Gulf coasts exhibit active periods as being more evident in the 1810s and 1820s. Differences in decadal variations were even more pronounced when examining time series of activity at the statewide scale. High resolution paleoclimate and historical instrumental records of the AMO, NAO, ENSO, Atlantic SSTs, West African rainfall, and volcanic activity explain how different modes in these forcing mechanisms may explain some of the multidecadal and interannual variations. The early nineteenth century active hurricane activity appears to be particularly unique in corresponding with a low (negative index) AMO period, and as they relate to particular synoptic-scale patterns in the latter part of the Little Ice Age. Model simulations offer some hypotheses on such patterns, perhaps suggesting increased baroclinic-related storms and a slight later possible shift in the seasonal peak of tropical cyclones for some areas at times. Some years, such as 1806, 1837, 1838, 1842, and 1846 have particularly very active seasons, and we critically examined the synoptic-scale circulation responsible and also related some of the storms as they relate to potential modern analogs.
U11A-0010
Spatial Heterogeneity In The Variability Of Tropical Cyclone Climatologies For The Caribbean Basin
Historically, variations in MDR SST and ENSO have not been associated with spatially-uniform changes in topical cyclone climatologies in the Atlantic. The heterogeneous response in the Caribbean basin between 1950-2006 is examined. High-resolution estimates (1 x 1 km) of tropical cyclone climates are estimated using a novel "kernel," which takes into account several statistically parameterized structures of storms. Application of this kernel to historical data non-parametrically estimates cyclone climatologies for a number of measures and suggests a strong role for high-relief orography in setting storm climates over wide regions. Point-wise bivariate regressions of seasonal storm measures on seasonal MDR SST and annual ENSO 3.4 reveal a broadly positive influence of high MDR SST on storm intensity and frequency measures and a broadly negative influence of high ENSO 3.4 on the same measures. Bootstrapped resampling reveals regions exhibiting statistically significant associations between storm climates and these state variables. Rising MDR SST increases storm frequencies in a narrow band traversing the central basin but increases energy-release along a broader band and regions Northeast of the basin. Higher ENSO 3.4 suppresses storm frequencies and energy dissipation in the southwest of the basin, along the Central American coast and throughout the band of tracks north of the Greater Antilles. These results provide the tools for improved seasonal forecasts at sub-basin resolutions and highlight the importance of a considering spatially heterogenous responses of storm climatologies to anthropogenic climate forcing.
U11A-0011
Increase of intense storm activity during Late Holocene cold events, on the French Mediterranean Coast
Storms are one of the most alarming natural hazard due to the recent concentration of resources and
population in coastal areas. Understanding the past decadal- to millennial-scale frequency of the most
extreme events is important for assessing whether changes are controlled by climate evolution.
Understanding this intense storm variability is also important for predicting present and future community
vulnerability and economic loss. Our ability to make these assessments has been limited by the short (less
than 100 years) instrument record of storm activity. Storm-induced deposits preserved in the sediments of
coastal lagoons offer the opportunity to study the links between climatic conditions and storm activity on
longer timescales. Here we present a record of these extreme climatic events in the NW Mediterranean coast
over the Late Holocene based on sediment cores from Gulf of Lion lagoons that contain a specific
sedimentary and geochemical signature associated with intense storms.
Overwash deposits show an increase in intense storms during the latter half of the Little Ice Age and the
Holocene Rapid Climate Change events. Comparison of the sediment record with palaeoclimate records
indicates that this variability was probably modulated by atmospheric dynamics associated with variations in
the North Atlantic Oscillation. A complete understanding of the relationship between climate fluctuations,
storm activity, and the coastal response will be crucial to predicting the impacts of future climate change.
U11A-0012
Multi–model comparison of global warming impacts on tropical cyclone genesis frequency over the western North Pacific
This study examines global warming impact on tropical cyclone (TC) genesis frequency over the western North Pacific basin (Eq.-40°N, 100°E-180°) predicted by 5 coupled general circulation models that participate in the third phase of Climate Model Intercomparison Project (CMIP3), which exhibit high performance in simulating horizontal distribution of the genesis frequency under the current climate condition. TC-like disturbances are detected and counted in simulations for the 20th-century-climate experiment and global warming experiments with emission scenarios SRESA1B, A2, and B1. It is revealed that all of the 5 models project increase trends of the genesis frequency in the central North Pacific (5°-20°N, 150°E-180°; CNP) and decrease trends over South China Sea (SCS) and a region to the east of Philippines (10°-25°N, 110°-130°E). The projected increase trend over the CNP can be interpreted by analogy with interannual variability: The interannual variability of the genesis frequency in the CNP correlates significantly with ENSO indices in a manner that more TCs are observed in the CNP during El Niño phases, and most climate models project that the sea surface temperature and the large-scale circulation in the tropical Pacific would become more El Nino like with the global warming. Relative vorticity in the lower troposphere and vertical wind shear would become more favorable conditions for TC genesis in the CNP. We conclude that these two factors are major contributors to the projected increase of the genesis frequency in this region. Over the SCS, environmental conditions in the future climate are diagnosed as more favorable for TC genesis, in spite of a decrease projection of the genesis frequency. We discuss that the decrease projection over the SCS may be associated with a projected weakening of the activity of tropical depression-type atmospheric disturbances that are considered to trigger the TC genesis.
U11A-0013
Statistical Model of Tropical Cyclones in the Western North Pacific Examining Large-Scale Climate State Effects on Landfall
Evolution in landfall rates of intense tropical cyclones (TCs) is of major concern to coastal populations and policy makers. We are developing a statistical model of western North Pacific TCs to estimate the sensitivity of East-Asia landfall to large-scale climate state. The model is based on the 1951-2004 Joint Typhoon Warning Center track data. TC genesis and lysis locations are determined using kernel probably distribution functions with optimized length-scales. For TC propagation, we compute local means and variances of 6- hourly displacements using optimized averaging kernels and treat the residuals as autoregressive. We use the model to generate 1000s of stochastic realizations of the 1951-2004 period, and compare landfall rates to historical rates to assess model performance. The model components are then conditioned on basin-wide SST and ENSO, and preliminary results of landfall sensitivity are shown.
U11A-0014
Erosion of the terrestrial biosphere from mountains driven by tropical cyclones
Within the Intertropical Convergence Zone (ITCZ) tropical cyclones make landfall on tectonically active mountain islands. There, cyclones trigger floods that erode and rapidly transfer large amounts of clastic sediment to the ocean. Many of these islands are populated by tropical forest which contains large amounts of carbon in vegetation and soil. If organic carbon is eroded from the terrestrial biosphere and buried with sediment then it is a sink of atmospheric carbon dioxide. However, the role of these floods in the carbon cycle remains unsubstantiated, primarily because a significant and variable fraction of the particulate organic carbon (POC) in mountain rivers is from rock (fossil POC) i.e. not recently derived from the atmosphere. Here we use radiocarbon to quantify the source of POC in suspended sediment samples collected from the LiWu River, Taiwan, during tropical cyclone triggered floods. We find a positive non-linear relationship between water discharge and the concentration of POC derived from vegetation and soil (non-fossil POC). This elucidates a strong climatic control on the erosion of the terrestrial biosphere from mountains. During tropical cyclone triggered floods the mountain river transfers non-fossil POC rapidly with large amounts of sediment. Affecting many mountain areas within the ITCZ, tropical cyclones should optimise the delivery and burial of significant amounts of non-fossil POC derived from mountain slopes in ocean basins. The magnitude and efficiency of this carbon transfer from atmosphere to sediment is set by the frequency, intensity and duration of tropical cyclones. If these parameters are sensitive to changes in atmospheric carbon dioxide levels our findings imply a negative carbon cycle feedback between cyclone climate and the erosion of the terrestrial biosphere. This contrasts well documented positive feedbacks in the Earths climate system.
U11A-0015
A Stratigraphic Record of Tropical Cyclone Events in Low-Lying Yucatan Peninsula
Paleotempestology, the study of ancient storm events, is a field that is currently growing thanks to new techniques for identifying large storm events in climate archives. New identification methods of pre-historic storm events are beginning to impact our understanding of how tropical cyclones fit into the climate system. This research aims to create an inexpensive, first order storm identification method for stalagmites in low- lying karst regions based on clastic deposits layered within the calcite of stalagmites. Many caves in the Yucatan Peninsula are partially submerged when the water table is at its normal height. These caves flood when a large storm moves over the area when the regional water table rises a few meters for days at a time, depositing a layer of mud and debris on cave surfaces. As the water table subsides, the drip water pushes the mud from the top of the stalagmite and speleothem calcite continues to be deposited and the record of the storm is preserved as a dark mud layer. Stalagmite CH-1 was collected from the cave Chaltun-Ha outside Rancho Chaltun-Ha in the Mexican state of Yucatan. A cross section reveals sedimentary mud deposits present within the calcite layers. We will relate the mud layers to local modern storm history by layer counting and radiometric 210Pb, 137Cs, and/or U/Th dating techniques. We also tested the tropical cyclone origin of the post mud-layer calcite using an established stable isotope technique that looks for excursions in δ18O values.