Simulation of the Recent Multidecadal Increase of Atlantic Hurricane Activity Using an 18-km-Grid Regional Model (original) (raw)

On Estimates of Historical North Atlantic Tropical Cyclone Activity*

Journal of Climate, 2008

In this study, an estimate of the expected number of Atlantic tropical cyclones (TCs) that were missed by the observing system in the presatellite era (between 1878 and 1965) is developed. The significance of trends in both number and duration since 1878 is assessed and these results are related to estimated changes in sea surface temperature (SST) over the "main development region" ("MDR"). The sensitivity of the estimate of missed TCs to underlying assumptions is examined. According to the base case adjustment used in this study, the annual number of TCs has exhibited multidecadal variability that has strongly covaried with multidecadal variations in MDR SST, as has been noted previously. However, the linear trend in TC counts is notably smaller than the linear trend in MDR SST, when both time series are normalized to have the same variance in their 5-yr running mean series. Using the base case adjustment for missed TCs leads to an 1878-2006 trend in the number of TCs that is weakly positive, though not statistically significant, with p ϳ 0.2. The estimated trend for 1900-2006 is highly significant (ϩϳ4.2 storms century Ϫ1 ) according to the results of this study. The 1900-2006 trend is strongly influenced by a minimum in 1910-30, perhaps artificially enhancing significance, whereas the 1878-2006 trend depends critically on high values in the late 1800s, where uncertainties are larger than during the 1900s. The trend in average TC duration (1878-2006) is negative and highly significant. Thus, the evidence for a significant increase in Atlantic storm activity over the most recent 125 yr is mixed, even though MDR SST has warmed significantly. The decreasing duration result is unexpected and merits additional exploration; duration statistics are more uncertain than those of storm counts. As TC formation, development, and track depend on a number of environmental factors, of which regional SST is only one, much work remains to be done to clarify the relationship between anthropogenic climate warming, the large-scale tropical environment, and Atlantic TC activity.

Global warming and hurricane intensity and frequency: The debate continues

The recent destruction due to hurricanes and the apparent increase in frequency in the southeastern United States, especially in 2005 season, has prompted many scientists to study possible causes of these changes. Some scientists believe that global warming and increased sea surface temperatures are to blame. Warm water holds more energy to fuel hurricanes and may contribute to the conditions needed for the formation of hurricanes. The increased ocean tempera- tures may cause a decrease in wind shear and an increase in evaporation and atmospheric water vapor. These factors all contribute to the conditions conducive to formation of hurricanes. Some scientists, however, simply believe that the recent increases are due to normal multidecadal oscil- lations resulting from currents and Thermohaline Circulation. Whereas others believe that a change in the instrumentation and data collection techniques has led to unreliable data and the creation of trends that do not exist. Although some f...

Last Millennium Hurricane Activity linked to Endogenous Climate Variability

Research Square (Research Square), 2023

Although Atlantic hurricane risk is expected to increase in a warming climate, projecting trends in hurricane frequency over the present century is still highly uncertain. The short instrumental record limits our understanding of hurricane activity and its relationship to climate, especially on multi-decadal and longer time scales. Here we extend the instrumental hurricane frequency record using two independent sources of information: (1) a reconstruc-1 tion of basin-wide Atlantic hurricane frequency over the last millennium, developed from sedimentary paleohurricane records; (2) a statistical model of hurricane activity using sea surface temperatures (SSTs) from the Last Millennium Reanalysis (LMR) datasets. We find statistically significant agreement between the two estimates, suggesting that a robust climate signal of hurricane frequency over the past millennium can be captured from proxy data. Neither estimate of hurricane frequency indicates that the late 20th century hurricane frequency is outside the range seen over the past millennium. Numerical simulations using a hurricane-permitting climate model suggest that hurricane activity over the last millennium was likely driven by endogenous climate variability and linked to anomalously warm SSTs over the Atlantic Main Development Region (MDR) as well as cold phases of Interdecadal Pacific Oscillation (IPO) SSTs. The forced signal estimated from the Last Millennium Ensemble (LME) project suggests that volcanic eruptions can induce peaks in hurricane activity, but such peaks would likely be too weak to be detected from reconstruction records due to large endogenous variability.

Hurricane track variability and secular potential intensity trends

Climatic Change, 2009

Sea surface temperature in the tropical North Atlantic has been shown to co-vary with hurricane activity on a broad range of time-scales. One general hypothesis for this observed relationship is based on the theory of potential intensity (PI) whereby the local ambient environment determines the maximum intensity that a hurricane can achieve. Under this theory, climate change and resultant changes in PI can affect the distribution of hurricane intensities by modulating the upper extreme values. Indeed, PI averaged over the tropical North Atlantic during the hurricane season has been increasing in concert with sea surface temperature, which introduces an expectation for a secular upward shift in the distribution of hurricane intensities. However, hurricane tracks also largely determine the local storm-ambient environment and thus track variability introduces additional ambient PI variability. Here we show that this additional variance removes the observed secular trend in mean summertime tropical North Atlantic PI, and there is no tacit expectation that hurricanes have become stronger based solely on PI theory. The observed trends in integrated metrics such as hurricane power dissipation are then more likely to be caused by changes in storm frequency and duration due to broader scale regional variability than secular intensity changes due solely to ambient thermodynamics.

Replicating annual North Atlantic hurricane activity 1878-2012 from environmental variables

Journal of Geophysical Research: Atmospheres

Statistical models can replicate annual North Atlantic hurricane activity from large-scale environmental field data for August and September, the months of peak hurricane activity. We assess how well the six environmental fields used most often in contemporary statistical modeling of seasonal hurricane activity replicate North Atlantic hurricane numbers and Accumulated Cyclone Energy (ACE) over the 135 year period from 1878 to 2012. We find that these fields replicate historical hurricane activity surprisingly well, showing that contemporary statistical models and their seasonal physical links have long-term robustness. We find that August-September zonal trade wind speed over the Caribbean Sea and the tropical North Atlantic is the environmental field which individually replicates long-term hurricane activity the best and that trade wind speed combined with the difference in sea surface temperature between the tropical Atlantic and the tropical mean is the best multi-predictor model. Comparing the performance of the best single-predictor and best multi-predictor models shows that they exhibit little difference in hindcast skill for predicting long-term ACE but that the best multipredictor model offers improved skill for predicting long-term hurricane numbers. We examine whether replicated real-time prediction skill 1983-2012 increases as the model training period lengthens and find evidence that this happens slowly. We identify a dropout in hurricane replication centered on the 1940s and show that this is likely due to a decrease in data quality which affects all data sets but Atlantic sea surface temperatures in particular. Finally, we offer insights on the implications of our findings for seasonal hurricane prediction. Plain Language Summary Many universities, government agencies and private companies issue seasonal outlooks for North Atlantic hurricane activity. However, the longer-term historical robustness of these models and their skill is unknown. Clarity on this matter is desirable because current seasonal hurricane outlooks are built on data which extend back, at best, only to the 1950s, and because predictors which are identified from data which span only a few decades can sometimes later fail. Here we assess how well annual North Atlantic hurricane activity is replicated over an extended 135-year period from 1878 to 2012; this by using statistical models and the large-scale environmental fields used most often in contemporary statistical modeling of seasonal hurricane activity. We find that these environmental fields replicate historical hurricane activity surprisingly well, showing that contemporary statistical models and their seasonal physical links have long-term robustness. We find that trade wind speed over the Caribbean Sea and the tropical North Atlantic is the environmental field which individually replicates long-term hurricane activity the best. We identify a dropout in hurricane replication centered on the 1940s and show that this is likely due to a decrease in data quality which affects all data sets but Atlantic sea surface temperatures in particular.

Simulated reduction in Atlantic hurricane frequency under twenty-first-century warming conditions

Nature Geoscience, 2008

Atlantic Ocean and measures of Atlantic hurricane activity have been reported to be strongly correlated since at least 1950 (refs 1-5), raising concerns that future greenhouse-gas-induced warming 6 could lead to pronounced increases in hurricane activity. Models that explicitly simulate hurricanes are needed to study the influence of warming ocean temperatures on Atlantic hurricane activity, complementing empirical approaches. Our regional climate model of the Atlantic basin reproduces the observed rise in hurricane counts between 1980 and 2006, along with much of the interannual variability, when forced with observed sea surface temperatures and atmospheric conditions 7 . Here we assess, in our model system 7 , the changes in large-scale climate that are projected to occur by the end of the twenty-first century by an ensemble of global climate models 8 , and find that Atlantic hurricane and tropical storm frequencies are reduced. At the same time, near-storm rainfall rates increase substantially. Our results do not support the notion of large increasing trends in either tropical storm or hurricane frequency driven by increases in atmospheric greenhouse-gas concentrations.