1. Hurricane Frequency and Sea Surface Temperature EAS 4803 Sheliza Bhanjee

2. Background Hurricane formation is dependent on Hurricane formation is dependent on Sea surface temperatureSea surface temperature Vertical wind shearVertical wind shear Sea level pressureSea level pressure Latent heat fluxLatent heat flux Hurricanes can form when sea surface temperatures reach 26.5°C Hurricanes can form when sea surface temperatures reach 26.5°C

3. Over the past 100 years, increase in SST (~0.3°C) Over the past 100 years, increase in SST (~0.3°C) Also increase in hurricane frequency and intensity Also increase in hurricane frequency and intensity Category 4 and 5 hurricanes in the past 35 years have doubled Category 4 and 5 hurricanes in the past 35 years have doubled However, technology has also improved However, technology has also improved Better data collection methods Better data collection methods Curry et al., 2005

4. Data Monthly average Tropical N Atlantic SST data Monthly average Tropical N Atlantic SST data Number of hurricanes per month (frequency) Number of hurricanes per month (frequency) 1948-2004 1948-2004 Obtained from NOAA Obtained from NOAA Climate Indices: Monthly Atmospheric and Ocean Time SeriesClimate Indices: Monthly Atmospheric and Ocean Time Series Regression and time series analysis Regression and time series analysis

5. Data

6. Correlation and Regression Analysis Low correlation, noisy data

7. Periodograms Seasonal variation with hurricane frequency Highly variable temperature across years, but steady increase (1970s)

8. Cross Spectral Analysis As years increase, relationship strengthens Large dip in correlation around 1953

9. Coherence Low correlation Variable at first, then stabilizes

10. Conclusions No strong, direct relationship shown across all statistical techniques No strong, direct relationship shown across all statistical techniques Although sea surface temperatures may not directly affect hurricane frequency, might have indirect effect Although sea surface temperatures may not directly affect hurricane frequency, might have indirect effect Short data time period- maybe long term SST /frequency relationship is better Short data time period- maybe long term SST /frequency relationship is better Measuring techniques not uniform until recently Measuring techniques not uniform until recently