The impact of current and possibly future sea surface temperature anomalies on the frequency of Atlantic hurricanes
Krishnamurti, T. N.
- Publisher: Co-Action Publishing
(issn: 1600-0870, eissn: 0280-6495)
A brief summary of the current capabilities of a high resolution global numerical predictionmodel towards resolving the life cycles of hurricanes is first presented. Next, we illustrate theresults of season long integrations for the years 1987 and 1988 using the observed sea surfacetemperature (SST) anomalies over the global oceans. The model being used here is the FSUatmospheric global spectral model at the horizontal resolution of T42 and with 16 verticallayers. The main emphasis of this study is on hurricane tracks for these and for global warmingexperiments. The global warming scenarios were modeled using doubled CO2 and enhancedSST anomalies. The model being atmospheric does not simulate the ocean, and SST anomaliesneed to be prescribed. It is assumed in these experiments that the SST anomalies of the doubled CO2 world appear similar to those of the current period but that they are slightly warmer overthe global tropics. That is determined using a simple proportionality relationship requiring anenhancement of the global mean SST anomaly over the tropics. Such an enhancement of theSST anomaly of an El Niño year 1987 amplifies the SST anomaly for the El Niño of the double CO2 atmosphere somewhat. The La Niña SST anomalies were similarly enhanced for the double CO2 atmosphere during 1988. These hurricane season experiments cover the period Junethrough October for the respective years. It was necessary to define the thresholds for a modelsimulated hurricane; given such a definition we have compared first the tracks and frequencyof storms based on the present day CO2 simulations with the observed storms for 1987 and1988. Those comparisons were noted to be very close to the observed numbers of the storms.The doubled CO2 storms show a significant enhancement of the frequency of storms for the La Niña periods, however there was no noticeable change for the El Niño experiments. Wehave also run an experiment using the SST anomalies from a triple CO2 climate run made atthe Max Planck Institut at Hamburg. This experiment simulated some 7 hurricanes over the Atlantic Ocean. The intensity of hurricanes, inferred from maximum winds at 850 mb, showthat on the average the storms are slightly more intense for the double CO2 experimentscompared to the storms simulated from current CO2 conditions. The triple CO2 storms wereslightly stronger in this entire series of experiments.DOI: 10.1034/j.1600-0870.1998.t01-1-00003.x