Gulf Stream and ENSO Increase the Temperature Sensitivity of Atlantic Tropical Cyclones

Abstract

Controversy exists over the role of the recent rise in sea surface temperatures (SST) and the frequency of tropical cyclones or hurricanes. Here, 135 yr of observational records are used to demonstrate how sea surface temperature, sea level pressure, and cyclone numbers are linked. A novel wavelet-lag coherence method is used to study cause and effect relations over a large space of time scales, phase lags, and periods. It is found that SST and cyclones are not merely correlated, but are in a negative feedback loop, where rising SST causes increased numbers of cyclones, which reduce SST. This is statistically most significant at decadal and not at longer periods, which is contrary to expectations if long-period natural cycles are important in driving cyclone numbers. Spatial relationships are examined using phase-aware teleconnections, which at the dominant decadal period show the in-phase behavior of the Atlantic SST in the Gulf Stream region, reflecting the role of the transportion of heat northward from the tropical Atlantic. At 5-yr periods there is significant coherence when SST leads cyclones by 2 yr, and this is associated with tropical ENSO activity such that, as predicted, increasing numbers of El Niños cause fewer Atlantic cyclones. The pattern of coherence existing since 1970 strongly favors the decadal coherence band, and despite growing coherence at higher frequencies, there is none at the 5-yr band, perhaps explaining why the observed sensitivity between SST and cyclones is larger than that from general circulation model (GCM) predictions and becoming greater.

Projected Atlantic hurricane surge threat from rising temperatures

“…Fig. 2A indicates the importance of land temperatures rather than SSTs, although the weak North Atlantic feature is consistent with earlier suggested links (2,35,37). One possible explanation could be a better observational network and thus a higher signalto-noise ratio of land temperatures.…”

“…The weaker positive relationship between the SSTs over the Atlantic subpolar gyre and k, has been mechanistically related to reduced wind shear and increased precipitation in the MDR (34). A warm subpolar gyre produces a reduced temperature gradient with the equator, a reduced northward heat transport (34), and an anomalously warm SST in the MDR (35).…”

Atlantic hurricane surge response to geoengineering

“…1); that is, most regional temperatures are much worse predictors of hurricanes than global mean temperatures. This behavior is consistent with several known teleconnection patterns (5,6,18) related to Atlantic hurricanes.…”

“…The southward shift of the ITCZ would likely also affect runoff in Amazonia, altering ocean mixing of cold water to the surface in the tropical Atlantic, as described previously. Stratospheric aerosol geoengineering results in a longer westerly phase of the Quasi-Biennial Oscillation (QBO) (27), and with Return levels at 2070 were estimated taking into account local land subsidence, plus the 50th percentile rises forecast at the tide gauge sites for 2070 estimated under RCP4.5 (18) or G4 (4). The differences between global (MDR) warm and cold year mean temperatures over the historical period are 0.42°C (0.37°C) from observations (38) and 0.37°C (0.31°C) from the models used here (legend for Fig.…”

Homogeneous record of Atlantic hurricane surge threat since 1923

“…Some have linked cyclone activity to sea surface temperatures in the cyclogenesis region (2,4). Other competing hypotheses include teleconnections with El Niño-Southern Oscillation (5), North Atlantic Oscillation (6)(7)(8), Atlantic Multidecadal Oscillation (6), tropical temperatures (3,9), and Sahel drought (10). Whereas others note that bias in the observational record casts doubt on any statistical power from the relationship (11).…”