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While a quantitative climate theory of tropical cyclone formation remains elusive, considerable progress has been made recently in our ability to simulate tropical cyclone climatologies and to understand the relationship [...]

Recent research has strengthened the understanding of the links between climate and tropical cyclones (TCs) on various timescales. Geological records of past climates have shown century-long variations in TC numbers. While no significant trends have been identified in the Atlantic since the late 19th century, significant observed trends in TC numbers and intensities have occurred in this basin over the past few decades, and trends in other basins are increasingly being identified. However, understanding of the causes of these trends is incomplete, and confidence in these trends continues to be hampered by a lack of consistent observations in some basins. A theoretical basis for maximum TC intensity appears now to be well established, but a climate theory of TC formation remains elusive. Climate models mostly continue to predict future decreases in global TC numbers, projected increases in the intensities of the strongest storms and increased rainfall rates. Sea level rise will likely contribute toward increased storm surge risk. Against the background of global climate change and sea level rise, it is important to carry out quantitative assessments on the potential risk of TC-induced storm surge and flooding to densely populated cities and river deltas. Several climate models are now able to generate a good distribution of both TC numbers and intensities in the current climate. Inconsistent TC projection results emerge from modeling studies due to different downscaling methodologies and warming scenarios, inconsistencies in projected changes of large-scale conditions, and differences in model physics and tracking algorithms. WIREs Clim Change 2016, 7:65-89. doi: 10.1002/wcc.371 For further resources related to this article, please visit the . [ABSTRACT FROM AUTHOR]

Idealized tropical cyclones are inserted into a regional climate model and the resulting intensity evolution of the storms is examined under current and enhanced greenhouse climates. The regional climate model is imple-mented over a model domain near Australia. In general, storm intensities increase under enhanced greenhouse conditions, although these increases are mostly not statistically significant. The simulated intensities are compared to theoretically derived estimates of maximum potential intensity. The theoretical estimates are mostly larger than the simulated intensities, suggesting that other factors may be limiting the intensification of the storms. Two such factors are suggested: the limited horizontal resolution of the storm simulations and the presence of vertical wind shear. Significant regression relations are demonstrated between maximum intensity of the simulated storms as predicted by sea surface temperature and vertical wind shear variations, while much weaker relationships are shown between maximum intensity and sea surface temperature alone. This suggests that dynamical influences such as vertical wind shear, which are not included in theoretical estimates of maximum potential intensity, act to restrict the development of the storm and thereby its maximum intensity. [ABSTRACT FROM AUTHOR]

A regional climate model (DARLAM) is implemented over the Australian region and a 20-yr seasonally varying simulation is examined for the presence of tropical cyclone-like vortices (TCLVs). The horizontal resolution of the model is 125 km with nine vertical levels and is forced at its boundaries by the output of the Commonwealth Scientific and Industrial Research Organisation GCM using a mixed layer (or 'slab') ocean. Additional simulations are performed with a horizontal resolution of 30 km and with 18 vertical levels to examine the impact of increasing resolution on storm intensity. A sample of TCLVs from the 125-km resolution simulation is simulated at 30-km resolution to determine whether they reach observed tropical storm intensity at the finer resolution. It is found that stronger vortices in the 125-km resolution simulation are more likely to intensify when simulated at finer resolution than weaker vortices. In this way, a detection threshold for vortices generated in the 125-km resolution simulation is established and then used to detect TCLVs in that simulation. The regional climate model DARLAM provides a good simulation of both cyclogenesis and its seasonal variation under the current climate. The response of the model under enhanced greenhouse conditions is studied. Under 2 X CO[sub2] conditions, there is no statistically significant change in regions of formation of TCLVs, with only a slight southward shift simulated. Nevertheless, there are statistically significant effects on the poleward movement of TCLVs, with storms generally tending to travel farther poleward in a warmer climate once they have formed. An analysis is undertaken to determine the reasons for this behavior. While the dynamical constraints on the maintenance of TCLV intensity under 2 X CO[sub2] conditions (e.g., vertical wind shear) are similar to those in the current climate, thermodynamic conditions (e.g., sea surface temperatures) are quite different and are likely to... [ABSTRACT FROM AUTHOR]