(2007) specifically found that model projections with increased resolution predicted a larger increase in the frequency of intense TCs in future climates, highlighting the need for high-resolution models, with explicit convection, in studies of future TC intensity change. 2007) however, still higher resolution is required to reproduce observed TC intensities. Recently, GCM projections with grid spacings of less than 30 km have provided evidence for increasing TC intensity in a warmed climate (e.g., Oouchi et al. ![]() Because of these limitations, tropical disturbances in these models are often referred to as being “TC like” in that the modeled storms are larger in size and weaker than those observed. For coarse GCM simulations, cumulus parameterization (CP) implicitly accounts for subgrid-scale precipitation, parameterizing a portion of the TCs secondary circulation, degrading its realism and impacting TC intensity as well (e.g., Davis and Bosart 2002). Because of the large computational expense associated with long-term integrations, GCMs are required to use horizontal resolution that is unable to realistically simulate important storm-scale physical processes that determine TC intensity (e.g., storm-scale variations in turbulent fluxes, secondary circulation, and eye–eyewall processes), in part stemming from the need to parameterize subgrid-scale convection. Projections of future global climate change are often made with the aid of coupled atmosphere–ocean general circulation models (GCMs). ![]() Since this original inquiry, a large number of additional studies have pursued this topic, utilizing a variety of approaches. This possibility was raised by Emanuel (1987), who used a theoretical model of TC intensity to propose that TCs in a greenhouse gas–warmed climate would have higher potential intensities than in the present-day climate. This relationship between TC intensity and SST suggests that a future increase in SST could potentially support increased intensity of TCs, provided that other climate processes do not offset this effect. In the absence of external factors detrimental to tropical cyclone (TC) intensification (e.g., vertical wind shear, dry air entrainment, oceanic upwelling, land interactions, etc.) the maximum intensity of a TC generally increases as the sea surface temperature (SST) increases (e.g., DeMaria and Kaplan 1994 Emanuel 1986, 1988, 1995 Holland 1997). Enhanced upper-tropospheric warming in the GCM environment is shown to be an important mitigating influence on TC intensity change but is also shown to exhibit large uncertainty in GCM projections. The increase in precipitation is consistent with a stronger potential vorticity tower, a warmer eye, and lower central pressure. ![]() Inner-core precipitation increases of 10%–30% are found for future simulations, with large sensitivity to the emission scenario. The depth of the TC secondary circulation increases in future simulations, consistent with an increase in the height of the freezing level and tropopause. For the 2-km simulations, the average increase was 14% (~14 hPa). Future TC intensity increased for 75 of 78 future simulations using 6-km grid length, with a 9% (~8 hPa) average increase in central surface-pressure deficit. Some processes known to impact TC intensity, such as environmental vertical wind shear and sea surface wake cooling, are not considered in this study. These changes are then added to the reanalysis-derived initial and boundary conditions used in the control simulations. Changes between the periods 1990––99 are computed using output from 13 GCMs from the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4), for the A1B, A2, and B1 emissions scenarios. The analyzed tropical environment is used for control simulations. ![]() With the goal of isolating the influence of thermodynamic aspects of climate change on maximum hurricane intensity, an idealized TC is placed within a quiescent, horizontally uniform tropical environment computed from averaged reanalysis data for the tropical Atlantic Ocean. A comprehensive analysis of tropical cyclone (TC) intensity change in a warming climate is undertaken with high-resolution (6- and 2-km grid spacing) idealized simulations using the Weather Research and Forecasting (WRF) model.
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