AMIP II Diagnostic Subproject 31

Thermodynamic estimates of tropical cyclone intensity have provided a good tool for both understanding and predicting the factors that affect the intensification of tropical cyclones. These estimates employ the available energy existing in the atmosphere, together with that which becomes available from air-sea interactions, to provide an objective estimate of the maximum intensity that can be achieved. Published approaches either view tropical cyclones as a heat engine (Emanuel 1986, 1991, 1995) or treat themas a balance between moist adiabatic heating and buoyancy forcing (Holland, 1997).  Using observed monthly SST and real-time radiosonde sounding data near the tropicalcyclones location, Tonkin et al. (1998) evaluated both Emanuel and Holland's Maximum Potential Intensity (MPI) models against observed maximum intensity for a large number
of tropical cyclones. Results suggest that the thermodynamic model provides a good estimation (+- 20 hPa) of maximum intensity achieved by tropical cyclones. More recent work by the authors, as yet unpublished, has found that several dynamical factors contribute substantially to limiting the potential for tropical cyclones to reach the thermodynamic limit.

The approach developed by Holland (1997) was used by Henderson-Sellers et al. (1997) for estimating the potential changes of cyclone intensity associated with anthropogenic climate change. The results were subsequently confirmed in an independent modelling study by Knutson et al. (1998).

Therefore, the thermodynamic model provides an objective method of evaluating the climatology of the MPI and any changes of MPI that might be caused by climate change.  AMIP II experiments provide good opportunity to both extend the work of Henderson-Sellers et al. (1997) and to evaluate additional parameters that may inhibit intensification.

Objectives

The main objectives of this subproject are:

• To estimate the global MPI over ocean, including the evaluation of the climatology of MPI for current climate using both climate model output and the NCEP reanalysis.
• To update and extend the work of Henderson-Sellers et al (1997) by application of the approach of Holland (1997) to climate change scenarios, and to examine the impact of several dynamical processes.

The thermodynamical approach of Holland (1997) will be applied to AMIP II simulation
outputs to estimate MPI. In addition, we shall apply the recent work of Holland, Wang
and Qu on the limitations on intensification induced by dynamical processes.

The estimated MPI will be compared with the MPI calculated using the NCEP reanalysis
data set in order to assess the ability of the AMIP II models to simulate the MPI.

The observed Tropical Cyclone Best Track data for different basins will be used to
validate the estimated MPI.

Data Requirements

Low frequency (monthly mean) data will be used.  We will require the following model
output fields, structured by tables as in the AMIP II Standard Model Output list:

Table 1a: Upper-air monthly mean: Basic

• Air temperature
• Northward wind
• Eastward wind
• Specific humidity
• Relative humidity

• Ground temperature (Sea surface temperature if available)
• Surface pressure

Emanuel, K.A., 1986: An air-sea interaction theory for tropical cyclones. Part1: Steady-state maintenance. J. Atmos. Sci., 43, 585-604.

Emanuel, K.A., 1991: The theory of hurricanes, Annu. Rev. Fluid. Mech., 23, 179-196.

Emanuel, K.A., 1995: Sensitivity of tropical cyclones to surface exchange coefficients and a revised stead-state model incorporating eye danamics. J. Atmos. Sci., 52, 3969-3976.

Henderson-Sellers A., G. Berz, K. Emanuel, W.M. Gray, C. Landsea, G. Holland, J. Lighthill, S-L. Shieh and H. Zhang, 1997: Tropical Cyclones and Global Climate Change. Bull. Amer. Meteor. Soc., 79, 9-38.
 

Holland, G. J., 1997: The maximum Potential Intensity of Tropical Cyclones., J. Atmos. Sci., 54, 2519-2541.

Knutson, T.R., R.E. Tuleya, and Y. Kurihara, 1998: Simulated increase of hurricane intensities in a CO2-warmed climate. Science, 279, 1018-1020.

Tonkin, H, G.J. Holland, N. Holbrook, and A. Henderson-Sellers, 1998: An evaluation of thermodynamic estimations of climatological maximum potential tropical cyclone intensity. Mon. Wea. Rev. (in press).
 

LLNL Disclaimers

UCRL-MI-127350