DOI: 10.25921/ejb6-5455
title: NOAA/WDS Paleoclimatology - Early Pliocene Tropical Cyclone SST Modeling Results

description: Tropical cyclones (also known as hurricanes and typhoons) are now believed to be an important component of the Earth's climate system. In particular, by vigorously mixing the upper ocean, they can affect the ocean's heat uptake, poleward heat transport, and hence global temperatures. Changes in the distribution and frequency of tropical cyclones could therefore become an important element of the climate response to global warming. A potential analogue to modern greenhouse conditions, the climate of the early Pliocene epoch (approximately 5 to 3 million years ago) can provide important clues to this response. Here we describe a positive feedback between hurricanes and the upper-ocean circulation in the tropical Pacific Ocean that may have been essential for maintaining warm, El Nino-like conditions during the early Pliocene. This feedback is based on the ability of hurricanes to warm water parcels that travel towards the Equator at shallow depths and then resurface in the eastern equatorial Pacific as part of the ocean's wind-driven circulation. In the present climate, very few hurricane tracks intersect the parcel trajectories; consequently, there is little heat exchange between waters at such depths and the surface. More frequent and/or stronger hurricanes in the central Pacific imply greater heating of the parcels, warmer temperatures in the eastern equatorial Pacific, warmer tropics and, in turn, even more hurricanes. Using a downscaling hurricane model, we show dramatic shifts in the tropical cyclone distribution for the early Pliocene that favour this feedback. Further calculations with a coupled climate model support our conclusions. The proposed feedback should be relevant to past equable climates and potentially to contemporary climate change.
description: This data set contains long-term average sea surface temperatures from the three different simulations included in figure 4 of Fedorov et al. 2010 

Model results are presented in 3 netCDF files - Fedorovetal2010_co2_only.avg176-200.SST.nc, Fedorovetal2010_mixing_bands_and_co2.avg_176-200.SST.nc, Fedorovetal2010_preindustrial.SST.nc

We reconstruct hurricane characteristics by completing several successive steps, including (1) reconstructing the SST field; (2) modelling the large-scale atmospheric circulation with a general circulation model (GCM); and (3) using the GCM data to drive a statistical downscaling model (SDSM), which computes synthetic hurricane tracks and intensity 

Latitudes of gridpoints included as variable TLAT in files (note data on gx1v3 rotated ocean grid)
Longitudes of gridpoints included as variable TLONG in files (note data on gx1v3 rotated ocean grid)  
 
The simulations were performed with CCSM3 at T42_gx1v3 resolution in fully coupled mode. The preindustrial simulation is a continuation of NCARs preindustrial run. The increasing CO2 simulation raises the CO2 level from 280 to 355ppm instantaneously at the beginning of the simulation and is taken from the final 25 yrs of a 200 year long simulation. The hurricane mixing and CO2  run includes 355ppm of carbon dioxide as well as and additional 1cm2/s increase in the background vertical diffusivity between 8-40 degrees in both hemispheres 
 
Data generated in 2008 and 2009 by Chris Brierley on Yale's BulldogJ supercomputer