Sensitivity of tropical cyclone track forecasts to convective momentum transport in the NOGAPS Emanuel cumulus parameterization

Since the introduction of the Emanuel cumulus parameterization into the Navy Operational Global Atmospheric Prediction System (NOGAPS) in May 2002, NOGAPS medium range (greater than 72 hours) tropical cyclone track forecasts have demonstrated a significant improvement. One of the key components in the Emanuel parameterization is the transport of momentum by the cumulus updrafts and downdrafts. In data assimilation/medium range forecast tests for the period August 2004 – September 2004 we demonstrate the sensitivity of the tropical cyclone tracks to the amount of convective momentum transport in the original Emanuel scheme. It is shown that in NOGAPS the tropical cyclone track performance is seriously degraded if the convective momentum transport mechanism is turned off. Data assimilation/medium range forecast results are also presented over the same test period with an alternative algorithm for convective momentum transport developed by Robe and Emanuel (2001).