The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment – Part 1: The role of the easterly wave critical layer Naval Postgraduate School, Monterey, California, USA
Received: 05 Jun 2009 – Published in Atmos. Chem. Phys. Discuss.: 16 Sep 2009Abstract. An observational and real-time model forecast study of the genesis of
Typhoon Nuri during the Tropical Cyclone Structure 2008 (TCS-08) field
campaign in the western North Pacific sector is presented. Analysis and
observational data show that the surrounding base state is an easterly trade
wind flow and the precursor disturbance to Typhoon Nuri is an easterly wave
that originates in the ITCZ in the Central Pacific. This disturbance can be
tracked more than 10 days prior to tropical storm formation. An overview of
the field data is presented here using a newly proposed dynamical framework
for tropical cyclone formation within the critical layer of an easterly
wave. Despite propagating through a hostile environment ripe with strong
vertical wind shear and relatively dry air, the easterly wave critical layer
protects the proto-vortex and allows it to gestate until it reaches a more
favorable environment. Within this protective "Kelvin cat's eye flow"
located within the wave's critical layer existed a sweet spot, defined as
the intersection between the wave trough and critical latitude, which is the
preferred location for tropical cyclogenesis. Global Forecast System Final
Analyses and IR satellite imagery, which shows convective bands wrapping
around the sweet spot as genesis nears, confirm that this sweet spot is the
location where Typhoon Nuri's dominant low-level circulation emerges.
Revised: 14 Apr 2010 – Accepted: 25 May 2010 – Published: 20 Oct 2010
United States Air Force C130 and Naval Research Laboratory P3 research
flights on 16 and 17 August collected flight-level,
dropwindsonde, and Doppler radar data that allowed an evaluation of the
dynamic and thermodynamic processes within the cat's eye circulation. The
dropwindsonde analyses identifies the precursor easterly wave disturbance on
16 August and identifies an area of weak low-level cyclonic circulation on
Real-time forecasts were produced using operational global prediction model
data to support scientific missions during TCS-08. These forecasts were
found to be useful in flight planning discussions and predicted Typhoon
Nuri's eventual genesis latitude within 1.5 degrees 72 h in advance.
Citation: Montgomery, M. T., Lussier III, L. L., Moore, R. W., and Wang, Z.: The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment – Part 1: The role of the easterly wave critical layer, Atmos. Chem. Phys., 10, 9879-9900, doi:10.5194/acp-10-9879-2010, 2010.