Tropical Cyclone Simulations in CAM5: The Impact of the Dynamical Core Kevin A. Reed National Center for Atmospheric Research Julio Bacmeister, Cecile Hannay, Peter Lauritzen & John Truesdale NCAR Michael Wehner & Prabhat LBNL June 18th, 2014 1
Background Outline CAM5 has shown some skill in simulating extreme weather events, especially at higher horizontal resolutions (~ 25 km). This is particularly true for the simulation of Tropical Cyclones (TCs). However, there is still much room for improvement as there exist biases in intensity, track duration, regions of formation, etc. In addition, there is uncertainty in the impact of tuning the model on extremes at these high horizontal resolutions. June 18th, 2014 2
CAM5-FV 0.9 o by 1.25 o Outline Storm Tracks - AMIP June 18th, 2014 [Wehner et al. 2014, JAMES] 3
CAM5-FV 0.23 o by 0.31 o Outline Storm Tracks - AMIP June 18th, 2014 [Wehner et al. 2014, JAMES] 4
Outline Observations June 18th, 2014 5
Motivation Outline There is certainly a lot of room for improvement. It is expected that some of these biases, particularly in TC genesis and tracks, can be improved by continued improvement in large-scale circulations and climate. Model design choices are an important source of uncertainty for the simulation of TCs. This is widely documented for physical parameterization suites, but it is less recognized for the dynamical component of models and the physics-dynamics coupling. June 18th, 2014 6
Outline Impact of Dynamical Core Past work has investigated the impact of the dynamical core on idealized tropical cyclones in CAM5. Wind Speed (m/s) At Day 10 Differing strengths and shapes: FV & SE at 0.25 o ( 28 km) EUL & SLD at T340 ( 39 km) Category-4 June 18th, 2014 [Reed & Jablonowski 2012, JAMES] cyclone 7
Design Outline of Experiments NCAR Community Atmosphere Model version 5. The default Spectral Element SE dynamical core with 30 vertical levels is used at the horizontal resolution of ne120 (~25 km) comparable to previous CAM5-FV 0.23 o x0.31 o run. The main difference between the two runs is the dynamical core (FV vs. SE). Full CAM5 physics with Atmospheric Model Intercomparison Project (AMIP) protocols for 1980-2005. Prescribed observed SSTs, ozone, CO 2, solar forcing, etc. A new GFDL tracking code is being tested and used for calculating all tracks (still in development). June 18th, 2014 8
Outline TC Track Density CAM5-SE IBTrACS CAM5-FV [Reed et al. 2014, in prep.] June 18th, 2014 9
Global Counts Outline Comparison Observations CAM5-FV CAM5-SE Tropical Storms 91.2±8.3 84.2±10.9 84.1±11.4 Hurricane 47.9±5.5 57.1±8.4 69.8±10. Major Hurricane (cat. 4 &5) 10.7±3.3 8.3±3.0 21.8±5.0 June 18th, 2014 10
Outline Global Statistics June 18th, 2014 [Reed et al. 2014, in prep.] 11
Outline North Atlantic Basin June 18th, 2014 12
Outline TC Climatology June 18th, 2014 [Reed et al. 2014, in prep.] 13
Outline TC Intensity Distributions June 18th, 2014 14
Why? Outline June 18th, 2014 15
Final Thoughts Outline The impact of the dynamical core on tropical cyclone statistics for the decadal experiments is significant. Needs to continue to be explored! The high-resolution CAM5-SE produces more hurricanes per year than observed from 1980-2005 and more than that seen in the previous CAM5-FV AMIP simulation. Additional work needs to be performed to understand these difference, particularly the link between the dynamics and the physics. Furthermore, understanding why CAM5-SE produces stronger storms than CAM5-FV, even when the theoretical intensity is higher in CAM5- FV. We are developing a intermediate test bed to provide insight into the simulation of tropical climate at high-resolutions, as well as the model s ability to simulate extreme events such as tropical cyclones. June 18th, 2014 16
Intermediate Outline Test Bed: Uniformly rotating RCE World 6-hr Avg. Precipitation (mm/day) CAM5-SE ne30 (~100 km) CAM5-SE ne120 (~25 km) June 18th, 2014 [Corilois set to 10 deg. N] 17
Intermediate Test Bed: Outline Uniformly rotating RCE World ne30: Avg. Count = 10.9 Avg. Max. Wind = 34.7 m/s Avg. Min. PS = 967 hpa ne120: Avg. Count = 13.6 Avg. Max. Wind = 40.9 m/s Avg. Min. PS = 961. hpa June 18th, 2014 18
Intermediate Outline Test Bed: TC Size and Structure CAM5-SE ne30 (~100km) 5 year simulation June 18th, 2014 19
Thanks! Outline CAM5-FV June 18th, 2014 20