Tropical Cyclones in the 7km NASA Global Nature Run for use in Observing System Simulation Experiments.

Area of Science:

• Atmospheric Science
• Climate Modeling
• Tropical Meteorology

Background:

• The NASA Nature Run (NR) is a global, high-resolution simulation designed for Observing System Simulation Experiments (OSSEs).
• Evaluating the NR's capability to realistically represent tropical cyclone (TC) activity is crucial for its utility in OSSEs.

Purpose of the Study:

• To assess the fidelity of the NASA Nature Run (NR) in simulating tropical cyclone (TC) activity across all major ocean basins.
• To determine if the NR provides realistic large-scale forcings necessary for generating TCs.

Main Methods:

• The NR, a 2-year global non-hydrostatic simulation at 7 km resolution, was analyzed for TC activity.
• The simulation incorporated observed sea-surface temperatures (SSTs), sea ice, and interactive aerosols/trace gases.
• Dynamical features, African Easterly Waves, and TC characteristics (tracks, life spans, structures) were examined.

Main Results:

• The NR accurately reproduced realistic dynamical features in the African Monsoon and tropical Atlantic, including African Easterly Waves.
• Atlantic TC seasons in the NR exhibited interannual variability consistent with observations, with stronger activity in 2005.
• The NR successfully captured fundamental aspects of TC seasons in all basins, including realistic TC numbers, tracks, life spans, and structures.

Conclusions:

• The NASA Nature Run (NR) demonstrates suitability as a tool for OSSEs focused on tropical cyclones (TCs).
• The NR represents an advancement over previous long-term simulations for the atmospheric OSSE community, particularly for TC research.