Takahashi et al. (2025) Land‐Ocean Differences in Tropical Deep Convective Clouds: Intercomparison of DYAMOND Simulations and CloudSat Observations

Identification

• Journal: Journal of Geophysical Research Atmospheres
• Year: 2025
• Date: 2025-12-04
• Authors: Hanii Takahashi, Longtao Wu, Mark A. Smalley, Graeme Stephens, Kentaroh Suzuki, Derek J. Posselt
• DOI: 10.1029/2025jd044688

Research Groups

• Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
• Joint Institute for Regional Earth System Science and Engineering, University of California, Los Angeles, CA, USA
• Department of Meteorology, University of Reading, Reading, UK
• Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan
• National Oceanic and Atmospheric Administration (NOAA), USA (X-SHiELD model)
• NASA's Goddard Space Flight Center (NASA/GSFC), USA (GEOS model)
• European Centre for Medium-Range Weather Forecasts (ECMWF), UK (IFS model)
• Centre of Excellence in Simulation of Weather and Climate in Europe (CESiWACE)
• German Climate Computing Center (DKRZ)

Short Summary

This study compares tropical deep convective clouds and their environments in DYAMOND simulations with CloudSat observations across three tropical regions. It finds that while DYAMOND models capture environmental differences, they exhibit biases in representing convective intensity and precipitation dynamics, particularly overestimating convection in the Tropical Warm Pool.

Objective

• To investigate how deep convective clouds and their environments are represented in DYAMOND simulations compared to CloudSat observations, focusing on land-ocean contrasts across three tropical "chimney zones" and identifying model biases in convective intensity and precipitation dynamics.

Study Configuration

• Spatial Scale: Three tropical "chimney zones": Tropical Africa (5°–40°E, 15°S–15°N), Tropical Amazonia (80°–35°W, 25°S–5°N), and the Tropical Warm Pool (90°–180°E, 15°S–15°N). CloudSat observations have horizontal resolutions of 1.7 km along track and 1.3 km across track, with a vertical resolution of 480 m (oversampled to 240 m). DYAMOND models include X-SHiELD (3.0 km), GEOS (1.5 km and 3.0 km), and IFS (4.0 km). ECMWF-AUX data has a 50 km resolution.
• Temporal Scale: CloudSat observations from 30 January to 28 February 2007. DYAMOND simulations from 30 January to 28 February 2020 (DYAMOND Winter). All data are sampled at 1:30 a.m./p.m. local time.

Methodology and Data

• Models used:
  • DYAMOND Winter simulations: X-SHiELD 3.0 km, GEOS 1.5 km, GEOS 3.0 km, IFS 4.0 km.
  • Passive-Active Microwave Simulator (PAMS), an extension of Quickbeam simulator, for generating radar reflectivity from model outputs.
• Data sources:
  • Satellite observations: CloudSat (94 GHz Cloud Profiling Radar - CPR) products 2B-GEOPROF (radar reflectivity, cloud mask) and ECMWF-AUX (vertical temperature and moisture profiles).
  • Reanalysis: European Centre for Medium-Range Weather Forecast (ECMWF) operational forecast (for ECMWF-AUX data).
  • DYAMOND data server (for model outputs).

Main Results

• DYAMOND simulations generally capture environmental differences (e.g., virtual temperature profiles, Level of Free Convection, Level of Neutral Buoyancy, Convective Available Potential Energy) among the three tropical regions, with the exception of the SHiELD-3km simulation.
• CloudSat observations indicate that convective intensity is strongest over Tropical Africa, followed by Tropical Amazonia, and weakest over the Tropical Warm Pool (TWP), characterized by higher echo top heights (ETH0dBZ, ETH10dBZ) and shorter cloud top-echo top distances (CTETD0dBZ, CTETD10dBZ) over land. Cloud top height (CTH) is relatively uniform across regions in CloudSat data.
• In contrast to observations, DYAMOND simulations tend to produce the deepest and most intense convection over the TWP, followed by Tropical Amazonia, and then Tropical Africa. This pattern is particularly evident in the GEOS-1km and GEOS-3km simulations.
• DYAMOND simulations tend to overestimate CTH, ETH0dBZ, and ETH10dBZ over the TWP and underestimate them over Tropical Africa.
• The Contoured Frequency by Temperature Diagrams (CFTDs) from DYAMOND simulations do not exhibit the "inverse-C" shape observed by CloudSat, suggesting that models produce significantly heavier precipitation at higher altitudes (colder temperatures) than observed.
• DYAMOND models show very low mean updraft speeds (typically 0.35 to 1.04 m/s), yet produce heavy precipitation at high altitudes, indicating a potential disconnect between cloud dynamics and microphysics, where precipitation may form rapidly in upper layers without strong vertical transport.
• The GEOS-1km (atmosphere-only) and GEOS-3km (coupled) simulations show no significant differences, suggesting that improvements in model physics can, to some extent, compensate for coarser resolution.

Contributions

• Provides the first comprehensive intercomparison of DYAMOND storm-resolving simulations with CloudSat observations to evaluate land-ocean differences in tropical deep convection.
• Identifies specific and systematic biases in DYAMOND simulations regarding convective intensity, precipitation dynamics, and the coupling of cloud dynamics and microphysics.
• Highlights that DYAMOND models misrepresent the conversion efficiency of Convective Available Potential Energy (CAPE) to kinetic energy, particularly over oceanic regions like the Tropical Warm Pool.
• Offers novel diagnostic tools (proxies for convective strength, CFTD) for a more direct and meaningful comparison between global storm-resolving models and satellite observations.
• Emphasizes the critical need for improved representation of cloud microphysics and updraft dynamics, as well as their interactions, in current global models.

Funding

• NASA Grants: 80NSSC20K0090, 80NM0018F058
• INCUS project: Grant 80LARC22DA011
• MEXT program for the Advanced Studies of Climate Change Projection (SENTAN): Grant JPMXD0722680395
• JAXA/EarthCARE project
• European Union's Horizon 2020 research and innovation programme (ESiWACE and ESiWACE2): Grant agreements No 675191, 823988
• Deutsches Klimarechenzentrum (DKRZ): Project IDs bk1040, bb1153

Citation

@article{Takahashi2025LandOcean,
  author = {Takahashi, Hanii and Wu, Longtao and Smalley, Mark A. and Stephens, Graeme and Suzuki, Kentaroh and Posselt, Derek J.},
  title = {Land‐Ocean Differences in Tropical Deep Convective Clouds: Intercomparison of DYAMOND Simulations and CloudSat Observations},
  journal = {Journal of Geophysical Research Atmospheres},
  year = {2025},
  doi = {10.1029/2025jd044688},
  url = {https://doi.org/10.1029/2025jd044688}
}