Tropical oceanic mesoscale cold pools in observations and models
Convectively-generated cold pools over oceans contribute to important air-sea exchange of heat and moisture. Beyond cold pools’ physical properties, cold pools are important mechanisms controlling the life cycle of tropical convective systems. However, few observational techniques are available to routinely observe the properties of cold pools and their association with convection and convective storm environments. A new cold pool identification algorithm has been devised by applying computational topology on spaceborne scatterometer winds retrieved from EUMETSAT’s Advanced Scatterometer (ASCAT) and NASA’s RapidScat, two scatterometers that have provided ocean vector winds. Horizontal wind gradient is used as a proxy to identify cold pool envelopes termed as gradient features (GFs). Validation is carried out against a high-resolution model simulation and in situ oceanic buoy measurements. RapidScat, being in a non-sun-synchronous orbit, is able to resolve diurnal cycle of GFs and their properties. A first-ever global climatology of cold pool frequency, size and attributed TRMM 3B42 precipitation is created which helped us understand the tropical oceanic cold pool properties and their relationship with parent convection and rainfall. In addition, a bimodal frequency distribution is identified in cold pool properties from RapidScat and buoys. A conceptual model explaining the cold pool diurnal properties is created by relating GF properties and their environments.
To help relate the properties of cold pools, their parent convection, and the storm environment in a consistent framework, output from a 41-day simulation from the global Icosahedral Nonhydrostatic (ICON) model at 2.5 km grid spacing cloud-resolving model (CRM) output is compared with satellite-derived GF properties, as well as to leverage the simulation as a high-resolution analysis of the relationship between cold pool properties, their parent convective storms, and their environments, namely relationships between vertical wind shear, CAPE, humidity, and GF intensity and size. Principal component analysis (PCA) was applied on ICON model output and then K-means clustering was implemented to identify distinct clusters explaining differences in GF and environmental properties. Spatial linear regression helped us analyze regional differences between cold pool and environmental properties. In addition, statistical differences between the clusters helped us understand how the governing cold pool-MCS dynamics differs across the global tropical oceanic basins.
In this way, a comprehensive analysis of mesoscale cold pools, their parent convective systems and environmental properties was created in order to improve our understanding of mesoscale convective dynamics.
