ABSTRACT

The main focus of the research is to study the impact of rapidly varying (on daily and sub-daily timescales) sea surface heat fluxes on atmosphere-ocean coupling. Literature indicates that the clear separation between the dynamical timescales of the ocean and atmosphere allows a simple paradigm for much air-sea interaction in which the rapidly varying component of surface heat fluxes is approximated by a stochastic term. However, this heat flux term depends upon not only the "fast" atmosphere but also upon the "slow" ocean. Thus, the stochastic noise should not be independent of the oceanic state, contrary to most past studies. Notably, such state-dependent (multiplicative) noise can alter low-frequency ocean dynamics through a process known as noise-induced drift. Accurate representation of this drift is necessary but difficult in climate models, since noise-induced drift cannot be simply parameterized by constant terms as its strength depends on the variance of the heat flux variability, a function of time and space. The aim of this project is to understand how the multiplicative noise character of the heat flux contributes to climate variability and predictability on interannual to inter-decadal timescales, and how it might contribute to biases found in many coupled models. Thus, it is imperative to study the effect of state-dependent rapidly varying heat fluxes (including heat advection through ocean currents, surface heat fluxes, entrainment, and horizontal mixing) using observations and coupled model runs. Since deviations from Gaussianity, or anomalous statistics, can shed light on the underlying state-dependent character of the heat fluxes, one of the main objective of the research is to globally map the non-Gaussianity (e.g., higher moments: skewness, kurtosis) of oceanic and atmospheric quantities relevant for atmosphere-ocean coupling from a broad range of observational datasets and a hierarchy of coupled model runs. Experiments with coupled models will also be used to understand how details of numerical coupling impact model representation of this process.

Intellectual Merit: A meticulous study of fast-varying heat fluxes and its impact on air-sea interaction is important because the fast-varying variability of heat fluxes must be accurately simulated to correctly model sea surface temperature (SST) and air temperature (TAIR) variability, and the coupling scheme must be appropriate to capture heat flux variability on daily and sub-daily time scales. The PI will (1) extend a systematic stochastic framework that has been developed over the last decade to understand the interaction of slowly and rapidly varying components of the climate system, such as SST and TAIR anomalies, and (2) develop improved coupling schemes and the implementation of stochastic parameterizations in weather and climate models.

Broader Impacts: The research will further our understanding on how the ocean interacts with the atmosphere and vice versa and helps climate diagnostics and modeling communities. The results will be disseminated as maps of non-Gaussian statistics of various quantities on the NOAA-CIRES CDC web page.

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