To better understand the global energy balance and climate, profiling the subtropical cloud-topped marine boundary layer is crucial, as recent observations reveal the significant impact of low-level subtropical stratoform clouds on the radiation budget. For this purpose we use a theoretical framework - mixed layer theory, a simple but profound concept, to evaluate the representation, and state of the subtropical marine boundary layer. The present climate models to simulate cloudiness are still complicated for realistic analysis as parametrizing the radiative cooling and entrainment processes involved is an issue , we use this model to answer the following questions, atleast in a qualitative sense.
(a) What is the seasonal distribution of the low-stratiform clouds in different regions of the globe, ? and what are the appropriate cloud characteristics to determine this distribution ? In a stratocumulus topped boundary layer regime by prescribing the state of free-troposphere, structure of the mixed layer and the large-scale forcing, the mixed layer framework is used to determine the thermodynamic state of the system, namely the liquid-water static energy ($s_l = c_p T + g z - L q_l$) and the total-water specific humidity ($q_t$), and the boundary layer height ($h$) (details in the section (2)). For the analysis we group the oceans into 8 regions - North and South Pacific, North and South Atlantic, North and South Indian, and finally Arctic and Antarctic. For each region we determine the seasonal variation of the cloud characteristics - the cloud-top height, cloud-base height and spatial distribution of the cloud within that region in terms of sea surface temperature (SST), divergence and the large-scale forcing : Radiative forcing across the interface ($\Delta F$) and static energy forcing across the interface ($\Delta s$).
(b) What is the relative extent of importance of the various processes and if we can determine a single parameter based on the large scale input forcing fields to profile the solutions of the mixed layer ? A nondimensional parameter which evoloves naturally from the mixed-layer solutions (see section(2)) is $\sigma$ ($\sigma = \frac{V \Delta S}{\Delta F}$). We analyse the boundary layer solutions in terms of $\sigma$.
(c) Perform statistical tests which permit a straight forward assessment of the extent to which the various models agree or differ with respect to a prescribed set of metrics. These metrics can also be used as a powerful diagnostic tool for model validation. These metrics which give a qualitative comparisons between different models are (1) Number of solutions in each region (2) location of center of mass of the solution within each region, which gives an indication of the distribution of the solution. (3) averaged cloud-base height (4) averaged cloud-top or boundary layer height.
Presentation: Stratocumulus and Mixed layer theory