An assessment of representing land-ocean heterogeneity via convective
adjustment timescale in the Community Atmospheric Model 6 (CAM6)
Abstract
The time needed by deep convection to bring the atmosphere back to
equilibrium is called convective adjustment timescale or simply
adjustment timescale, typically denoted by 𝜏. In
the Community Atmospheric Model (CAM), convective adjustment timescale
is a tunable parameter with one value, 1 hour, worldwide. Albeit, there
is no justified reason why one adjustment timescale value should work
over land and ocean both. Continental and oceanic convection are
different in terms of the vigor of updrafts and hence can have different
longevities. So it is logical to investigate the prescription of two
different convective adjustment timescales for land
(𝜏𝐿) and ocean (𝜏𝑂) . To
understand the impact of representing land-ocean heterogeneity via
𝜏, we investigate CAM climate simulations for two
different convective adjustment timescales for land and ocean in
contrast to having one value globally.
Following a
comparative analysis of 5-year-long climate simulations, we find
𝜏𝑂 = 4 hrs and 𝜏𝐿 = 1 hr
to yield the best results. Particularly, we find better MJO simulations.
Although these 𝜏 values were chosen empirically
and require further tunning, the conclusion of our finding remains the
same, which is the recommendation to use two different
𝜏 values for land and ocean.