RDC as Unforced But Strongly-Bound Circulation

First uploaded on 2022/08/21
Last updated on 2023/02/13
Copyright(C)2022 jos <jos@kaleidoscheme.com> All rights reserved.

Many of the flows treated in meteorology are driven by some dynamical forcing. This is because meteorology is mainly concerned with phenomena associated with the generation and resolution of atmospheric instabilities that can lead directly to disasters, and has therefore dealt with the disturbed component of atmospheric motion. The Radiatively Driven Circulation (RDC) mechanism, on the other hand, is a discussion of the time-mean component, excluding the disturbance component. RDC is the flow required to maintain the time-mean component of the atmosphere in a state of radiative-convective equilibrium, and to ensure the mass continuity. The procedure for determining the flow field dares to say that RDC is, as the name implies, a flow driven by radiative cooling. However, the air mass does not feel any forcing as long as it is moving according to the RDC. In this sense, the RDC is a flow without dynamical forcing. But, if an air mass attempts to deviate from the RDC even slightly, it is immediately pulled back into the RDC flow by dynamical restoring forces (positive or negative buoyancy). In other words, the RDC can be said to be a flow with a strong dynamical restoring force (binding force) locally.

The thermohaline circulation in the ocean is now widely accepted as an essential part of mass transport in the mesopelagic zone, even though it differs from general ocean currents in that it is not driven by wind forcing near the sea surface. The thermohaline circulation may have been relatively easy to accept in the sense that it is driven by (negative) buoyancy forces due to low temperatures and large amounts of dissolved materials. RDC, which transports mass/heat/water vapor without such a direct driving force, is a still more interesting phenomenon than the thermohaline circulation. However, the RDC is not an intuitive flow and requires a bit of imagination and logical reasoning to understand. Because of its physical peculiarities, it is difficult to be accepted by many researchers.