Clouds play a large role in the circulation of water, energy, and matter on earth. Therefore, weather and climate predictions can differ greatly depending on how well a model captures clouds (and precipitation). For example, it is necessary, when considering the recent issue of warming and its impact on the global environment, to conduct research on several types of clouds including “thick and thin clouds,” “ice and water clouds,” “Isolated cumulus like a cotton candy and stratus with a large area”. This is because the roles of these clouds broadly differ from one another in the global environment. However, handling of cloud droplets and particles, internal and external cloud flows, and radiation budget calculations under atmospheric conditions where clouds exist are insufficient in current models. This is one of the key elements of uncertainty among weather and climate models. For this reason, progress has been made globally on the development of numerical “cloud resolution models,” and “satellite-mounted cloud radars.”
Of course, those who research clouds must also include the “polluted atmosphere,” which includes aerosols that act as the nuclei for the formation of cloud particles and ice crystals. Calculations of “clean” atmosphere flows can be performed using fluid dynamics, but we ought to make fundamental research progress from the particle dynamics (a term I coined) and multiphase flow perspectives for our “polluted global atmosphere”. Merely using fluid dynamics, we would calculate changes in air temperature and humidity for a rising air parcel using continuous equations and thermodynamic equations, and determine cloud formation at which relative humidity reaches 100%. However, one cannot determine the cloud particle’s size distribution for the body of the cloud using this method. When the cloud’s particle distribution is indeterminable, the formation rate of precipitation and the cloud’s radiating characteristics are also indeterminable. It is clear, through simple trial calculations, a small percentage change in the cloud particle size can have much larger impact on the warming than doubling of CO2.
Moreover, cumulus clouds, formed inside the atmospheric boundary layer (below an altitude of 1km) are also important when considering the connection between clouds and ecosystems in which we are interested. Clouds sometime form when the boundary layer undergoes daily changes due to sensible and latent heat fluxes from the land surface. Of course, sensible and latent heat fluxes vary largely by land surface conditions and the distribution of vegetation. On the other hand, it is known that the formation of fair weather cumulus clouds creates an advantageous photoenvironment for the growth of vegetation. For example, fair weather cumulus clouds moderate the rise and fall of air temperature above ground during the day and night respectively. Moreover, it is easier, relative to direct light, for light scattered by clouds to reach the inside of a forest. Meanwhile, it is also known that the existence of fair weather cumulus clouds increases the net carbon assimilation of forests. Recently, migrations of birds and butterflies, broad movements of grounded insects, and the daily activities of birds have also been tied strongly to atmospheric flows at the boundary layer. In this way, research themes focused on “clouds” will be even more closely linked to other fields than research on rain or snow.
by Y. Fujiyoshi