Last updated on July 13th, 2020 at 10:07 pm
“Crystals in the blue sky waits for a testament,
Their wholesome match cloud all judgment.”
Many of us must be aware that banking on weather forecast beyond a stipulated number of days is fatalistic. The issues primarily being data collection and limitations of a computer, alongside the chaotic behavior that our Earth’s climatic system possesses which basically means that any small change in the conditions unaccounted for can bring drastic variation in the end result, play a decisive role in weather forecasting. The clouds play the most important role in these yet-to-be predictive local variations. Not only in the scientific ventures do clouds affect the forecast but also in many literatures their ever-changing form and distribution bring contrast imagination.
Clouds are aerosols consisting of minute liquid droplets, frozen crystals and suspended particles in the atmosphere. The process is sped up by increased saturation of air which is due to parcels of air containing water vapour rising and cooling at dew-point temperatures via convective or cyclonic currents usually allowing adiabatic cooling of water. The process of their formation and influence thereafter cause small yet significant local variations in circulations resulting in the convective currents that make it difficult to initialize and compute all these parameters posing serious difficulties in weather forecasting.
How the clouds form and travel
A cloud is formed when atmospheric water vapor is cooled by vertical air motions condensing on microscopic airborne particles. Between the evaporation of water from the surface and its condensation in a cloud, water vapor is carried along by winds from warmer, moister regions to cooler, drier ones. These convective currents are due to the temperature variations from low to high altitudes as well as from low to high latitudes, which are intensified by the effects of water vapor on radiative heating and cooling and by the transformations of water from liquid or solid into vapor and back because of a high specific heat that water possesses. Since cold air is denser than warm air, temperature differences also give rise to atmospheric motions that work to eliminate the density differences as well. The contrasts in heating, together with the wind circulations, drive ocean currents. A portion of water evaporated from the surface (primarily from the oceans) condenses into clouds and eventually falls as rain or snow. These transformations not only redistribute water but also play an important role in global heat transport.
The processes that control the conversion of water vapor into cloud and precipitation particles are called cloud microphysical processes. The interaction of these processes determines the properties of clouds that, in turn, determine the effect of clouds on the radiative energy exchanges, whether the cloud will produce precipitation, how much and what type of precipitation it will produce, and how long the cloud will last. The formation, evolution, and motion of clouds is determined by the interaction of these cloud microphysical processes with atmospheric motions and radiation emerge to form the field of cloud dynamics.
Role of Clouds in Climate
Clouds have always been signs of the weather to come but mainly obscure our vision. Their most important roles in climate are to modulate Earth’s basic radiation balance and to produce precipitation. Clouds both reflect incoming sunlight and inhibit the radiation of heat radiation from the surface, thereby affecting both sides of the global energy balance equation. Clouds also produce precipitation from water vapor, releasing heat from the surface to the atmosphere. Thus, any changes in clouds will modify the radiative energy balance and water exchanges that determine the climate.
The trouble is that clouds are produced by the climate, specifically the atmospheric winds that are produced by the radiative and latent heating influenced by clouds. This results in a feedback loop. The net effect on the energy balance (temperature of Earth) and water balance becomes hard to determine as it’s the changes in clouds that change the climate which affects in turn cloud formation and distribution.
The Cloud Feedback
The primary energy exchange pathway within Earth’s climate system begins with non-uniform solar heating of the ocean and land surface which disallow local balancing resulting in circulations. Aforementioned behavior of clouds to affect the net energy and water balance indeed affect the circulations and hence their formation itself.
An important consequence of these cloud effects is that timescale for the variation of the energy and water exchanges set by the atmosphere through cloud modulations has a time scale that is very different from the time scale on which the ocean can respond. Thus, the energy and water exchanges fail to balance over shorter time periods as well as small spatial scales, resulting in unforced variations of the climate bringing out the chaos in the system into the picture.
The Net effect on Energy & Water balance
The difficulty of understanding how clouds affect climatic change is that clouds both cool and heat the planet, even as their own properties are determined by this cooling and heating. The minute water particles in clouds reflect between 30 and 60 percent of the sunlight that strikes them, giving them their bright, white appearance. To be in radiation balance Earth would have to be warmer by about 12°C (22°F). The cooling effect of clouds is a blanketing effect: cooler clouds reduce the amount of heat that radiates into space by absorbing the heat radiating from the surface and re-radiating some of it back down. The process traps heat like a blanket and slows the rate at which the surface can cool by radiation. This effect warms the Earth’s surface by about 7°C (13°F). The net effect of clouds on the climate today is to cool the surface by about 5°C (9°F). The balance in the heating and cooling effect produced by the clouds is an utmost necessity for any weather predictions.
Clouds are also part of another important internal heat exchange process involving water phase changes. The atmospheric circulation transports water vapor from place to place. Upon precipitation, the energy released by the condensation heats the atmosphere. Because of the atmospheric transport of water vapor, the precipitation does not locally balance the evaporation, so the water vapor transport is equivalent to energy transport. Thus, the water cycle links the two parts of the radiation balance: the surface is heated by sunlight and cooled by water evaporation, but the atmosphere is heated by precipitation and cooled by terrestrial radiation to space.
Although simple relations may hold between climatic conditions and the radiative properties of certain kinds of cloud, predicting how the global distribution of various kinds of clouds would change warming is complicated by their interaction with regional wind systems. The quest for more data about clouds and climate continues in parallel with the refinement of climate models at local levels. It is a slow-going process: each new piece of information must be incorporated throughout. With certain findings, the computer models themselves may have to be reformulated. But the result should be an increasingly precise understanding of how sensitive the clouds are in response to changes in external forces and what effect those changes would have on the global energy and water balance equation. One must hope that the model building and data collection activities will lead to an understanding of climatic change before that change comes to pass.
” A good forecaster is not smarter than everyone else, he merely has his ignorance better organized. “
“This is the first article in the series of Clouds in judgment. To be able to forecast weather for at least next 12 hours, wait for our next article Clarity in judgment.”