Clouds Formed by Thermals Arising and Evolving Under the Influence of the Coriolis Force

In the presented study, a ‘mushroom-like’ cloud structure in the atmosphere of the Northern Hemisphere has been studied. Examples of such a structure are shown and compared with the result of a simple analytic model of thermals developing in a gravitational field of the rotating Earth. Most generally, this structure can be described as a consequence of the interaction of the Coriolis force at a certain degree of atmospheric instability. The conditions for the occurrence and development of single thermal have been analyzed. For this purpose, the parcel theory of thermal formation is utilized. The studied cloud structures are relatively rare, which makes it difficult to determine the conditions for their appearance. These clouds are mostly observed in the cool part of the year. Subsequently, the contrast between the temperature in the tropical part of the ocean and that in the polar regions favors the occurrence of horizontal convection caused by the Coriolis force. It was found that the instability index, introduced by the authors in another study, should have values below minus one. The outcomes of the study suggest that there is an optimal range of temperature difference between the thermals and environment, as well as suitable wind and a level of instability for the development of the considered phenomena.