A rise of a meteoroid thermal in the terrestrial atmosphere
|1Chernogor, LF, 1Mylovanov, YB |
1V.N. Karazin Kharkiv National University, Kharkiv, Ukraine
|Kinemat. fiz. nebesnyh tel (Online) 2018, 34(4):53-66|
|Start Page: Dynamics and Physics of Solar System Bodies|
A numerical solution to a set of nonlinear differential equations describing the parameters during the rise of a thermal (speed, radius, and excess temperature) as a function of both height and time has been found. The change in the speed of an upward moving thermal is determined to be not monotonous: first, the speed rapidly increases and the rate of its increase decreases as the air parcel experiences an increasing drag force from the approaching air flow; this speed remains close to a maximum of about 10 — 180 m/s for a long time (tens to thousands seconds) and then it relatively slowly (hundreds to thousands seconds) decreases to zero. The solution has also shown that the more thermic is heated, the greater his size is, and the more rapidly it rises and reaches greater altitudes for a longer time. In the process of uplifting, the radius of a thermal increases by a factor of 6 — 25 times, depending on the initial thermal size and initial thermal temperature, due to the attachment of cool air. The greater the rate of an increase in the radius of a thermal, the greater current radius is. Generally, a thermal of smaller size increases its size by a factor greater than a thermal of bigger size does. Increasing in the radius of a thermal continues to its full stop. The less heated thermals lift up more slowly, attach less amount of cool air, and, consequently, they increase their size to a lesser extent. The model shows that the rate of cooling is proportional to the speed of thermal uplifting and is a maximum when the rate attains a peak value. The thermal heated greater cools more rapidly than the thermal heated less. The rate of thermal cooling comparatively weakly depends on its initial size. The limitations of the model used are discussed, including the assumptions that the atmosphere is uniform and isothermal, the neglect of thermic cooling due to thermal radiation, the winds, and turbulence. Regardless of the limitations, generally, the model agrees with the observations of the uplifting of the thermal formed during the airburst of the Chelyabinsk meteoroid.
|Keywords: altitude of lifting, cooling of thermal, meteoroid, radius of thermal, rate of rising, thermal, time of lifting|
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