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KINEMATICS OF FLUID FLOW AND CLOUD ORGANISATION

KINEMATICS OF FLUID FLOW AND CLOUD ORGANISATION. VARIOUS CLOUD PATTERNS. NINE TYPE. COMMA TYPE. EYE TYPE. SIX TYPE. KINEMATICS. Kinematics of fluid flow refers to the description of motion of the fluid without reference to the forces that are responsible for such motion.

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KINEMATICS OF FLUID FLOW AND CLOUD ORGANISATION

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  1. KINEMATICS OF FLUID FLOW AND CLOUD ORGANISATION

  2. VARIOUS CLOUD PATTERNS NINE TYPE COMMA TYPE EYE TYPE SIX TYPE

  3. KINEMATICS • Kinematics of fluid flow refers to the description of motion of the fluid without reference to the forces that are responsible for such motion. • Kinematics comes from the greek word meaning "motion". • By kinematics we mean a description of motion of a particular field without regard to how it come about or how it will evolve. • Complete solutions to specific flow problems cannot be obtained from kinematics alone, but a number of important results may be derived & applied. • Kinematics involves two fields • - scalar fields such as pressure, density etc • &- vector field such as wind.

  4. KINEMATICS • Applications of kinematics of fluid flow in meteorology is to understand the organisation of clouds. • Cloud systems gets organised into various patterns like comma, bands, streets, spirals etc. • Such organised cloud features translate without loosing their organised pattern.

  5. WIND Y P(x,y) V v u O X 5

  6. DECOMPOSITION OF A LINEAR WIND FIELD • The distribution of horizontal velocity around a fixed point in space may be expressed by Taylor’s expansions of the x and y components of velocity about the point (xo , ,yo) which serves as the origin of the coordinate system. • At any point in the neighbourhood of the origin

  7. Neglecting higher order derivatives is justified if we consider only the linear distribution of velocity in the vicinity of the origin of the system. [i.e The distance between (x,y) and (xo, yo) being a fraction of the synoptic scale larger distances]. • The fact that fields of motion are actually nonlinear does not invalidate use of these expansions unless the distances x and y are very large.

  8. Thus neglecting the higher order terms, the equations in u and v reduces to:-

  9. WIND FIELD TRANSLATION = u0, v0 VERGENCE DEFORMATION D1 VORTICITY DEFORMATION D2

  10. I II III IV • Term I represents uniform translation of air parcel. • Term II represents expansion ( >0) or contraction ( < 0) about origin. • Term III represents counterclockwise ( >0)or clockwise (< 0) rotation about the origin. • Term IV represents deformation, the changing shape of the fluid element about the origin.

  11. Term I indicates the entire cloud field translation, whereas the shape, size and organisation of specific cloud elements is going to be indicated by terms II, III and IV. • The motion relative to the origin is a composite of velocity divergence, vorticity and deformation at the origin. • It is important to note that very rarely in the atmosphere, the wind field can be composed of pure translation, pure divergence, pure vorticity and pure deformation.

  12. PURE TRANSLATION  = 0  = 0 D1, D2 = 0

  13. DIVERGENCE/CONVERGENCE u0=0, v0=0,  = 0 and D1, D2 = 0  > 0  < 0

  14. VERGENCE AND VERTICAL MOTION

  15. VORTICITY u0=0, v0=0,  = 0 AND D1, D2 = 0  < 0  > 0 C A

  16. ROLE OF WIND FIELD IN CLOUD ORGANISATION • The cloud configuration is best related to the relative wind field. • Divergence/convergence is related to vertical motion of clouds and its areal coverage. • Vorticity & deformation is related to the configuration of cloud organisation.

  17. What are Relative winds? Relative winds are found by subtracting the velocity (direction and speed of movement) of the system from the measured winds.

  18. WIND FIELD AND RELATIVE MOTION E WIND MAXIMUM MOIST DRY Distortion of a line EE due to rotation: (a) At t=0 (thin line) and t=1 ; (b) ) At t=2 E

  19. WIND FIELD AND RELATIVE MOTION Fig : As In Previous Fig but also with translation: (a) Adding vector V to simulate the motion (b) Resultant winds on two diameters only (c ) Flow due to rotation and translation. D is the centre of synoptic winds. C is the centre of rotation. In practice the winds are recorded as in (c.) and the speed of the system is subtracted to get relative winds 20

  20. SIMPLE DEFORMATION ZONE IN STATIONARY SYSTEM • The solid contours are streamlines and the line segment represent wind vectors • The velocity pattern is a cellular combination of vorticity centres with deformation zones between them H L H L H L

  21. DEFORMATION ZONE IN MOVING SYSTEM LEADING N X N D D TRAILING X N X • The total wind vectors do not reveal the deformation zones. • Deformation zones can still be located in the vorticity field. • The wind speeds can be high or low at the deformation zones . • Subtracting the system velocity will in a return to the previous figure.

  22. COMMA CLOUD AND DEFORMATION ZONES D2 J2 • Relative streamlines for an intensifying depression moving slowly northeast • D1 – Low level deformation zone • D2 – High level deformation zone J1 Shaded area represents clouds D1

  23. RELATIVE WINDS & CLOUD ORGANISATION

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