1. TROPICAL CYCLONES

2. TROPICAL CYCLONE FORMATION
Introduction
Definition
Regions of formation
Classification
Seasonal Genesis Parameters
Conditions favorable for formation
Life cycle of tropical cyclones
Structure of tropical cyclones
TC Energetics
Eye and Spiral bands
Movement
Conclusion

3. INTRODUCTION
The formation of tropical cyclone is a relatively rare event and over the globe, there are about 80 tropical cyclones forming each year.
Riehl (1954) noted that tropical cyclones often develop out of pre-existing circulation.
This provides large scale upward motion and moisture transport which is a pre-condition for their genesis.
Surges in low level flow have been identified as an important triggering mechanism.

4. DEFINITION
Tropical Cyclone is a non frontal synoptic scale low pressure system over tropical or sub tropical waters with organised convection (ie Thunder storm activity) and a definite cyclonic circulation (Howard 1993)
A tropical cyclone has surface winds greater than 17m/s (34 kts)

5. DEFINITION (Contd) Tropical depression with winds up to 33 kt.
A closed warm core circulation system of at least 05 deg. Diameter which extends vertically through most of the troposphere with little vertical slope and relative vorticity in inner 100 – 200 km radius being greater than 100x10-06/sec, pressure deficit at the centre being greater than 15 hpa.
Tropical depression with winds up to 33 kt.
Tropical storm with winds of 34 to 63 kt.
Hurricane or typhoon with winds of 64 kt or more.

6. DEFINITION (IMD)
It is an intense vortex or a whirl in the atmosphere with very strong winds circulating around it in an anti clockwise direction in the northern hemisphere.
The word cyclone is derived from the Greek word “Cyclos” meaning the coil of a snake.

7. GLOBAL DISTRIBUTION OF TROPICAL CYCLONES
For the year as a whole percentage frequency in different areas of tropical ocean is:-
Western North Pacific %
North Indian Ocean - 15%
South Indian Ocean - 14%
West Atlantic Ocean - 12%
Pacific Ocean (Not Equator) - 11%
South Pacific %
North & West Antarctica - 07%

8. 30%
12%
11%
15%
14%
07%
11%

9. CLASSIFICATION OF CYCLONIC DISTURBANCE
SL NO
TYPE OF DISTURBANCES
ASSOCIATED MAX SUSTAINED WIND
T VALUE
SEA CONDITION
WAVE HEIGHT IN METERS 01
Low Pressure Area
Not exceeding 17 Kts (<31 Kmph)
Mod rough 02
Depression
17-27 Kts (31-49 Kmph)
1.5
Very rough 03
Deep Depression
28-33 Kts (50-61 Kmph)
2.0
High 04
Cyclonic Storm
34-47 Kts (62-88 Kmph)
Very High 05
Severe Cyclonic Storm
48-63 Kts ( Kmph)
3.5
Phenomenal 06
Very Severe Cyclonic Storm
64-89 Kts ( Kmph)
>14.0 07
Extremely Severe Cyclonic Storm
Kts ( Kmph) 08
Super Cyclonic Storm
>120 Kts (>221 Kmph)
>6.5

10. CAUSES OF DEVASTATION DUE TO CYCLONIC STORM
Winds: Gust, Change in direction with passage of eye over land. Friction reduces sustainable wind but not peak gust, resulting in widening of gap between peak and lull.
Creats strong negative pressure forces on lee side of structure.
Stronger in the right semi circle wrt direction of motion.
Rainfall: Very heavy and spread over a large area (some times >30cm in 24 hrs) resulting in flood.

11. CAUSES OF DEVASTATION DUE TO CYCLONIC STORM (Contd)
Storm Surge: Due to winds massive pooling of sea water lead to sudden inundation and flooding of coastal regions. This combined with the astronomical high tide could cause even greater devastation.

12. SEASONAL GENESIS PARAMETERS
Gray (1975) suggested that tropical cyclone formation will be most frequent in regions and in seasons where SGP, which is the product of six primary genesis parameters, is maximum.
SGP = (dynamic potential) x (thermal potential)
= Z X F X 1/s X E X S X H, WHERE,
Dynamic potential is the product of vorticity (z), coriolis force (f) and inverse of vertical shear (s).
The thermal potential is the product of ocean energy (e), moist stability (s) and humidity (h).

13. SEASONAL GENESIS PARAMETERS
Low level relative vorticity (Z)
Z measures low level convergence.
Tropical cyclones require a continuous import of mass, momentum and water vapour which requires low level convergence.
Hence, large positive relative vorticity at low level increases the potential for cyclone genesis provided other conditions are favourable.
Coriolis parameter (F)
It is a measure of the influence of earth’s rotation.

14. SEASONAL GENESIS PARAMETERS
Geostrophic consideration indicates that pressure gradient and winds near the equator are very weak which is unsuitable for intensification of cyclones.
Other factors being favourable, tropical cyclone genesis is directly related to strength of coriolis parameter and its weak value near the equator is unfavourable for storm formation.

15. SEASONAL GENESIS PARAMETERS
Inverse of vertical shear (1/s)
Vertical wind shear measures the tropospheric ventilation.
Tropical cyclones form under conditions of minimum vertical shear of the horizontal wind between the lower and the upper troposphere.
Ocean thermal energy (E)
E is a measure of moisture feed.
Palmen (1945) stated that tropical storms form only in those oceanic regions away from equator where the sst is above 26 – 27 deg. Celsius.

16. SEASONAL GENESIS PARAMETERS
Moist stability parameter (S)
Gradient of potential temperature measures the instability of atmosphere.
Cb convection provides the mechanism for coupling between lower and upper troposphere.
It is observed that large values of potential temperature are associated with strong conditional instability.

17. SEASONAL GENESIS PARAMETERS
Hence, cyclone genesis is directly related to potential buoyancy and this buoyancy is specified by difference in potential temperature between surface and 500 hpa.
Mid troposphere relative humidity (H)
Formation of intense Cb over tropical oceanic regions does not occur until mid-tropospheric RH is more than 50 – 60%.
It can be inferred that cyclone genesis is directly related to average rh between 500 and 700 hpa.

18. CONDITIONS FAVORABLE FOR THE FORMATION OF A TROPICAL CYCLONE
Develop in the vicinity of ITCZ, where relative cyclonic vorticity is already present. In maritime air mass over sea areas where SST >= 270C and over lying tropical atmosphere is convectively unstable.
Presence of easterly wave
Presence of wave pattern in the upper troposphere which would cause upper level horizontal velocity divergence and hence lower level convergence near the storm area.

19. CONDITIONS FAVORABLE FOR THE FORMATION OF A TROPICAL CYCLONE
In climatological favorable regions there should be weak vertical wind shear, generally the shear of Zonal flow between hPa should not exceed 10 m/s.

20. LIFE CYCLE OF A CYCLONIC STORM
Formative Stage
The formative stage covers the period from the genesis of cyclonic circulation as a low pressure area through the stage of depression till it reaches the intensity of severe cyclonic storm.
At the end of this stage, the eye and the wall cloud are formed.
This stage is often referred to as ‘unsettled conditions’.

21. LIFE CYCLE OF A CYCLONIC STORM
Immature Stage
During this stage, the central pressure rapidly falls and winds strengthen.
The central pressure and winds reach maximum limit.
The cloud and rainfall patterns get organised into narrow bands spiraling inwards.

22. LIFE CYCLE OF A CYCLONIC STORM
Mature Stage
The main feature of this stage is that the entire circulation expands while pressure remains nearly constant at the centre. This stage exhibits four distinct areas:
Eye
Area is about 0 to 20 km in diameter characterised by calm winds and clear to partly cloudy skies. This forms the area of lowest pressure.
An Inner Ring Of Hurricane Wind
Inner ring of 50 to 60 km width with hurricane winds encircling the eye within which violent squalls with torrential rain occur. This forms the most dangerous part of the storm.

23. LIFE CYCLE OF A CYCLONIC STORM
Outer Storm Area
This area is situated asymmetrically to pressure centre expanding to 400 km or so, wherein winds reach to gale force (22 to 47 kt). Strongest winds occur to the right of the cyclone track.
Outermost area of weak cyclonic circulation.
Decaying Stage
During this stage, the system weakens which may be due to cyclonic storm entering land or moving into regions of cold waters.

24. LIFE HISTORY OF TROPICAL CYCLONE
Neighborhood of ITCZ or near equatorial trough, relative cyclonic vorticity is already present.
Easterly waves (one of it) helps in the formation of a cold core low. (Relatively cold air is lower layers and relatively warmer air aloft. Intensity maximum when the system changes from being relatively cold to relatively warm )

25. LIFE HISTORY OF TROPICAL CYCLONE
Existence of Cyclonic Vorticity in the frictional layer induces horizontal inflow and vertical upward motion, which is initially dry adiabatic.
Above LFC it is warmer than environment, rises moist adiabatically.

26. LIFE HISTORY OF TROPICAL CYCLONE
The relatively warm air accelerates upwards, which induces inward movement of cyclonically rotating rings of air. These air rings spin faster as they travel inward through conservation of angular momentum.
The level of transition between warm and cold sector of low descends down and the system becomes more intense and finally warm core descends down to the sea level and the entire vortex is warmer than the environment. This in most cases is the severe storm stage (>48 Kts)
Severity of winds, rain and pressure deficiency at the centre of the system increases.

27. TRANSFORMATION FROM A COLD CORE SYSTEM TO A WARM CORE SYSTEM
Latent heat of condensation released inside the cloud.
This heat transported vertically under buoyancy and horizontally outward through detrainment of cloud air.
Cumulus induced subsidence in the cloud free region causes general warming through out the Troposphere.
On becoming a SCS, subsidence and warming also take place at the centre (eye of the storm).

28. Each cloud entrains un saturated air units lower part and detrains saturated air containing water particles near its upper parts. The detrained water particles evaporate on the cloud free environment and makes it cooler and more moist in the process.
Below cloud base falling precipitation evaporates and causes evaporation cooling.
Radiative process cool the entire troposphere by nearly 10C / day.
As the system intensifies the heating due to the condensation and subsidence more than compensate for the evaporational and radiative cooling.

29. EASTERLY WAVES THAT ARE FAVORABLE FOR CYCLOGENSESIS.
Typically have periods of 3.5 days and wavelength of 2000 to 3000 km.
MESOSCALE CONVECTIVE SYSTEM
MCS
700 KM
2500 KM

30. EC- EXTREME CONVECTION
MCS
EC area
250 KM
CLUSTER
700 KM

31. CRITICAL LAYER FOR WAVES IN LATITUDINAL SHEARCL U Y
dξa/dy =β-d2u/dy2
d2u/dy2 <0
Jet Max

32. Stable easterly waves have critical latitudes,CL just outside jets inflection point where gradient of absolute vorticity or “effective” ß is zero.
Unviable waves have there critical latitudes just inside the latitude of injection points.

33. SAL CL
MOIST INFLOW
MOIST
TROUGH
SCHEMATIC OF THE POUCH
Jet

34. Wave breaking or roll up of cyclonic vorticity near critical surface layer in the lower troposphere provides favorable environment for aggregation of vorticity seedling for TC formation.
In the CL the air is repeatedly moistened by deep convection and protected.

35. Descending motion occurs at the top of the TC and the warm core penetrates downwards.
The eye of the storm forms, which clear of all clouds in Very Severe Cyclone and broken clouds may be seen floating in the eye in the case of moderately severe cyclone.
The cyclonic vortex interacts and drifts with the general air current.
On hitting coast it is cut off from, the warm moist air and encounters irregular terrain leading to frictional dissipation.

36. Weakens into a cold core depression and disappears.
It weakens also on encountering cold SST.
Occasionally it re-intensifies as it reemerges from land to sea.
On some occasion the TC moves to sub-tropical and extra tropical latitudes and assumes the characteristics of ETC.
Total life period from weak cyclonic vortex to full hurricane stage and then to dissipation may vary from couple of days to about a fortnight.

37. CISK THEORY TC DEVELOPMENT
Charney and A Eliassen(1964)- Proposed an asymmetric balance theory for co-operative interaction between a field of deep cumulus clouds and an incipient, large scale cyclonic vortex.
It highlighted the role of friction in supporting the amplification process.
Frictional convergence in the moist surface boundary layer results in supply of latent heat to the system.

38. CISK THEORY (Contd)
Latent heat release by the cumulus convection is proportional to the vertically integrated convergence of the moisture through the depth of the troposphere, which happens mainly in the boundary layer.
Large scale circulation is to replenish the boundary layer moisture by adverting low level moisture ( and hence CAPE) from the environment. It completely overlooks the central role of surface moisture fluxes in the accomplish the re moistening.

39. CISK THEORY (Contd)
Purely by CISK theory cyclonic intensification would be just un likely to occur over land and over sea, contrary to observation.

40. OOYAMA MODEL OF CO-OPERATION INTENSIFICATION(1969&1997)
Tropical Cyclone represented by asymmetric, balanced vortex in a stably stratified, moist atmosphere.
If a weak cyclonic vortex is initially given, there will be organised convective activity in the region where the frictionally induced inflow converges.
Differential heating due to the organized convection introduces changes in the pressure field, which penetrate a slow transverse circulation in the free atmosphere.

41. OOYAMA MODEL OF CO-OPERATION INTENSIFICATION(1969&1997)(Contd)
The resulting increase in cyclonic circulation in the lower layer and the corresponding reduction of the central pressure will cause boundary layer inflow to increase.
Thus move intense convective activity will follow.
Positive feedback process between the wind speed dependent moisture fluxes and tangential wind speed of the broad scale vortex.

42. OOYAMA MODEL OF CO-OPERATION INTENSIFICATION(1969&1997) (Contd)
It re-establishes balance between the pressure and motion field.
If the equivalent potential temperature of the boundary layer is sufficiently high for moist convection to be unstable then transverse circulation in lower layer will bring in more absolute angular momentum than is lost to the sea by surface friction.

43. MAIN ASPECTS OF CISK AND OOYAMA CO-OP INTENSIFICATION THEORY
The main spin up of the vortex occurs via the convergence of angular momentum above the boundary layer.
The boundary layer plays an important role in converging moisture to sustain deep convection, but it dynamical role is to decrease the spin up.

44. WIND INDUCED SURFACE HEAT EXCHANGE (WISHE) THEORY OF CYCLONIC INTENSIFICATION (Emmanuel – 1994)
Atmosphere is assumed to neutrally stratified along surface of constant angular momentum.
Surface features of heat and moisture in the boundary layer important for convective temperature perturbation in the troposphere.
The surface fluxes are wind speed dependant therefore determined by vortex scale flow .
This model emphasis air-sea interaction.

45. OOYAMA MODEL OF CO-OPERATION INTENSIFICATION(1969&1997)(Contd)
The vortex must exceed certain threshold intensity for amplification to proceed.
Non necessity of CAPE in the storm environment for amplification.
This theory has gained widespread acceptance in recent year.

46. VORTICAL HOT TOWER (VHT) THEORY OF CYCLONIC INTENSIFICATION
Moist air flow rises out of the boundary layer and cools, condensation occurs in some grid columns inside radius of maximum tangential wind.
Deep convective up draughts of the order of 5m/s seen at 850 hPa

47. VORTICAL HOT TOWER (VHT) THEORY OF CYCLONIC INTENSIFICATION (Contd)
These up draughts rotate cyclonically around vortex centre and have life of about 1 hr, called VHT
They develops strong cyclonic vortocity dipole inward and a weaker anticyclonic vortocity dipole outward of the storm. VHT seen mainly during the intensification stage.

48. STRUCTURE OF MATURE TROPICAL CYCLONE
Franks Composite picture – 1977
Pacific Typhoon (248 Storm)- 143 of which attained Cyclonic Intensity.
Satellite Picture
Rainfall Data of several stations including islands
18000 soundings of 30 stations.
Studied in the region N lat, 19 neutral levels up to 50 hPa. Compositing done in 150 lat cylindrical grid with centre of storm as origin.

49. SCHEMATIC VIEW OF A TROPICAL CYCLONE50
100
150
200
250
300
350
400
450
550
650
750
850
950
06 Radial Sections
: Eye and Eye wall (d) 4.00 – : Moat region
: Inner rain band area (e) : Outer region
: Outer Convection area (f) : Outer region
P (hPa)
Cirrus Shield
Eye
Eye wall
Inner Rain bands
Outer Rain bands
MOAT
Outer Circulation

50. STRUCTURE SCHEMATIC VIEW

51. STRUCTURE CROSSECTIONAL VIEW

52. PRESSURE FIELD
In terms of geopotential anomaly, the intensity of TC is maximum near the sea level and decreases upwards.
In the upper troposphere, the low pressure area becomes a high pressure area.(150hPa)

53. HORIZONTAL WIND FIELD
Tangential wind is one of the most important parameters of tropical cyclone.
Broadest in lower troposphere. At 750hPa extends to r=140 latitude.
Shrinks to r = 70 latitude at 300 hPa and to r = 40 latitude at 200 hPa.
Anticyclonic flow seen above this region of cyclonic flow.
Speed of cyclonic tangential is maximum at the top of PBL( hPa)
Weak wind field is 5 ms-1 width the eye.
Outside eye wind speed increase rapidly with maximum inside the cloud wall.

54. TWO DIRECTIONAL CROSS SECTION OF VΘ (TANGENTIAL WIND)50
100
150
200
250
300
350
400
450
550
650
750
850
950
r= Degrees latitude
Temperature Anomaly (T-Tr=140)
Vθ (m/s)
P (hPa)
-12
-08
-04
-00 04 08 12 16 20 24
TWO DIRECTIONAL CROSS SECTION OF VΘ (TANGENTIAL WIND)

55. THERMODYNAMIC STRUCTURE
Throughout the troposphere warmer than surrounding
In the lower stratosphere, TC are slightly cooler than their surroundings. At 125 hPa it becomes a cold core anti-cyclonic vortex.
Max temp anomaly seen at 300 hPa. It increases inwards exceeding 100 C and becoming as large as 150 C in the eye.
In the middle and upper troposphere, the temp on the eye may be 070 C at 0.7 degree lat radius.
Temp gradients in the boundary layer are weak.

56. Temperature Anomaly (T-Tr=140) -250
100
150
200
250
300
350
400
450
550
650
750
850
950
r= Degrees latitude
Temperature Anomaly (T-Tr=140) -2 2 4 6 8
P (hPa)

57. RADIAL WIND
There is an inflow in the lower troposphere and outflow in the upper troposphere.
Max inflow inside PBL at 950 hPa
Max outflow at upper temp 150 hPa
In the layer hPa there is inflow at r>= 40 Lat which at r= 20 Lat the radial flow is indifferent iro direction.
Angle of inflow decreases with height being near surface but only 50 at 850 hPa.

58. HORIZONTAL VELOCITY DIVERGENCE
In the region r=00 to 20 there is distinct low level convergence & upper level divergence.
Upward vertical motion seen throughout the troposphere.
In the region r=20 to 40, the values of low level convergence and upper level divergence is lesser. Convergence seen up to 300hPa and upward vertical motion throughout the troposphere.
In the 40 to 60 radial band there is divergence in the lower troposphere and convergence from hPa. There is a weak subsidence and there is outflow into the field of the storm from this region.

59. RELATIVE VORTICITY FIELD
At all radii and at all levels above PBL and up to 200 hPa cyclonic vorticity decreases with height.
At r=20 the relative vorticity becomes anti cyclonic above 250 hPa.
At r=40, it is anti-cyclonic above 550 hPa
At r=60, 80,100 the relative vorticity is anti-cyclonic at all levels in the troposphere.

60. RAINFALL FIELD 3.17 cm/day 10.0 cm/day 8.17 cm/day r= 40 r= 20

61. DIURNAL VARIATION OF RAINFALL
LT- Max rainfall intensity at hrs and Min rainfall intensity at1800 h.
0.12
0.10
0.08
0.06
0.04
0.02
Rate of Rainfall
Local Time

62. BUDGET OF RELATIVE ANGULAR MOMENTUM IN A TROPICAL CYCLONE
For a Unit mass of air at a distance r from the centre of a TC, the absolute angular velocity around the cyclone centre is
=Ω Sinϕ - Vθ/r
Ф-lat
V θ = Tangential velocity
The abs angular momentum
= r(ΩSinФ-V θ /r)= Ωr2 SinФ+rV θ
We know, f=2 ΩSin Ф, viz Coriolis parameter

63. BUDGET OF RELATIVE ANGULAR MOMENTUM IN A TROPICAL CYCLONE
Eqn fr2 /2 +rV θ
rV θ = Relative angular momentum
fr2/ 2=
Due to friction in lower boundary , a TC continuously loses angular momentum
For TC to be in steady state / initially external supply of angular momentum is necessary to replenish frictional losses.
To understand this budget, Frank (1977) considered 09 vertical layers of 100 hpa thickness from surface to 100 hpa and six radial sections from r=00 to r=100

64. SECTORIAL BUDGET OF RELATION ANALYSIS MOMENTUM
RELATIVE ANGULAR MOMENTUM BUDGET
o o o o o
-6.26
-0.57
6.83
+.31
-2.84
2.53
3.48
-6.51
3.03
10.26
-10.12
+.14
11.67
-11.53
.14
13.99
-12.90
1.09
-6.42
-.31
13.56
-1.07
-1.56
5.16
.61
-4.05
6.47
5.32
-6.03
.57
5.11
-6.47
1.22
5.28
-7.88
1.51
-.88
-.12
6.16
.50
-.61
6.58
1.82
-.26
.99
.26
-.95
1.91
.33
2.74
-0.8
.05
6.19
1.03
.04
5.51
1.27
-.03
2.23
.11
-.38
2.18
.22
-.25
2.77
-.75
6.94
1.40
4.36
1.29
-.16
3.36
.70
-.44
1.92
1.24
-.82
2.35
-1.27
-.11
8.32
1.62
-.52
3.26
1.14
-.64
3.86
-.80
2.15
1.77
-.53
8.85
2.14
-.04
1.16
.86
.16
4.56
.46
1.94
.74
-0.26
7.25
6.05
4.22
1.28
3.35
4.17
2.02
5.03
-0.30
1.90
1.76
.64
-0.55
1.59
.25
12.93
.62
7.50
12.67
3.30
12.62
4.88
5.81
15.72
-0.73
5.72
11.15
0.84
5.82
7.30
-0.67
6.27
5.35
100
200
300
400
500
600
700
800
900
sfc

65. RELATIVE ANGULAR MOMENTUM BUDGET
(1.2)
-1.2
-0.1
1.3
+0.4
-3.8
3.4
(0.8)
16.2
-30.3
14.1
(15.4)
79.6
-78.5
1.1
(95.0)
126.7
-125.2
1.5
(221.7) (417.0)
195.3
-180.1
15.2
2.6
-1.5
-2.1
7.0
(2.7)
2.8
-18.8
30.1
(01)
41.2
-46.8
4.5
(41.3)
55.5
-70.2
13.2
(96.8) (170.5)
73.7
-110.0
21.1
-.2
8.4
2.3
-2.8
30.6
(1.1)
-2.0
7.6
(15.2)
-10.3
20.7
(18.0).(22.6)
4.6
-21.8
38.3
-0.2 .1
8.5
(0.2)
4.8 .2
25.6
(4.6)
9.9
17.3
(14.5)
1.2
-4.2
23.7
(15.7) (18.8)
3.1
-3.5
38.7
-1.0
9.5
(1.0)
6.5
20.3
(5.5)
10.0
26.1
(15.5)
-4.7
20.8
(23.1)(40.4)-.82
-11.4
32.8
-1.7
11.4
(1.7)
7.5
-2.4
(5.8)
8.8
-5.0
29.9
(14.6)
6.2
-8.7
23.3
(20.8)(40.3)
19.5
-11.7
24.7
-.8
12.2
(.8)
5.4
(9.2)
6.7
35.4
(15.9)
5.0
(20.9)(31.2)
10.3
-3.6
18.0
(14)
1.4
0.1
5.7
1.7
(7.1)
19.4
9.4
23.4
(26.5)
-2.3
14.7
47.8
(24.2)
8.9
19.1
6.9
(33.1)(25.4)
-7.7
22.2
3.5
(2.4)
2.4
17.4
17.1
19.8
22.7
27.0
73.1
(42.5)
-5.7
44.4
86.5
(36.8)
9.1
63.2
79.2
(45.9-)(36.5)
-9.4
87.5
74.7
100
200
300
400
500
600
700
800
900
sfc
0.7o 2o 4o 6o 8o
10o

66. BUDGET OF KINETIC ENERGY IN A TROPICAL CYCLONE
The KE equation is given by
Ək/Ət= .(Vk)-Ə/Əp(ωk)- V. Ф+V.F
K is KE of unit mass means ½ |V2 |
Ф=gz is the PE
F is the frictional force + internal friction for steady state cyclone Ək/Ət=0.
.(Vk) is calculated from radial inflow and outflow of V2/2 across vertical cylindrical boundaries.

67. BUDGET OF KINETIC ENERGY IN A TROPICAL CYCLONE
-Ə/Əp (ωk) is the convergence of vertical flux of k calculated on the assumption that ω=0at the sea surface and also p= 100mb.
–V. Ф gives the generation of KE through horizontal motion component from high pressure to low pressure.
Additionally one has to consider the eddy terms

68. FRANK’S (1977) BUDGET ESTIMATE
-6.6 Horizontal Convergence
+2.0 –V. Ф
-0.6 Internal Dissipation
+0.9 Vertical Flux Required Eddy Generation
-.9
+1.4 Horizontal Convergence
+.6 -V. Ф
-1.6 Internal Dissipation Required Eddy Generation
+.4 Vertical flux
-0.4
Horizontal Convergence
V. Ф Required Eddy Generation
Internal Dissipation
-2.9 Surface Dissipation
+4.3
+0.1
+1.7

69. Similarly outward flow decreases relative momentum of the cyclonic vortex.
Makes positive contribution in the lower levels of inflow and negative contribution in the upper region of outflow.
For steady state cyclone the total contribution of the torque integrated along the vertical could be zero i.e. mass inflow= mass out flow.

70. CORIOLIS TORQUE ON MERIDONIAL STEERING CURRENT
Coriolis steering current from S to N in which embedded cyclone vortex moves as a whole in the NH
ƒ north > ƒ South
Deflects S- N current to east
Hence net deflection in the anti-cyclonic sense is spin down of storm
For N –S steering current
ƒ North> ƒ South
Deflects N – S current to the West.
Deflection in the cyclonic sense i.e. spin up of the storm.

71. OVERALL QUALITATIVE PICTURE OF TC ENERGETICS
Tropical Cyclone is a warm core system.
Direct circulation of warm air rising and cold air sinking takes place except in the eye region.
KE of horizontal motion is generated by horizontal radial flow from high to low pressure.
Generation of KE of horizontal motion balanced by frictional dissipation and outflow of energy from cyclone area.

72. Radial temperature product on available PE of the system maintained by
Frictional dissipation of KE at lower layers and internal dissipation both play an important role in the TC dissipation.
Outflow of energy takes place in the upper tropo associated with outflow of mass.
Radial temperature product on available PE of the system maintained by
Release of Latent heat of convection
Radiative processes
Flux of sensible heat from underlying warmer sea surface.

73. DIURNAL VARIATION IN INTENSITY OF TROPICAL CYCLONE (HOBGOOD 1986)
Tropical Cyclone dev in regions where atmosphere is initially conditionally unstable. During dev the lapse rate becomes saturated neutral and remains so until changes occur in external environment.
During dev radiative processes also affects lapse rate.
During night cloud bottom receives long wave radiation from emits nearly equal amount back to the surface, hence no change in energy of cloud bottom

74. During night top of cloud emits more radiation than it receives then cloud top cooler
Thus the lapse rate through the cloud increases at night leads to increased height and aerial extent of cirrus canopy.

75. During day bottom of cloud not affected by radiative processes, but top of cloud receive greater SW energy than long wave it emits. Thus cloud tops warmer and decreases lapse rate through the cloud, reducing intensity of convection.
Away from the centre in the cloud free region the thin cirrus canopy radiative process lead to subsidence.

76. HOBGOOD (1986)
As storm develops, contribution of radiative process becomes relatively small compared to total energy budget of the storm & diurnal fluctuations becomes less pronounced.

77. FORMATION OF A HURRICANE EYE
In severe vortices (>35 ms-1) there exist two meridional cell circulation; outer & inner
In the outer cell there is downward motion in the outer region and upward motion in the inner region
In the inner cell there is upward motion in the outer region and downward motion in the inner region
The two meridional cell circulation have there common links of upward motion as in a cloud wall of TC.

78. MALKAN & KUO (1958, 1959) HYPOTHESIS
Inward diffusive transport of cyclonic angular momentum from cloud wall to centre.
By conservation of angular momentum the tangential wind in the eye region becomes very strong and super gradient.

79. SPIRAL BANDS

80. SPIRAL BANDS Two bands generally observed spirally in
Width of the order of 50km near the outer periphery of the cyclone contracting outwards
Hundreds of kilometers in length.
Shape: Approximately form of angular spiral, the angle of inflow being of the order of 15o .
Cellular structure along the length of rain bands. There are ellipsoidal shape areas about 20 km long and 5 km wide, having heavy convection and heavy precipitation of (1-4.5 cmh-1) and even more, with gap regions with light precipitation of ½ cmh-1

81. The rain band is a region of strong horizontal shear of wind.
Between the precipitation cover and gap regions are kinks (bulges and clifts) in the air flow and pressure field as if there are waves in the gravity current.
Upwind edge of bands are mainly convective clouds and down wind edges is stratiform.
Strong inflow of about 15ms-1 till 2 km and changing to outflow at 4 km becoming 15ms-1 6.4km.

82. MOVEMENT

84. TRACK OF
CYCLONIC STORM

85. MOVEMENT What Causes A Tropical Cyclone To Move?
It has been proven that because a tropical cyclone has cyclonic vorticity throughout much of the troposphere, it will move towards the area of max ∂ζ/∂t.
Therefore, physical processes which cause the vorticity distribution to change to lead to a change in the movement of a tropical cyclone.

86. MOVEMENT

87. MOVEMENT
In particular, a tc embedded in a non-quiescent environment will have an area of max ∂ζ/∂t downstream of the direction of the environmental flow due to the advection of ζ.
This is like an object flowing along a stream, being steered by the stream flow.
The environmental flow is, therefore, often referred to as the steering flow and the component of motion due to this advective process is called steering.

88. MOVEMENT
Since ∂ζ/∂t depends on other factors as well, steering only contributes to part of the motion of the TC.
However, in general, unless the environment is very weak, steering explains a very large part (> 80%) of the motion. In a weak environment, the advection & convergence of planetary vorticity becomes important. This is known as the β-effect.
Consider the case in which the environmental flow is zero and the atmosphere is barotropic. Then, ∂ζ/∂t is max to the west of the cyclone.

89. MOVEMENT
In a weak environment, the advection and convergence of planetary vorticity becomes important. THIS IS KNOWN AS THE β-effect. Consider the case in which the environmental flow is zero and the atmosphere is barotropic. Then, ∂ζ/∂t is max to the west of the cyclone.
Physically, this is because β (= df/dy) Is constant and the meridional component is max to the west of the cyclone. However, an increase in ζ to the west and a decrease to the east will induce a secondary circulation leading to a northward motion. The combined effect, therefore, produces a northwest- ward motion.

90. ROSSBY  EFFECT
Consider a circular symmetric cyclonic vortex in the NH Lat.
R= Outer boundary of the vortex beyond which air does not participate in the vortex motion.
r, θ, Z = Cylindrical co ordinates, Z being measured from sea level θ =0 point W E direction
= Relative angular velocity, at a distance r from the centre. It can be a function of r but not θ.
F = o+ y - o+ r Sin θ
o = coriolis parameter at the centre

91. N-S MOVEMENT
 increases northward, hence then is lack of balance of forces. North of the vortex centre coriolis force is greater than pressure gradient force whole to south it is vice-versa but to the north and south, there will be a net component of force south to north at every point of the vortex.
This will give a northward component of acceleration and hence a movement of the vortex as a whole to the north to the NH.
Similarly in the Southern Hemisphere the cyclonic vortex will tend to move south ward (pole ward).
Anticyclonic vortices will tend to move equator ward.

92. E-W MOVEMENT(NORTHERN HEMISPHERE)
Consider radial inflow N to S in northern half and S to N in the southern half of the cyclone.
Coriolis force will deflect the flow towards right and as  would be greater to the north of the vortex , the net deflecting force would be from E-W
Then the cyclonic vortex in the NH will tend to move E to W in westward.

93. MOVEMENT
If the steering component is now added, the motion will depend on the direction of the steering flow.
Thus, a tropical cyclone will move in a direction and with a speed different from those of the steering flow. This deviation depends on the direction of the steering flow.

94. MOVEMENT

95. MOVEMENT Forecasting Tropical Cyclone Motion Persistence.
The future motion of a tropical cyclone is the same as its present & past motion.

96. MOVEMENT Forecasting tropical cyclone motion climatology.
The future motion of a tropical cyclone is the average of the directions & speeds of all tropical cyclones occurring within the same grid box and at the same time of the year as the current cyclone.

97. MOVEMENT Forecasting tropical cyclone motion
Climatology-persistence. Two ways:-
(a) combining the persistence and climatology forecasts by using various weights. The most common is 0.5 for each of the forecasts.
(b) Using a stepwise multiple regression technique. The forecasts derived from this technique is known as the cliper (climatology-persistence) forecast.

98. MOVEMENT Forecasting Tropical Cyclone Motion Analog.
The current tropical cyclone will behave similarly to all previous tropical cyclones situated at the same location with the same intensity and at the same time of the year.
NOTE THAT ALL THE ABOVE TECHNIQUES DO NOT USE SYNOPTIC INFORMATION (i.e. THE ENVIRONMENT OF THE TROPICAL CYCLONE).

99. MOVEMENT Forecasting tropical cyclone motion Statistical-synoptic.
A stepwise multiple regression technique that includes synoptic information together with persistence as predictors.
TYPE
PREDICTORS
PERSISTENCE
PAST 6-, 12-, 24- & 48- HOUR MOTION (DIRECTION & SPEED).
CLIMATOLOGY
DATE, LATITUDE, LONGITUDE, INTENSITY
SYNOPTIC INFORMATION
HEIGHTS & THEIR GRADIENTS, ZONAL & MERIDIONAL WINDS (OBSERVED OR PREDICTED)
FORECAST METHODS WHICH INCLUDE PREDICTED INFORMATION
FROM A NUMERICAL MODEL ARE KNOWN AS STATISTICAL-DYNAMICAL METHODS.

100. MOVEMENT Forecasting Tropical Cyclone Motion Numerical Models.
Solve The Equations Of Motion To Predict The Location Of Max ∂Ζ/∂T

101. FUJIWHARA EFFECT( Sukuhai Fujiwhara)
Sometimes known as Fujiwhara interaction or binary interaction.
Two nearby cyclonic vortices orbit each other and close the distance between the circulations of their corresponding low pressure areas.
Binary interaction of smaller circulations can cause the development of larger cyclone or cause two cyclone to merge into one.

102. ( Sukuhai Fujiwhara) (Contd)
FUJIWHARA EFFECT
( Sukuhai Fujiwhara) (Contd)
Extratropical cyclones tropically engage in binary interaction when within 2000 km of one another.
Tropical cyclonic typically interact when within 1400 km of each other.
Seen in North Atlantic, NE & NW Pacific, SW Indian Ocean & South Pacific Ocean.

103. CONCLUSIONS
Tropical cyclones are basically low pressure areas or closed circulations with warm core systems originating over tropical oceans.
The mean circular wind is of the order of 34 kt or more with relative vorticity being greater than 100x10-06 /sec and pressure deficit at the centre is greater than 15 hPa.

104. CONCLUSIONS
Tropical cyclone formation is most frequent in regions where the sgp, which is the product of six genesis parameters, is maximum. These parameters are:
Low level relative vorticity.
Coriolis parameter.
Inverse of vertical wind shear.
Ocean thermal energy.
Moist stability parameter.
Mid-troposphere relative humidity.

105. CONCLUSIONS
Conditions favorable for formation of tropical cyclone are:
Sea surface temperature greater than 26 deg. Celsius.
Low vertical wind shear.
Easterly waves in the vicinity of ITCZ.
Convectively unstable atmosphere.

106. CONCLUSIONS
The life cycle of a tropical cyclone consists of the following stages:
Formative stage
Immature stage
Mature stage
Decaying stage

107. ?