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Transcript of SIGMET Analysis
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Executions and Techniques onSIGMET Consulting Information
April, 2011 Beijing
Qiang Xuemin
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Main topic
To briefly introduce the executions
and techniques on SIGMET information
which have been successfully applied inaeronautic significant weather forecasts .
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Data used in this work:
Conventional telegram report
Output products from the globalmid-term numerical weatherforecast model
Satellite data
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4 Phenomenaof SIGMETConsultingInformation
Contents
Thunderstorm
Aircraft Bumps
Aircraft Icing
SevereLee Waves
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Executions and Techniques onThunder Storm1 Diagnostics on stabilization index of the
atmosphere
Multi-factor-overlapping techniques on
thunder storm area
Classification and extrapolation of satellite
data for convective weather
Integrated forecast techniques on thunder
storm area
Thunder
Storm
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Active convections is in favor of a thunder storm.
favorable conditions
I. conditionally unstable stratification in the atmosphere
II. abundant in water vapor
III. a kind of dynamic trigger mechanism
Characteristics
meso-scale system / short lifetime / strong convective weather
Forecast
Yes or No before 0-6 hours
About Thunder Storm
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1-1 Diagnostics on stabilization index of the atmosphere
Potential Forecast
for
Convective Weather
Diagnostics
Thresholdfor these index
Index characterizing instability of the atmosphere
Outputproducts from NWF
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1
2
3
4 4. Energy Index
1. Thermal Index
2. Humidity
Index
3. Dynamical
Index
Diagnosticson stabilizationindex of the atmosphere
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1 Thermal Index
A---index
Air mass index---K
Potential instability index---I
Showalter Index---SI
Simplified Showalter Index---SSI
Yamazaki index---KYI
Bejerknese Index---BI
Diagnostic on convective instability
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A---index
)(500
85 0
500850 dttttA
---- to describe the vertical humidity condition in the whole
volume
t500 / t850 : temperatue at 500 / 850 hPa
td : dew-point
When A 0, probability of a thunderstrom is 90%
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1 Thermal Index
A---index
Air mass index---K
Potential instability index---I
Showalter Index---SI
Simplified Showalter Index---SSI
Yamazaki index---KYI
Bejerknese Index---BI
Diagnostic on convective instability
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Air mass index---K
K t t t t td d 850 500 850 700( )or
500700850850 )()(2 TTTTTTK dd
---- the bigger the K index is, the more unstable in the air will be.
K 20oC, no thunderstorm20oCK25oC, single thunderstorm25oC K30oC, sporadic thunderstorms30o C K35o C, scattered thunderstorms35o C K , massive thunderstorms
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1 Thermal Index
A---index
Air mass index---K
Potential instability index---I
Showalter Index---SI
Simplified Showalter Index---SSI
Yamazaki index---KYI
Bejerknese Index---BI
Diagnostic on convective instability
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Potential instability index---I
700
700925200
925300 01.02
dthhh
hhI
h : geopential height
---- favorable condition : colder in the upper air, warmer in lower
---- the bigger I index is, the more instable of the stratification will be
K 2.79, no thunderstorm
K2.79, yes
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1 Thermal Index
A---index
Air mass index---K
Potential instability index---I
Showalter Index---SI
Simplified Showalter Index---SSI
Yamazaki index---KYI
Bejerknese Index---BI
Diagnostic on convective instability
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Showalter Index---SI
500 SSI T T ----temperature difference between the stratification curve and the statecurve, describing air mass at 850hPa rising along dry-adiabatic curve
till to the condensation level then rising along wet-adiabatic curve till
to 500hPa (with temperature Ts). T500 is the environmental
temperature at 500hPa.
---- positive: rising air mass with high temperature
negative: with low temperature
Value of SI Index Possibility of thunderstorm event
3
o
Clittle or not
3oCSI0oC Shower be possible
0oCSI-3oC Thunderstorm be possible
-3oCSI-6oC Strong thunderstorm be possible
-6oCSI Severe convective weather be possible
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1 Thermal Index
A---index
Air mass index---K
Potential instability index---I
Showalter Index---SI
Simplified Showalter Index---SSI
Yamazaki index---KYI
Bjerknes Index---BI
Diagnostic on convective instability
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Simplified Showalter Index---SSI
'
500 STTSSI ---- Ts
: air mass at 850hPa rising along dry-adiabatic curve till to
500hPa (with temperature Ts). T500 is the environmental
temperature at 500hPa.
---- usually, SSI 0.
---- The smaller the SSI is, the stable the air would be.
---- SSI has outstanding exhibition in forecasting strong convective
weather, such as tornadoes, hailstones, and so on
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1 Thermal Index
A---index
Air mass index---K
Potential instability index---I
Showalter Index---SI
Simplified Showalter Index---SSI
Yamazaki index---KYI
Bjerknes Index---BI
Diagnostic on convective instability
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Yamazaki index---KYI
KYIT S
T T
A
d
( )850
humidity condition at low level
stabilization of the air
temperature advection
at 500hpa While: =1, =1105s0 (statistically)S -----(T-Td)850 ----- ( units)T ----- 10-5s-1
8501 ( )
0{A
A
d
A
T ST S
T T
T SKYI
1
2
3
KYI
pay attention
possibility is high
in all likelihood
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1 Thermal Index
A---index
Air mass index---K
Potential instability index---I
Showalter Index---SI
Simplified Showalter Index---SSI
Yamazaki index---KYI
Bjerknes Index---BI
Diagnostic on convective instability
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Bjerknes Index---BI
200 TZBI
Z: thickness from 1000-700hPa (unit: gpm)
T: temperature at 700hPa (unit: K)200: empirical coefficient
BI 94, a thunderstorm might occur.
When BI is used in a frontal circumstance, the correct rate
would be more than 81%.
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1 Thermal Index
A---index
Air mass index---K
Potential instability index---I
Showalter Index---SI
Simplified Showalter Index---SSI
Yamazaki index---KYI
Bjerknes Index---BI
Diagnostic on convective instability
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Diagnostic on convective instability
0
0
0
se
p
stable
neutral or
instable
0
0
0
se
z
stable
neutral
instable
se: pseudo-equivalent potential temperature
This method usually is used in diagnosing weather systems with
systematical updraft flows.
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1
2
3
4 4. Energy Index
1. Thermal Index
2. Humidity
Index
3. Dynamical
Index
Diagnosticson stabilizationindex of the atmosphere
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2 Humidity Index
difference between air temperature and dew-point temperature
divergence of the water vapor flux
dTTTTD
simple, but useful
When TTd=0 saturated.
Based on the NWF products, we can get TTD at each grid points.
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2 Humidity Index
difference between air temperature and dew-point temperature
divergence of the water vapor flux
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divergence of the water vapor flux
Water vapor flux, depicting the strength and direction of thetransportation of the moisture.
FH: flux on horizontal
FZ: flux on vertical
horizontal wind speed vertical speed
specific humidity density of the air
HF V q g
qFz
V
q
( ) ( ) ( )V q g uq g vq g x y
positive: outcome or lost of the water vapor
negative: income or convergence of the water vapor
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1
2
3
4 4. Energy Index
1. Thermal Index
2. Humidity
Index
3. Dynamical
Index
Diagnosticson stabilizationindex of the atmosphere
Dynamical Index
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Dynamical Index3
vorticity
divergence
vertical velocity
yu
xvV
D Vu
x
v
y
unit: 10-6s-1
unit: 10-5s-1
752
1
925925 D
unit: 10-3hPas-1
at 925hPa
PDDkkkk
)(
21
11k level
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1
2
3
4 4. Energy Index
1. Thermal Index
2. Humidity
Index
3. Dynamical
Index
Diagnosticson stabilizationindex of the atmosphere
Energy Index
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Energy Index4
convective available potential energy CAPE
modified CAPE MCAPE
normalized CAPE NCAPE
downdraft CAPE DCAPE
convective inhibitation CIN
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convective available potential energyCAPE
( )EL
LFC
Zvp ve
veZ
T TCAPE g dZ
T
Tv pseudo temperature
subscript mark
e ---- environment air
p --- air parcel
LFC level of free convectionLCL level of condensation
EL equilibrium level
EAL equivalent area level
dry adiabatic curve
wet adiabatic curve
state curve
stratification curve
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convective available potential energyCAPE
Two aspects noticeable in computing CAPE
corrections for Tv)1(
1
/1rT
r
rTT
v
height of LCLsurface / h850 / h925 /
height with the biggest wet-bulb temperature from 1000 to800hPa
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modified CAPE MCAPE
---- re and ri stand for the mixing ratio of water vapor in
liquid and solid state, respectively.
---- g (re + ri ) stands for the dragging function caused by
the water component in the air
[ ( ) ]EL
LFC
Z
e i pZ
Tvp TveMCAPE g r r dZ
Tve
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normalized CAPE NCAPE
FCL EL LFC
CAPE CAPE CAPE
H Z Z
----designed to consider the effect on the vertical velocity
caused by the vertical distribution of the floating force
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downdraft CAPE DCAPE
In the body of a storm, when precipitation, ice water or crystalvaporizes in the unsaturated air or melts at the frozen layer, downdraft
occurs.
( ) ln
1 ( )
n
i
i
n
p
d e pp
Z
ve vpZ
ve
DCAPE R T T d p
g T T dZT
---- Pi / Zi pressure or height where downdraft begins
---- Pn / Zn pressure or height when downdraft reaches the ground
Approximatively, the maximum down speed can be written as:
max 2W DCAPE
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convective inhibition CIN
dry adiabatic curve
wet adiabatic curve
state curve
stratification curve
LFC
i
Z e p
ZB
T TCIN g dz
T
TB mean temperature at ABL
(atmospheric boundary layer)
subscript mark
e ---- environment air
p --- air parcel
ZLFC level of free convection
Zi original level2
CINW CIN
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Executions and Techniques on Thunder Storm1
Diagnostics on stabilization index of
the atmosphere
Multi-factor-overlapping techniqueson thunder storm area
Classification and extrapolation of
satellite data for convective weather
Integrated forecast techniques on
thunder storm area
Thunder
Storm
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1-2 Multi-factor-overlapping method on thunderstorm area
=0
=0
trough
SW airflow
chart for multi-factor-overlapping method
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indices selection
stability indices
0se
p
K>35
SI0
KYI1
BI94
TI>0
I2.79
water vapor indices850 850
2.0d
T T
850( ) 0qV
850 850 925 925( ) ( ) 5.0d dT T T T
850 700( ) ( ) 0qV qV
momentum indices
and
or
700 5000W W
850( ) 0V
5000V
850 700( ) ( ) 0V V and
energy indices CAPE>200
convective precipitation RC>3mm
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Multi-factor-overlapping method in forecast thunderstorm
Step-wise
decreasing FAR
Executions of
indices
overlapping
Integrated
judgment on
severe weather
850 850 925 925( ) ( ) 25d dT T T T
15K
500 700 850 92530
se se se se K
To judge whether 15
indices meet the
requirements or not. If it
is true, NP+1.
If NP>8 and CAPE>800
Or NP>11
Or CAPE>2000
Or Rc>5mm
Then there will be a thunderstorm
within the forecast area.
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Executions and Techniques on Thunder Storm1
Diagnostics on stabilization index of
the atmosphere
Multi-factor-overlapping techniqueson thunder storm area
Classification and extrapolation of
satellite data for convective weather
Integrated forecast techniques on
thunder storm area
Thunder
Storm
1-3 classification and extrapolation of satellite data for convective
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1 3 classification and extrapolation of satellite data for convective
weather
including:
quality control on Satellite data
classification and extraction ofconvectivecloud,jet stream cloud, frontal cloud and
cloud systems related with Lee waves
obtaining live information ofsandstorm
1-3 Identification and extrapolation of satellite data for convective
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1 3 Identification and extrapolation of satellite data for convective
weather
threshold technique
space correlation technique
bi-channel dynamic threshold technique
dynamic clustering technique
brightness temperature technique
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Executions and Techniques on Thunder Storm1
Diagnostics on stabilization index of
the atmosphere
Multi-factor-overlapping techniqueson thunder storm area
Identification and extrapolation of
satellite data for convective weather
Integrated forecasting techniques on
thunder storm areas
Thunder
Storm
1 4 I t t d f t t h i th d t
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1-4 Integrated forecast techniques on thunder storm area
Regression integrated technique is used to forecast thethunder storm rainfall area.
Basic principle:
n
i
iiYbbY
1
0
b0 mean of the forecast objective
bi coefficient, reflecting the relationship between forecasts(actually, they represents the variety forecast measures)
1 4 I t t d f t t h i th d t
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Steps:
a variety methods forecasting thunderstorms are used tocompute inversely the history samples
Use MOS method, output of the forecasts are treated as differentfactors
Set up a forecast model by using the regressive integratedtechnique
Substitute results of the various methods to the model and drawthe final forecast conclusion.
1-4 Integrated forecast techniques on thunder storm area
C t t
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4 Phenomenaof SIGMETConsultingInformation
Contents
Thunderstorm
Aircraft Bumps
Aircraft Icing
Severe Lee Wave
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Executions and Techniques onAircraft Bumps2
2 1 Aircraft Bumps and The Turbulences
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Bumping is a kind of phenomenon that a flying aircraft goes up and
down and sways from the right to the left badly, or its body
shakes violently. It is caused mainly by the turbulences in the
atmosphere.
Category of the Turbulences:
Dynamical Turbulences
Thermal Turbulences
Wind Shear Turbulences
Wake Vortex Turbulences
2-1 Aircraft Bumps and The Turbulences
2 2 Mechanism of the Turbulences:
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2-2 Mechanism of the Turbulences:
G
Yn
SG
VKWn
2
g
a
mg
ma
G
Yn
VSKWY 2
1
Loading coefficient
Y ascending force
G gravity
a acceleration
W vertical wind speed of the gust
density of the air
V speed of the aircraft
K coefficient of slope
S area of the airfoil
n increment of n
2 3 Di d F t Ai ft B
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2-3 Diagnose and Forecast on Aircraft Bumps
Richardson Index
Ellrod Index
Ti Index
E Index
L Index
Integrated Diagnose
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Richardson Index---a classical method
2( / )( / ) /Ri g z v z
static stability of the layer vertical sheer of the layerThe index operates well in two circumstances:
areas closing to a jet stream
areas with gales near the ground surface and
unstable air at the bottom
A Vertical section of Ri is helpful in figuring out the layer on
which the aircraft bumps might take place.
2 3 Di d F t Ai ft B
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2-3 Diagnose and Forecast on Aircraft Bumps
Richardson Index
Ellrod Index
Ti Index
E Index
L Index
Integrated Diagnose
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Ellrod Index
In Practical,
[ ]TI VWS DEF CVG
21
22
y
u
x
v
y
v
x
uDEF
y
v
x
uCVG
z
VVWS
negative of divergence
wind shear on vertical direction
flow field deformation made
by stretch in horizontal and
shear in vertical
TI VWS DEF unit: 10-7s-2
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Degree of bump Value of TI
light TI4
Light-medium 4
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Ti Index----applied in NMC, U.S.A
V
The bigger Ti index is, the stronger the bumps will be.
Ti >5.1 a medium Bump might occurs.
Ti
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2-3 Diagnose and Forecast on Aircraft Bumps
Richardson Index
Ellrod Index
Ti Index
E Index
L Index
Integrated Diagnose
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E Index----Dutton (1989)
v
h wind shear in horizontal
unit: m/s/100Kmwind shear in vertical
unit: m/s/1000Km
21.25 0.25 10.5
h vE
E 5 7.5 10 15 20 25 30
P(%) 0.0 0.95 1.55 2.2 2.8 4.2 7.5
Table3 relationship between E index and the probability of a
medium CAT in 100Km-averaged flight test
2-3 Diagnose and Forecast on Aircraft Bumps
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2-3 Diagnose and Forecast on Aircraft Bumps
Richardson Index
Ellrod Index
Ti Index
E Index
L Index
Integrated Diagnose
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L Index method----a probability method
wind shear in horizontal unit: m/s/100Km
wind shear in vertical unit: m/s/1000Km
52.2133.0718.0268.7
n
u
n
T
z
uL
Step 1 compute L index
22
z
v
z
u
z
u
22
y
v
x
u
n
u
22
yT
xT
nT temperature shear in horizontal unit: /s/100Km
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L Index method----a probability method
Step 2 get the probability------P
Lep
59.01
1
generally,
86%>P75% light CAT forecast output --- 1
95%>P86% moderate CAT forecast output --- 2
P96% svevere CAT forecast output --- 3
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integrated diagnose on CAT areas
5
1 1 2 2 3 3 4 4 5 5
1
i i
i
F k f k f k f k f k f k f
ki weightfi output for 5 forecasts
Contents
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4 Phenomenaof SIGMETConsultingInformation
Contents
Thunderstorm
Aircraft Bumps
Aircraft Icing
SevereLee Wave
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Executions and Techniques onAircraft Icing3
3-1 Aircraft Icing
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3 1 Aircraft Icing
3-1 Aircraft Icing
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3 1 Aircraft Icing
3-2 Factors affecting Aircraft Icing
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3 2 Factors affecting Aircraft Icing
I weather conditionstemperature ----- TAT (total air temperature)
LWC and the scales of the water droplets
cloud phase state
II flight parameters
including flight speed, aircraft shape and type and other
parameters
3-3 Arithmetic on Aircraft Icing
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3 3 Arithmetic on Aircraft Icing
3-3-1 Icing computation scheme 1
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3 3 c g co putat o sc e e
step1. computations on LWC
)87.2/()(95.0 hhchc TQQPL ( for cumulous cloud )
))36(/()(1025.0 24 TTTTEfLhcn ( for stratus cloud )
quantities at the flight level tk: temperature()Ph : pressure f: relative humidity Th: temperature (K)
Qh: saturated specific humidity
quantities at the cloud bottom
Tc: temperature Qc: saturated specific humidity
)5.237/(5.7
1011.6hhtt
E
2
hc TTT
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value L0.01 0.01
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step2. diameter of moderate cloud droplet
cloud St Sc Ns As Ac Cu Cb
DMV 20 28 48 16 18 22 36
Table 5 diameters of moderate water droplets for different clouds
DMV 1 17 28 50 >50
rank D1 D2 D3 D4 D5
unit: m
Table 6 classification for Dmv
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step3. classification for environmental temperature
value T>0 -5
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step4. index matrix for severe icing I index
T1: T>0, I=0
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T2-5
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T3-10
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T4-20
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T5T-20
I D1 D2 D3 D4 D5
L1 0 0 0 0 5
L2 0 1 2 3 6
L3 0 2 2 3 7
L4 0 3 3 4 8
L5 0 5 5 6 9
L6 0 7 7 7 10
3-3-2 Icing computation scheme 2
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criterions on Icing
-8
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rank for Icing:
0-no icing
1-trace rime icingTRC-RIM2-light mixed icingLGT-MXD3-light rime icingLGT-RIM4-light clear icingLGT-CLR5-modetate mixed icingMDT-MXD6-moderate rime icingMDT-RIM7-moderate clear icingMDT-CLR
Define T-Td=ddp
Table 9 RAOB Icing Project
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wet layer temperaturet
-8
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Rap Icing Project ( Forbs and Thompson, 1986 )
(1) stratum icing
-12
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VV Index ( Wang Xinwei, 2002)
10/)]49/()14([]2)50[( TTRHII
RH: relative humidity T: temperature
4 > I I 0 and -0.2pa/s light icing VV=1
7 > I I 4 and -0.2pa/s moderate icing VV=2
I I 7 and -0.2pa/s severe icing VV=3
Final criterions:
3-3-4 integrated icing forecast
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icing area
rank of icing
5 indicesintegration of overlapping technique
weighted averaging method
0 1 2 3
none light moderate severe
Contents
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4 Phenomenaof SIGMETConsultingInformation
Thunderstorm
Aircraft Bumps
Aircraft Icing
SevereLee Waves
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Executions and Techniques onSevere Lee Waves4
4
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Executions and Techniques onSevere Lee Waves4
wave length 1.8 ~ 70Km, most is in the range of 5~20Km. Changeswith the height and the wind speed.
amplitude several hundred meters ~ 2Km. Most is 0.3~0.5Km.
vertical speed 2~6 ms-1
Properties The taking place of Lee Waves depends on two terms:
static stability of the air
wind speed
4-1 Scorer Parameter Used in Lee Waves Theory
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2
2
2
21
zu
uugl
( Scorer, 1949 )
u wind speed upright to the mountain ridge
T environmental temperature
g gravity acceleration
d adiabatic vertical temperature descending rate of
dry air
vertical temperature descending rate of theenvironment
1 ( )T
4-1 Scorer Parameter Used in Lee Waves Theory
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2
2
2
21
zu
uugl
( Scorer, 1949 )
2
2
gl
u
When there is wave fluctuations at the lee ofthe mountain, l2 is certain to decrease with the
height. As the wind speed always increases
with height and the stratification is stable or
increases only a little, l2 at upper levels usually
are smaller than that at lower levels. The
smaller l2 is changed with the height, the
possibility of Lee waves is larger.
4-2 arithmetic 2 in forecasting Lee Waves
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favorable situation for Lee waves:
stable stratification
stability at low level larger than at high level
wind direction at low level consistent with that at high level---no inversion
2 lnN gz
20N
layer with N
2
descending
below 500hPa
consistency in winddirection at low and high
vertical section of wind
speed
X
Y
Z
apparent wave fluctuations
with wave length of 10-70Km
maximum vertical speed at
mid-level, small vertical speed
at low and high
Lee
Waves
4-3 integration in forecasting Lee Waves
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As the approaches introduced previously,the integrated multi-index-overlapping
techniques will also be applied in the forecast of
the severe mountain Lee Waves areas.
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Thanks for your attention!