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Sounding Reference
For what you need a sounding ?
A Sounding ( radiosonde ascent ) returns the state of the atmosphere at a certain point at a certain time . Soundings find particular use in storm prediction. From them can be very easily determine the stability and other relevant parameters for predicting the storm .
The Skew -T Log P representation
This most frequently used graphical representation of a radiosonde ascent is a very quick overview of the current situation. The temperature and the dew point it at a 45 degree angle to the right shown above and the pressure in a logarithmic scale for the Y -axis. Wind speed and wind direction are normally presented as a wind flags on the right edge. Thus one can see the progress of wind speed with height better, I 've attached the wind speed as an additional scale on the x -axis. The wind directions are represented as simple lines right.
Example
Another X - scale is the mixing ratio (mixing ratio) . It is used to determine the condensation level .
Example
Additional scales
In addition to directly measured values (temperature , dew point , wind) , nor CAPE CINH and shows up to a height of 700 hPa graphically. CINH is this multiplied by the factor 5 in order to obtain the graphic representation acceptable levels. (Description of CAPE and CINH see below)
Condensation level
In a Sounding you can choose between two different condensation levels:
Lifting Condensation Level ( LCL)
The LCL is used at the height of the cloud base to determine if the convection is triggered by elevation of fronts or mountains. For this you need the average mixing ratio and the average temperature of the upper air package. As a standard here , the averaged values of the lowest 100 hPa are used. The intersection between the proportions and the Trockenadiabate is the LCL.
Example
Convective Condensation Level ( CCL)
The CCL is used when the convection is triggered Thermal. This is particularly the case with heat lightning . As with the LCL is needed for even the average value of the ratio. The intersection between the proportions and the temperature curve from the measured values of the CCL. The CCL is usually higher than the LCL.
Example
Thunderstorm prediction using a Soundings
Soundings can put in the storm forecast a significant factor; with them to assess the situation accurately and make a statement , above all, what is expected for a type of storm.
As this is only a snapshot of the atmosphere at a certain point, you should never just leave alone the current sounding , but always call the models and pay attention to changes in the next few hours .
The first one looks the best , the curve of the ascending air parcel ( Parcel in ) and compares them to the temperature curve. Parcel , the curve is located far to the left of the temperature curve, the atmosphere is stable and there are not expected thunderstorms. The Lifted Index is a value often used to describe the current stability . A value of> +3.0 ° C in the sounding of 12Z is usually too strong for the formation of thunderstorms. Exception would be a cold front approaching with a strong cooling in the amount or moist air , which flows into the lower atmosphere .
At 00Z rise to pay attention more, because there already may be sufficient alone to sunlight of the coming day to destabilize the atmosphere.
A second factor is to be expected if the storm is moisture in the lower atmosphere . The Lifted index can indeed be negative , but dry air near the ground impossible storm , as one is not tethered cap, which means that rising air packages can not reach the "Level of Free Convection (LFC ) " freely from which to them would arise . Example Cap for a strong thunderstorm .
The third key parameter for storm , raising the standard , it can not determined from a sounding . For this the model maps are consulted.
One sign of improvement can be at most a clockwise rotating wind direction. In the lower atmosphere , it points to warm air advection, which would imply raising .
you want to find out what is expected for a type of thunderstorms , you look on as the first wind profile. no greater increase of the wind is visible to the height, one can assume that will provide only short-lived storm, whose intensity is determined by the instability. With high instability to expect multi-cell , single cells at low instability . Example a multicell Soundings .
If a wind speed reaches at least about 40 knots at 300 hPa, there is the possibility of thunderstorms with a longer life span (Super ) cells. The increase of the wind with height is crucial to create an area separate from the updraft Abwindbereich . For an additional clockwise rotation of the wind with altitude supercells are likely.
The question whether it could be used in conjunction with supercell tornadoes can be as close to answering that the odds are in favor of the largest, if a strong low level jet is present. The low-level jet usually occurs in advance of cold fronts , where large temperature differences develop in the deeper layers of the atmosphere . In Switzerland , the Low -Level Jet its maximum at about 700 hPa (Example). The Jura and the Alps to have a significant impact . In rare cases it happens , however, that the low-level jet has its maximum at about 850 hPa. Then possible combination of supercells and tornadoes (Example).
Sounding parameters
From the measured values a radiosonde ascent can be all sorts of different parameters calculated. They then can the structure of the atmosphere to be assessed more accurately. Further , all parameters are explained in short, to be shown on the right.
850 Wet Bulb Theta -E
Energy in the air at 850 hPa
Sfc - 700 Man Rel Hum
Average humidity between the ground and 700 hPa
Convective Temperature
Exceeding this temperature near the ground , the trigger thermal convection is expected.
Example
Lifted Index
Difference between the rising air package and the ambient temperature measured at a height of 500 hPa
Example
Formula : LI = T500 - T500Parcel
> 0 Thunderstorms unlikely
0 - -2 Thunderstorms possible - trigger needed
-3 - -5 Thunderstorms probable
-5 - -7 Strong / severe thunderstorms . Tornadoes possible
-7 - -9 Move to Alaska
< -9 Yikes
CAPE / CINH
CAPE ( Convective Available Potential Energy ) is the most important size of the storm forecast. It is a direct measure of the energy available for convection . From this one can also calculate the maximum expected updraft speed ( Max Up Vert Vel ) in a thunderstorm.
CINH ( Convective Inhibition ) is the energy that is needed to bring an air pack on the LFC. This can be done by ground-level Erwärnmung or by raising fronts.
Example
<300 Weak convection ( showers)
300-1000 Weak thunderstorms
1000-2500 Moderate thunderstorms
2500-3000 Strong thunderstorms
3000 + Very Strong thunderstorms
Normalized CAPE
This value is approximately the same importance as the Lifted Index, is simply here over the whole range of "Level Of Free Convection ( LFC ) and the "Equilibrium Level ( EL) averaged. CAPE narrow areas which have a large height difference between LFC and El have a small value, while large areas CAPE produce a small difference in height between LFC and EL great values.
Formula: Normalized CAPE = CAPE / ( Height ( EL) - Height ( LFC) ) [m / s ^ 2]
Scale: 00-10 Narrow
10-20 Wide
> 20 Very Broad
Examples: 6:02 m / s ^ 2 (Payerne 02/06/1999 12Z)
6.63 m / s ^ 2 (Payerne 05/08/2003 12Z)
15:12 m / s ^ 2 (Payerne 06/24/2002 00Z )
26.84 m / s ^ 2 (De Bilt 12Z 06/18/2002 )
In Switzerland and Europe , the value of 10 m / s ^ 2 is exceeded only in rare cases.
Max Up Vert Vel
Maximum Aufwärtsgeschwindigkeit in the expected thunderstorms. This does not apply supercells , where the updraft can reach larger values.
Formula: sqrt (2 * CAPE)
850-600 lapse rate
Temperature difference between 850 hPa and 600 hPa is used here for calculating Exp Hail Size.
Wet -Bulb Zero
see External Description ( English). The height of the WBZ is an important prediction of hail size. Is used for calculating Exp Hail Size.
Fawbush -Miller Hail Size
Mean expected hail size in developing storms .
Exp Hail Size
Experimental maximum expected hail size.
Formula
LCL
Height of cloud base in elevation caused by (fronts , mountains) convection.
CCL
Height of cloud base on thermal convection.
LFC
= LFC Level of Free Convection. From this rate is rising , the ascending air parcel without energy from the outside to the EL. The LFC is located at a height where the ascending air parcel , the temperature curve in the direction of cuts warmer. For stable compared Schichting may never . If thermal convection is the LFC = CCL.
Example
EL
EL = equilibrium level. At this altitude, an air parcel reaches the LFC before which has once again exceeded the equilibrium state, ie it increases to go no further. During thunderstorms, the anvil spreads out in this amount.
The EL has nothing to do with the tropopause !
Theta
Value for rising air parcel (not important ).
Theta -E
Value for rising air parcel (not important ).
Mixing Ratio
Value for rising air parcel (not important ).
Showalter Index
Basically the same as the Lifted index with the change that is taken here , the air parcel from 850 hPa. The difference between an ascending air parcel and the ambient temperature is again calculated at 500 hPa. A negative Showalter index exists in all probability a wet base coat , which is an important prerequisite for thunderstorms.
Formula : SI = T500 - T500Parcel
> 4 Thunderstorms unlikely
1-4 Thunderstorms possible - trigger needed
1 - -2 Increasing chance of thunderstorms
-2 - -3 High potential of heavy thunderstorms
-3 - -5 Getting scary
-5 - -10 Extremely unstable
<-10 Head for the storm shelter
K Index
The K Index ( KI ) is composed of a large temperature drop 850-500 hPa and the Grundschichtfeuchte . Dry layers in applied levels (850 hPa and 700 hPa ) can give a false impression.
Formula : KI = ( T850 - T500 ) + TD850 - ( T700 - TD700 )
0-15 No thunderstorms
18-19 Thunderstorms unlikely
20-25 Isolated thunderstorms
26-30 Widely scattered thunderstorms
30-35 Numerous thunderstorms
36-39 Thunderstorms very likely
40 + 100 % chance of thunder storms
Modified Thompson Index
Thompson is the modified index of "Modified K Index " and " Lifted Index. The Modified K comes from the index and referred to the calculation of temperature and dew point for the 850 hPa level to the K index, which does not conform with the measured values here at this altitude, but with the averaged values between the ground and 850 hPa
Formula: TImod = KImod - LI [° C] where KImod = ( TmeanSfc. .850 - T500 ) + TDmeanSfc .. 850 - ( T700 - TD700 )
< = 28 No thunderstorms expected
28-36 Isolated thunderstorms
> 36 Widespread thunderstorms
Total Totals Index
The Total Totals Index ( TTI ) speaks during a wet base layer at the minimum to 850 hPa and below 500 hPa temperature. Both of these are important values for thunderstorm . In a dry interlayer at 850 hPa is the same problem as the K index.
Formula : TT = T850 + TD850 - 2 * T500 ()
<43 Thunderstorms unlikely
43-44 Isolated thunderstorms
45-46 Scattered thunderstorms
47-48 Scattered thunderstorms / isolated severe
49-50 Scattered t-storms/few severe / isolated tornadoes
51-52 Scattered - numerous t-storms/few-scattered severe / isolated tornadoes
53-55 Numerous thunderstorms / scattered tornadoes
56 + You do not want to know
SWEAT index
In the United States successfully angewanter index for the prediction of severe thunderstorms and tornadoes.
Formula: SWEAT = 12 * ( TD850 ) + 20 * ( TTI - 49 ) + 2 * ( WS850 ) + ( WS500 ) + 125 * (sin ( WD500 - WD850 ) + 0.2)
(WAS = wind speed , WD = Winddirection )
< 272 Thunderstorms unlikely
273-299 Slight risk - general thunderstorms
300-400 Moderate risk - approaching severe limits
401-600 Strong risk - few severe tornadoes t-storms/isolated
601-800 High risk of severe tornadoes t-storms/scattered
801 + High wind damage , but not favorable for severe weather
Craven Significant Severe Weather Index
The Craven SigSvr Index is a combined index between CAPE and wind shear between the floor and 6 km altitude.
Formula: Craven SigSvr CAPE = * 0 .6 km Windshear [m ^ 3 / s ^ 3]
Scale: 0-5 Not expected to be severe thunderstorms
50-10 Severe thunderstorms possible
> 10 Severe thunderstorms expected
Examples: 12:24 m ^ 3 / s ^ 3 (Payerne 05/08/2003 12Z)
14:14 m ^ 3 / s ^ 3 (Payerne 02/06/1999 12Z)
33.89 m ^ 3 / s ^ 3 (Payerne 06/24/2002 00Z )
60.49 meters ^ 3 / s ^ 3 (De Bilt 12Z 06/18/2002 )
Supercell Composite Parameter
The SCP is a combined index between the maximum CAPE , 3 km Storm Relative Helicity and Bulk Richardson Windshear . It was developed by the Storm Prediction Center in the U.S.. The larger the value, the higher the probability of supercells and tornadoes.
Formula : SCP = (Most Unstable CAPE / 1000 ) * ( 3km SRH / 100 ) * ( BRN Shear / 40 ) [1 ]
Scale: <= 1 Not expected to supercell
1-4 Supercells are possible
> 4 Super cells are probably
Examples: 1.76 (Payerne 05/08/2003 12Z)
3:19 (De Bilt 12Z 06/18/2002 )
6:12 (Payerne 06/24/2002 00Z )
19:44 (Payerne 02/06/1999 12Z)
Significant Tornado Parameter
The STP is like the SCP from Supercell Composite Parameter of several parts. This CAPE, Lifted Condensation Level height are the (LCL ) above ground (AGL ) , 1km Storm Relative Helicity and 6km Windshear .
Formula : STP = ( CAPE / 1000) * (( 2000 - LCL height AGL ) / 1500 ) * ( 1km SRH / 100) * (0 .6 km Windshear / 20 ) [1 ]
Scale: <= 0.5 Not expected to signifiers (> = F2) tornadoes
> 0.5 Significant tornadoes are also possible
In Switzerland and Europe , the value of 0.5 is achieved only in rare cases, because either the LCL because of low humidity at ground level is too high , or the 1km SRH is too small because of the lack of low-level jets.
Examples: 12:01 (Payerne 05/08/2003 12Z)
12:10 (Payerne 06/24/2002 00Z )
00:25 (Payerne 02/06/1999 12Z)
00:59 (De Bilt 12Z 06/18/2002 )
Experimental Supercell Index for Switzerland ( SIS)
The SIS consists of a combination of maximum wind speed between 850 hPa and 500 hPa and the 100mb Mean Layer CAPE CCL of the lower and middle altitudes (surface - 400 hPa).
Formula : SIS = ( Max Wind Speed 850_500 / 30 * 2 ) * ( CAPE CCL Sfc_400 / 500 ) [J / kg * m / s]
Scale: <1.4 It would not be expected supercell (super Cells not likely).
1.4 - 1.99 Supercells are possible ( Super Cells possible).
> = 2.0 Supercells are expected ( Super Cells expected) .
Graphics:
- Maximum wind speeds 850-500 hPa
- 100mb Mean Layer CAPE CCL (Surface - 400 hPa)
- Experimental Supercell Index for Switzerland ( CH)
KO Index
Relatively new storm Index of the German Weather Service. He describes the potential instability between the lower and upper atmosphere .
Formula : KO - Index = 0.5 * ( + ThetaE700 ThetaE500 ) - 0.5 * ( + ThetaE1000 ThetaE850 )
> 6 Thunderstorms unlikely
2-6 Thunderstorms possible
<2 Severe thunderstorms possible
Index Deep Convective
Index for the prediction of deep convection ( thunderstorms ).
Formula : DCI = T850 + Td850 - SLI
SLI = Surface Lifted Index <10 Thunderstorms unlikely
10-20 Thunderstorms possible
20-30 Strong thunderstorms possible
> 30 Severe thunderstorms possible
CS Index
Thunderstorms and wind shear index CAPE ( see also SWEAT Index ), which was successfully tested in Switzerland in the storm prediction.
SWISS00 / SWISS12 Index
By Heidi Huntrieser specifically for Switzerland ( north of the Alps ) developed thunderstorm indices for the 00Z and 12Z radiosonde ascents.
Storn Direction / Storm Motion
General tensile direction and speed of the train of thunderstorms. Supercell can in some cases significantly deviate !
Example
Shear Wind Dir Sfc - 3000 / Wind Shear Sfc - 3000
Wind Direction and Wind Speed change between the ground and 3000m above ground.
Shear Wind Dir 3000 - 6000 / Wind Shear 3000 - 6000
Wind direction and wind speed change between 3000m and 6000m on the floor above ground.
Shear Wind Dir Sfc - 6000 / Wind Shear Sfc - 6000
Wind direction and wind speed change between the ground and 6000m above ground.
Bulk Shear
Is used for bulk Richardson Number ( important).
Ri Shear
Is used for bulk Richardson Number ( important).
Bulk Richardson Number
From the Bulk Richardson Number ( BRN) can be concluded that what is expected for a Gewittertyp ( see also Energy Helicity Index).
Formula: BRN = ( CAPE / 0- 6km Shear )
<10 Thunderstorms unlikely - single cell type
11-49 Moderate chance - supercell in nature
50 + Strong chance - multi cell type
Storm Relative Helicity
The Storm Relative Helicity (SRH ) is a measure of the change of direction and speed of the wind in the lower 3000m.
Example
<80 unlikely Super Cells
80-150 Supercell Storms
150-299 F0 , F1 Tornadoes
300-499 F2 , F3 Tornadoes
> 450 F4 , F5 Tornadoes
Effective Storm Relative Helicity
The Effective SRH should describe more precisely for a thunderstorm available Helicity than the conventional SRH . The Effective SRH is not necessarily between the ground and 3 km altitude calculated , but between the X point where the ascending air parcel , for the first time at least 50 J / kg and reaches X + 3km. Especially with the Soundings in the night where a soil inversion , the value is different from the normal SRH . During the day, both values are generally identical , except the post-frontal area where it is often elevated CAPE .
Energy Helicity Index
The Energy Helicity Index ( EHI ) is needed in the U.S. as one of the best indices to predict tornadoes. It is calculated from CAPE and Storm Relative Helicity , so the two most important parameters for the determination of the expected storm type.
Formula : EHI = ( CAPE * SRH ) / 160,000 < 0.8 Tornadoes unlikely
0.8-1 F0 , F1 Tornadoes
1-4 F2 , F3 Tornadoes
> 4 F4 , F5 Tornadoes