CN103809220A - Low-level wind determining method - Google Patents

Abstract

The invention belongs to the technical field of atmospheric sciences and discloses a low-level wind determining method. The low-level wind determining method includes: laying low-level wind fields according to observation data characteristics through statistically analyzing low-level wind data provided by different observation stations, using an interpolation method for the layer lack of the low-level wind observation value to obtain the unmeasured data; when the layers of the low-level wind observation values of different observation stations are overlapped, correcting the low-level wind data of the overlapped layers, building continuous wind fields, and using a regression method to construct a low-level wind computing equation to obtain the low-level wind data. The low-level wind determining method guarantees the low-level wind solving accuracy and provides the technical support for the return of manned spacecrafts and other space flight and aviation activities.

Description

A kind of low latitude wind is determined method

Technical field

The invention belongs to meteorological technical field, relate to a kind of low latitude wind and determine method.

Background technology

Indication of the present invention low latitude wind is the wind of 10m～3000m scope, and because low latitude wind is to manned spaceship flight path, and the track of the low flyer such as retrievable satellite, guided missile, aircraft has material impact, is the crucial meteorological element of precise orbit determination and orbit prediction.

At present in the space mission such as launching site, landing field place, and the meteorological site such as airport all has anemometer tower and wind profile radar, is two kinds of major equipments surveying low latitude wind, but that two kinds of equipment is surveyed height, precision, data density etc. is all not identical.Wind field below anemometer tower measuring distance ground 100m, the height of measurement is totally 5 layers of 10m, 25m, 50m, 75m, 100m, its measuring accuracy 0.1m/s, density measurement is 1 minute; The wind field of the detectable 80m～3253m of wind profile radar, the vertical demixing of detection is no less than 25 layers, and measuring accuracy is 1m/s, and density measurement is 15 minutes; Two kinds of data only exist and overlap in vertical height near 100m.Therefore, low latitude wind ensure in, how to fully utilize these two kinds of allos data calculate low latitude wind be one calculate a difficult problem.For example, in the manned astro-engineering, calculate airship track, track while especially returning need to provide accurate low latitude wind vector data, low latitude wind vector comprises low latitude wind wind direction and wind speed.Thus, propose how to mate anemometer tower and wind profile radar data, calculated the problem of low latitude wind vector.

In low latitude wind vector is in the past calculated, routine is to utilize linear interpolation method, take anemometer tower and wind profile radar detection information as data basis, the low latitude wind below 100m is utilized anemometer tower data, utilizes Wind Profiler Data to carry out linear interpolation to low latitude wind more than 100m to calculate.Because the detection height of wind profile radar is also non-constant, it is more that data lack survey, adopts linear interpolation method to calculate will cause obvious error for the wind vector of a certain height; Especially when in the time that two kinds of detection datas of 100m height exist bigger difference, be difficult to provide low latitude wind result of calculation accurately.

Summary of the invention

The object of the present invention is to provide one low latitude wind computing method accurately, determine and forecast precision with the flight path that improves the low flyers such as manned spaceship.

For achieving the above object, low latitude provided by the invention wind computing method comprise the following steps:

Step 1, set up continuous altitude wind field

The low latitude wind data that the different research stations of statistical study provide, carries out layering by observation data feature to altitude wind field, adopts interpolation method to solve the scarce data of surveying to the layer of disappearance low latitude wind observed reading.During for the ply of low latitude, different research station wind observed reading, the low latitude wind data of overlapping layer is corrected to coupling.Specific as follows:

1.1, altitude wind field layering

The low latitude wind data that the different research stations of statistical study provide, carries out layering by observation data feature to altitude wind field.Layering number is directly proportional to density and the precision of observation data, and highly lower, layering is closeer.

1.2, adopt interpolation method to solve and lack the scarce survey data of surveying layer

Survey the low latitude wind observed reading of layer height apart from two height of its difference in height minimum according to lacking, adopt interpolation method to solve and lack the scarce survey data of surveying layer, specific as follows:

If lay respectively at and lack below and the top of surveying layer height, the scarce survey low latitude wind speed degree V of this layer apart from the low latitude wind observed reading that lacks two height surveying the poor minimum of layer height _s0with wind direction V _x0as follows respectively:

$V_{s0}=V_{s1}+\frac{V_{s2}-V_{s1}}{Z_2-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HSA0000101474460000012.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}\&times;(Z_0-Z_1)$

$V_{x0}=V_{x1}+\frac{V_{x2}-V_{x1}}{Z_2-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HSA0000101474460000012.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}\&times;(Z_0-Z_1)$

If be all positioned at and lack the below of surveying layer height, the scarce survey low latitude wind speed degree V of this layer apart from the low latitude wind observed reading that lacks two height surveying the poor minimum of layer height _s0with wind direction V _x0as follows respectively:

$V_{s0}=V_{s1}-\frac{V_{s2}-V_{s1}}{Z_2-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HSA0000101474460000012.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}\&times;(Z_1-Z_0)$

$V_{x0}=V_{x1}-\frac{V_{x2}-V_{x1}}{Z_2-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HSA0000101474460000012.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}\&times;(Z_1-Z_0)$

If be all positioned at and lack the top of surveying layer height, the scarce survey low latitude wind speed degree V of this layer apart from the low latitude wind observed reading that lacks two height surveying the poor minimum of layer height _s0with wind direction V _x0as follows respectively:

$V_{s0}=V_{s1}+\frac{V_{s1}-V_{s2}}{Z_1-{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HSA0000101474460000012.png,HSA0000101474460000022.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2}\&times;(Z_0-Z_1)$

$V_{x0}=V_{x1}+\frac{V_{x1}-V_{x2}}{Z_1-{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HSA0000101474460000012.png,HSA0000101474460000022.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2}\&times;(Z_0-Z_1)$

Wherein, V _s1, V _s2be respectively apart from the low latitude wind speed that lacks two height surveying the poor minimum of layer height, Z ₁, Z ₂be respectively two height surveying the poor minimum of layer height apart from lacking, Z ₀for surveying layer height apart from lacking; V _x1, V _x2be respectively apart from the low latitude wind direction that lacks two height surveying the poor minimum of layer height.

1.3, obtain the overlapping layer low latitude wind wind speed and direction of low latitude, different research station wind observed reading

Overlapping layer to low latitude, different research station wind observed reading carries out low latitude wind data correction, obtains the overlapping layer low latitude wind wind speed and direction of low latitude, different research station wind observed reading.

Overlapping layer low latitude wind correction wind coupling to low latitude, different research station wind observed reading is as follows:

Wherein, V _{v orders}for ordering the overlapping layer low latitude wind wind speed after distance coupling, V _{v surveys}for the measured value of the lower low latitude wind wind speed of precision,

what be low latitude, different research station wind wind speed at the long-term mean value of overlapping layer height is poor,

low latitude wind wind speed that precision the is lower long-term mean value at overlapping layer height,

low latitude wind wind speed that precision the is higher long-term mean value at overlapping layer height.

The overlapping layer low latitude wind wind direction of low latitude, different research station wind observed reading is corrected to coupling as follows:

Wherein, V _{d orders}correct the overlapping layer low latitude wind wind direction after coupling, V _{d surveys}for the measured value of the lower low latitude wind wind direction of precision, what be low latitude, different research station wind wind direction at the long-term mean value of overlapping layer height is poor,

low latitude wind wind direction that precision the is lower long-term mean value at overlapping layer height,

low latitude wind wind direction that precision the is higher long-term mean value at overlapping layer height.

Step 2, solve low latitude wind

According to the altitude wind field of setting up, the error between low latitude wind calculated value and the measured value of each layer, through deviation statistics analysis, sets up regression equation and solves low latitude wind.

Solve low latitude wind wind direction

with wind speed specific as follows:

$\widehat{y_d}=a_0+a_1{V}_d$

${\hat{y}}_v=b_0+b_1{V}_v+b_2{V_v}^2$

Wherein,

for the low latitude wind wind direction value solving, V _dfor the low latitude wind wind direction value of equivalent layer in the continuous altitude wind field of step 1 foundation, a ₀, a ₁for one-variable linear regression equation regression coefficient, a ₀with a ₁according to the conception of history measured value of the low latitude wind wind direction of equivalent layer and its corresponding historical calculated value, utilize least square method to determine;

for the low latitude wind air speed value solving, V _vfor the low latitude wind air speed value of equivalent layer in the continuous altitude wind field of step 1 foundation, b ₀, b ₁, b ₂for regression equation regression coefficient, b ₀, b ₁, b ₂according to the conception of history measured value of the low latitude wind wind speed of equivalent layer and its corresponding historical calculated value, utilize least square method to determine.

The useful technique effect of the present invention:

The low latitude wind data that the present invention provides according to different research stations, sets up continuous low latitude wind wind field, and adopts homing method to determine the equation that solves low latitude wind.Reach and fully utilized various detection height, frequency, density, the precision low latitude wind data that all not identical different research stations provide, guaranteed low latitude wind solving precision.The inventive method is returned at manned spaceship, have significant application value in guided missile, aircraft etc. low flyer precise orbit determination.Return to drop point at China's manned spaceship and determine etc. in great solar-system operation, the invention provides important technical support.

Accompanying drawing explanation

Fig. 1 is that low latitude of the present invention wind is determined method flow diagram.00:00:31-03:30:33, under: 18:45:27-23:15:35

Fig. 2 is to be the low latitude wind detection data two dimension wind field figure of 00:00:31-03:30:33 the time period.

Fig. 3 is to be the two-dimentional wind field figure after employing the present invention of 00:00:31-03:30:33 fills a vacancy to low latitude wind detection data the time period.

Fig. 4 is to be the low latitude wind detection data two dimension wind field figure of 18:45:27-23:15:35 the time period.

Fig. 5 is to be to be to be the two-dimentional wind field figure after employing the present invention of 18:45:27-23:15:35 fills a vacancy to low latitude wind detection data the time period time period.

Fig. 6 is the low latitude wind that adopts the present invention to calculate and the low latitude wind accuracy comparison figure that adopts linear interpolation method to calculate.

Embodiment

Below in conjunction with accompanying drawing, be defined as example with a manned space flight task return trajectory, the present invention is described further.As shown in Figure 1, low latitude of the present invention wind is determined method, comprises the steps:

Step 1, set up continuous altitude wind field

The low latitude wind data that the different research stations of statistical study provide, carries out layering by observation data feature to altitude wind field, adopts interpolation method to solve the scarce data of surveying to the layer of disappearance low latitude wind observed reading.During for the ply of low latitude, different research station wind observed reading, the low latitude wind data of overlapping layer is revised.Specific as follows:

1.1, altitude wind field layering

The low latitude wind data that the different research stations of statistical study provide, carries out layering by observation data feature to altitude wind field.Layering number is directly proportional to density and the precision of observation data, and highly lower, layering is closeer.

For example: the low latitude wind data of comparative analysis anemometer tower and wind profile radar observation

Anemometer tower is surveyed 10m, 25m, 50m, 75m, the 100m wind field of totally 5 layers, its measuring accuracy 0.1m/s, and density measurement is 1 minute; Wind profile radar is surveyed the wind field of inverting 80m～3253m, and its vertical demixing is no less than 25 layers, and measuring accuracy is 1m/s, and density measurement is 15 minutes; Two kinds of data only exist overlapping near 100m height.The precision of anemometer tower data, density, continuity, stability are all better than Wind Profiler Data.According to density measurement, data precision, and the demand calculated of Manned Spacecraft Return, the low latitude wind below 3000m is carried out to layering, be divided into 20 layers, wherein 100m is following surveys and is highly divided into 10m, 25m, 50m, 75m, 100m 5 layers by anemometer tower; 100m～300m interval 50m, is divided into 4 layers (150m, 200m, 250m, 300m); 300m～1000m vertical separation 100m, is divided into 7 layers (400m, 500m, 600m, 700m, 800m, 900m, 1000m); 1000m～3000m vertical separation 500m, is divided into 4 layers (1500m, 2000m, 2500m, 3000m).By layering, can obtain the basic low latitude wind data of each height.

1.2, adopt interpolation method to solve and lack the scarce survey data of surveying layer

Survey the low latitude wind observed reading of layer height apart from two height of its difference in height minimum according to lacking, adopt interpolation method to solve and lack the scarce survey data of surveying layer, specific as follows:

If lay respectively at and lack below and the top of surveying layer height, the scarce survey low latitude wind speed degree V of this layer apart from the low latitude wind observed reading that lacks two height surveying the poor minimum of layer height _s0with wind direction V _x0as follows respectively:

$V_{s0}=V_{s1}+\frac{V_{s2}-V_{s1}}{Z_2-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HSA0000101474460000012.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}\&times;(Z_0-Z_1)$

$V_{x0}=V_{x1}+\frac{V_{x2}-V_{x1}}{Z_2-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HSA0000101474460000012.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}\&times;(Z_0-Z_1)$

If be all positioned at and lack the below of surveying layer height, the scarce survey low latitude wind speed degree V of this layer apart from the low latitude wind observed reading that lacks two height surveying the poor minimum of layer height _s0with wind direction V _x0as follows respectively:

$V_{s0}=V_{s1}-\frac{V_{s2}-V_{s1}}{Z_2-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HSA0000101474460000012.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}\&times;(Z_1-Z_0)$

$V_{x0}=V_{x1}-\frac{V_{x2}-V_{x1}}{Z_2-{\mathrm{<figure-callout\; id="1"\; label="Z"\; filenames="HSA0000101474460000012.png"\; state="\{\{state\}\}">Z</figure-callout>}}_1}\&times;(Z_1-Z_0)$

If be all positioned at and lack the top of surveying layer height, the scarce survey low latitude wind speed degree V of this layer apart from the low latitude wind observed reading that lacks two height surveying the poor minimum of layer height _s0with wind direction V _x0as follows respectively:

$V_{s0}=V_{s1}+\frac{V_{s1}-V_{s2}}{Z_1-{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HSA0000101474460000012.png,HSA0000101474460000022.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2}\&times;(Z_0-Z_1)$

$V_{x0}=V_{x1}+\frac{V_{x1}-V_{x2}}{Z_1-{\mathrm{<figure-callout\; id="2"\; label="Z"\; filenames="HSA0000101474460000012.png,HSA0000101474460000022.png"\; state="\{\{state\}\}">Z</figure-callout>}}_2}\&times;(Z_0-Z_1)$

Wherein, V _s1, V _s2be respectively apart from the low latitude wind speed that lacks two height surveying the poor minimum of layer height, Z ₁, Z ₂be respectively two height surveying the poor minimum of layer height apart from lacking, Z ₀for surveying layer height apart from lacking; V _x1, V _x2be respectively apart from the low latitude wind direction that lacks two height surveying the poor minimum of layer height.

(upper: 00:00:31-03:30:33 in two detection periods of on June 25th, 2013, under: the two-dimentional wind field before and after the scarce survey data that 18:45:27-23:15:35) adopt the inventive method to survey layer to lacking solve is as shown in Fig. 2, Fig. 3, Fig. 4, Fig. 5, as can be seen from the figure, solve by the scarce survey data of surveying layer to lacking, obtained the low latitude wind data of each height layer.

1.3, the overlapping layer low latitude wind wind speed and direction of low latitude, different research station wind observed reading is revised

The overlapping layer of low latitude, different research station wind observed reading is carried out to low latitude wind data and revise, obtain the overlapping layer low latitude wind wind speed and direction of low latitude, different research station wind observed reading.

Overlapping layer low latitude wind wind speed correction to low latitude, different research station wind observed reading is as follows:

Wherein, V _{v orders}for revised overlapping layer low latitude wind wind speed, V _{v surveys}for the measured value of the lower low latitude wind wind speed of precision, what be low latitude, different research station wind wind speed at the long-term mean value of overlapping layer height is poor,

low latitude wind wind speed that precision the is lower long-term mean value at overlapping layer height,

low latitude wind wind speed that precision the is higher long-term mean value at overlapping layer height.

Overlapping layer low latitude wind wind direction correction to low latitude, different research station wind observed reading is as follows:

Wherein, V _{d orders}revised overlapping layer low latitude wind wind direction, V _{d surveys}for the measured value of the lower low latitude wind wind direction of precision,

what be low latitude, different research station wind wind direction at the long-term mean value of overlapping layer height is poor,

low latitude wind wind direction that precision the is lower long-term mean value at overlapping layer height,

low latitude wind wind direction that precision the is higher long-term mean value at overlapping layer height.

Step 2, solve low latitude wind

According to the altitude wind field of setting up, the error between low latitude wind calculated value and the measured value of each layer, through deviation statistics analysis, sets up regression equation and solves low latitude wind.

Solve low latitude wind wind direction

with wind speed

specific as follows:

$\widehat{y_d}=a_0+a_1{V}_d$

${\hat{y}}_v=b_0+b_1{V}_v+b_2{{\mathrm{<figure-callout\; id="2"\; label="V\; v"\; filenames="HSA0000101474460000012.png,HSA0000101474460000022.png"\; state="\{\{state\}\}">V</figure-callout>}}_v}^2$

Wherein,

for the low latitude wind wind direction value solving, V _dfor the low latitude wind wind direction value of equivalent layer in the continuous altitude wind field of step 1 foundation, a ₀, a ₁for one-variable linear regression equation regression coefficient, a ₀with a ₁according to the conception of history measured value of the low latitude wind wind direction of equivalent layer and its corresponding historical calculated value, utilize least square method to determine; for the low latitude wind air speed value solving, V _vfor the low latitude wind air speed value of equivalent layer in the continuous altitude wind field of step 1 foundation, b ₀, b ₁, b ₂for regression equation regression coefficient, b ₀, b ₁, b ₂according to the conception of history measured value of the low latitude wind wind speed of equivalent layer and its corresponding historical calculated value, utilize least square method to determine.

By utilizing method of the present invention, comprehensive utilization anemometer tower low latitude wind data and wind profile radar low latitude wind data, the low latitude wind vector before manned spaceship is returned is quantitatively calculated, and obtains and calculates low latitude wind wind direction June with wind speed

regression equation as follows:

$\widehat{y_d}=61.34+0.72x_d$

${\hat{y}}_v=2.23+0.56x_v+0.01{x_{\mathrm{<figure-callout\; id="2"\; label="v"\; filenames="HSA0000101474460000012.png,HSA0000101474460000022.png"\; state="\{\{state\}\}">v</figure-callout>}}}^2$

Wherein,

for low latitude wind wind direction calculated value, x _dfor the observed reading of low latitude wind wind direction;

for low latitude wind wind speed calculated value, x _vfor the observed reading of low latitude wind wind speed.

The low latitude wind that adopts the present invention to calculate on June 25th, 2013 and the accuracy comparison of the low latitude wind that adopts linear interpolation method to calculate, as shown in Figure 6, as seen from the figure, the low latitude wind that adopts the present invention to calculate is obvious more close to the low latitude wind data of actual measurement, proves that the present invention has significantly improved the computational accuracy of low latitude wind vector.

Claims (4)

1. low latitude wind is determined a method, it is characterized in that: comprise the steps:

Step 1, set up continuous altitude wind field

The low latitude wind data that the different research stations of statistical study provide, by observation data feature, altitude wind field is carried out to layering, the layer of disappearance low latitude wind observed reading is solved to lack and survey data, during for the ply of low latitude, different research station wind observed reading, the low latitude wind data of overlapping layer is revised;

Step 2, solve low latitude wind

Solve low latitude wind wind direction

with wind speed

specific as follows:

$\widehat{y_d}=a_0+a_1{V}_d$

${\hat{y}}_v=b_0+b_1{V}_v+b_2{V_v}^2$

Wherein, V _dfor the low latitude wind wind direction value of equivalent layer in the continuous altitude wind field of step 1 foundation, a ₀, a ₁for one-variable linear regression equation regression coefficient, a ₀with a ₁according to the conception of history measured value of the low latitude wind wind direction of equivalent layer and its corresponding historical calculated value, utilize least square method to determine; V _vfor the low latitude wind air speed value of equivalent layer in the continuous altitude wind field of step 1 foundation, b ₀, b ₁, b ₂for regression equation regression coefficient, b ₀, b ₁, b ₂according to the conception of history measured value of the low latitude wind wind speed of equivalent layer and its corresponding historical calculated value, utilize least square method to determine.

2. low latitude according to claim 1 wind is determined method, it is characterized in that: in described step 1, adopt interpolation method to solve to the layer of disappearance low latitude wind observed reading and lack survey data.

3. low latitude according to claim 1 and 2 wind is determined method, it is characterized in that: it is specific as follows that described employing interpolation method solves scarce survey break survey data:

If lay respectively at and lack below and the top of surveying layer height, the scarce survey low latitude wind speed degree V of this layer apart from the low latitude wind observed reading that lacks two height surveying the poor minimum of layer height _s0with wind direction V _x0as follows respectively:

$V_{s0}=V_{s1}+\frac{V_{s2}-V_{s1}}{Z_2-Z_1}\&times;(Z_0-Z_1)$

$V_{x0}=V_{x1}+\frac{V_{x2}-V_{x1}}{Z_2-Z_1}\&times;(Z_0-Z_1)$

If be all positioned at and lack the below of surveying layer height, the scarce survey low latitude wind speed degree V of this layer apart from the low latitude wind observed reading that lacks two height surveying the poor minimum of layer height _s0with wind direction V _x0as follows respectively:

$V_{s0}=V_{s1}-\frac{V_{s2}-V_{s1}}{Z_2-Z_1}\&times;(Z_1-Z_0)$

$V_{x0}=V_{x1}-\frac{V_{x2}-V_{x1}}{Z_2-Z_1}\&times;(Z_1-Z_0)$

If be all positioned at and lack the top of surveying layer height, the scarce survey low latitude wind speed degree V of this layer apart from the low latitude wind observed reading that lacks two height surveying the poor minimum of layer height _s0with wind direction V _x0as follows respectively:

$V_{s0}=V_{s1}+\frac{V_{s1}-V_{s2}}{Z_1-Z_2}\&times;(Z_0-Z_1)$

$V_{x0}=V_{x1}+\frac{V_{x1}-V_{x2}}{Z_1-Z_2}\&times;(Z_0-Z_1)$

Wherein, V _s1, V _s2be respectively apart from the low latitude wind speed that lacks two height surveying the poor minimum of layer height, Z ₁, Z ₂be respectively two height surveying the poor minimum of layer height apart from lacking, Z ₀for surveying layer height apart from lacking; V _x1, V _x2be respectively apart from the low latitude wind direction that lacks two height surveying the poor minimum of layer height.

4. low latitude according to claim 1 wind is determined method, it is characterized in that: in described step 1, the low latitude wind data correction of low latitude, different research station wind observed reading overlapping layer is as follows:

Overlapping layer low latitude wind wind speed correction to low latitude, different research station wind observed reading is as follows:

Wherein, V _{v orders}for revised overlapping layer low latitude wind wind speed, V _{v surveys}for the measured value of the lower low latitude wind wind speed of precision,

what be low latitude, different research station wind wind speed at the long-term mean value of overlapping layer height is poor,

low latitude wind wind speed that precision the is lower long-term mean value at overlapping layer height,

low latitude wind wind speed that precision the is higher long-term mean value at overlapping layer height;

Overlapping layer low latitude wind wind direction correction to low latitude, different research station wind observed reading is as follows:

Wherein, V _{d orders}revised overlapping layer low latitude wind wind direction, V _{d surveys}for the measured value of the lower low latitude wind wind direction of precision,

what be low latitude, different research station wind wind direction at the long-term mean value of overlapping layer height is poor,

low latitude wind wind direction that precision the is lower long-term mean value at overlapping layer height, low latitude wind wind direction that precision the is higher long-term mean value at overlapping layer height.

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