如何从 R 中的 U 和 V 风分量计算风向 [英] How to calculate wind direction from U and V wind components in R

问题描述

我有 U 和 V 风分量数据，我想根据 R 中的这些值计算风向.

I have U and V wind component data and I would like to calculate wind direction from these values in R.

我想最终得到 0-360 度范围内的风向数据，0° 或 360° 表示风向北吹，90° 表示风向东吹，180° 表示风向风向南吹，270° 表示风向西吹.

I would like to end up with wind direction data on a scale of 0-360 degrees, with 0° or 360° indicating a wind blowing to the north, 90° indicating a wind blowing to the east, 180° indicating a wind blowing to the south and 270° indicating a wind blowing to the west.

以下是一些示例数据:

> dput(wind)
structure(list(u_ms = c(-3.711, -2.2417, -1.8188, -1.6164, -1.3941, 
-1.0682, -0.57611, -1.5698, -1.4976, -1.3537, -1.0901, -0.60403, 
-0.70812, -0.49045, -0.39849, 0.17875, 0.48356, 1.5082, 1.4219, 
2.5881), v_ms = c(-1.471, -1.6118, -1.6613, -1.7037, -1.7388, 
-1.8748, -1.8359, -1.6766, -1.6994, -1.7505, -1.4947, -0.96283, 
-1.1194, -0.6849, -0.7847, -0.80349, -0.19352, -0.97815, -1.0835, 
-0.81666), u_rad = c(-0.064769155, -0.039125038, -0.031744042, 
-0.028211496, -0.02433163, -0.018643603, -0.010055014, -0.027398173, 
-0.026138045, -0.023626517, -0.01902583, -0.01054231, -0.012359023, 
-0.008559966, -0.006954961, 0.003119775, 0.008439712, 0.02632305, 
0.024816831, 0.045170857), v_rad = c(-0.025673788, -0.028131211, 
-0.028995149, -0.029735168, -0.030347779, -0.032721426, -0.032042493, 
-0.029262184, -0.029660119, -0.030551982, -0.026087431, -0.01680455, 
-0.019537212, -0.011953758, -0.013695596, -0.014023543, -0.00337756, 
-0.017071935, -0.018910639, -0.014253403)), .Names = c("u_ms", 
"v_ms", "u_rad", "v_rad"), class = "data.frame", row.names = c(NA, 
-20L))

我使用以下代码尝试获取风向(td 列)，但我不相信返回的角度是我想要的(即 0°/360° 表示一个风向北吹，90°表示风向东吹等等……).

I have used the following code to try and obtain wind direction (column td), but I am not convinced that the returned angles are those that I want (i.e. 0°/360° indicating a wind blowing to the north, 90° indicating a wind blowing to the east etc…).

u = wind$u_rad # u component in radians
v = wind$v_rad # v component in radians

d = (180/pi)*(atan2(u,v))
td = as.matrix(d + 180)
df = cbind(wind, d, td)

> df
       u_ms     v_ms        u_rad       v_rad         d        td
1  -3.71100 -1.47100 -0.064769155 -0.02567379 -111.6228  68.37716
2  -2.24170 -1.61180 -0.039125038 -0.02813121 -125.7164  54.28357
3  -1.81880 -1.66130 -0.031744042 -0.02899515 -132.4087  47.59129
4  -1.61640 -1.70370 -0.028211496 -0.02973517 -136.5062  43.49379
5  -1.39410 -1.73880 -0.024331630 -0.03034778 -141.2788  38.72124
6  -1.06820 -1.87480 -0.018643603 -0.03272143 -150.3269  29.67308
7  -0.57611 -1.83590 -0.010055014 -0.03204249 -162.5780  17.42199
8  -1.56980 -1.67660 -0.027398173 -0.02926218 -136.8842  43.11576
9  -1.49760 -1.69940 -0.026138045 -0.02966012 -138.6118  41.38819
10 -1.35370 -1.75050 -0.023626517 -0.03055198 -142.2844  37.71557
11 -1.09010 -1.49470 -0.019025830 -0.02608743 -143.8963  36.10365
12 -0.60403 -0.96283 -0.010542310 -0.01680455 -147.8980  32.10204
13 -0.70812 -1.11940 -0.012359023 -0.01953721 -147.6830  32.31699
14 -0.49045 -0.68490 -0.008559966 -0.01195376 -144.3939  35.60607
15 -0.39849 -0.78470 -0.006954961 -0.01369560 -153.0774  26.92258
16  0.17875 -0.80349  0.003119775 -0.01402354  167.4578 347.45783
17  0.48356 -0.19352  0.008439712 -0.00337756  111.8112 291.81121
18  1.50820 -0.97815  0.026323050 -0.01707193  122.9656 302.96561
19  1.42190 -1.08350  0.024816831 -0.01891064  127.3077 307.30771
20  2.58810 -0.81666  0.045170857 -0.01425340  107.5128 287.51279

对于我的方法是否正确以及如何正确获得所需的风向值的任何建议，我将不胜感激.虽然 计算使用 lapply 或 ifelse 的风的 U 和 V 分量的风向很有帮助，代码确实适用于我的数据，我相信有一个更容易获得风向的方法.非常感谢！

I would appreciate any advice on whether my method is correct, and if not how I could correctly obtain the desired wind direction values. While Calculating wind direction from U and V components of the wind using lapply or ifelse was helpful, the code did work with my data, and I am sure that there is an easier away to obtain wind direction. Many thanks!

推荐答案

这有三个问题:

1. 您无法将 m/s 转换为弧度.为了将风分量输入到 atan2 中，您必须对它们进行归一化，但是您不能通过将 m/s 乘以 pi/180(您这样做是为了得到u_rad 和 v_rad).您应该制作一列绝对风速 (sqrt(u_ms^2 + v_ms^2)) 并取 atan2(u_ms/wind_abs, v_ms/wind_abs).(另请注意，atan2 首先采用 y 组件 - 确保这是您想要的)
2. atan2 会给你一个单位圆坐标的答案，它逆时针增加并且在 x 轴上有一个零.您需要基数坐标的答案，该坐标顺时针增加并在 y 轴上为零.要将单位圆转换为基数坐标，您必须从 90 中减去单位圆角.
3. 您必须知道风信息是指风来的方向(基数坐标的标准)还是风吹的方向(三角/矢量操作的标准)

1. You cannot convert m/s to radians. In order to input wind components into atan2, you must normalize them, but you don't do this by multiplying m/s by pi/180 (which you did to get u_rad and v_rad). You should make a column of absolute windspeed (sqrt(u_ms^2 + v_ms^2)) and take atan2(u_ms/wind_abs, v_ms/wind_abs). (also note that atan2 takes y component first - make sure that's what you want)
2. atan2 will give you an answer in the unit circle coordinates, which increase counterclockwise and have a zero on the x-axis. You want an answer in cardinal coordinates which increase clockwise and have a zero on the y-axis. To convert unit circle to cardinal coordinates, you must subtract the unit circle angle from 90.
3. You must know whether the wind info refers to the direction the wind is coming from (standard for cardinal coordinates) or the direction the wind is blowing (standard for trig/vector operations)

如果给定 u_ms == -3.711 和 v_ms = -1.471(在单位圆上，它向下吹并稍微向左吹，所以它来了来自东北)，然后:

If you are given u_ms = = -3.711 and v_ms = -1.471 (on the unit circle it is blowing down and slightly to the left, so it is coming from the northeast), then:

wind_abs = sqrt(u_ms^2 + v_ms^2)
wind_dir_trig_to = atan2(u_ms/wind_abs, v_ms/wind_abs) 
wind_dir_trig_to_degrees = wind_dir_trig_to * 180/pi ## -111.6 degrees

然后您必须将此风向量转换为风来方向的气象约定:

Then you must convert this wind vector to the meteorological convention of the direction the wind is coming from:

wind_dir_trig_from_degrees = wind_dir_trig_to_degrees + 180 ## 68.38 degrees

然后您必须将该角度从三角"坐标转换为基数坐标:

Then you must convert that angle from "trig" coordinates to cardinal coordinates:

wind_dir_cardinal = 90 - wind_dir_trig_from_degrees
[1] 21.62284 #From the northeast.

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