diagramme de lignes de courant

Code R de l'exemple ggplot2

library(ggplot2)
library(metR)

## 10 m wind over London on 3 August 2024 at 8 pm (Met Office UKV model,
## 2 km), 12 x 8 points. The model cells are not quite aligned: each point
## is placed on a regular grid by its rank in longitude and in latitude.
lon <- c(-0.507, -0.432, -0.359, -0.276, -0.204, -0.128, -0.049, 0.027, 0.103, 0.182, 0.258, 0.334)
lat <- c(51.287, 51.344, 51.404, 51.461, 51.518, 51.576, 51.633, 51.693)
## Speed (km/h) and direction the wind blows from (degrees), row by row from
## the south, west to east within each row.
speed <- c(10.8, 8.6, 10.4, 9.4, 10.1, 10.1, 10.4, 8.6, 11.5, 12.6, 11.9, 10.8,
           8.6, 9.4, 10.1, 10.4, 11.5, 10.4, 10.1, 11.5, 10.1, 14, 14, 14.4,
           13.7, 14, 13.7, 13.7, 12.6, 13.7, 13, 11.5, 8.3, 10.4, 14.4, 15.1,
           14, 13.7, 13.7, 12.6, 13.3, 12.2, 11.2, 13, 12.2, 12.2, 11.9, 10.4,
           11.2, 11.5, 11.9, 13.7, 13.7, 14, 13.7, 13.7, 13.7, 13, 13, 13,
           9.4, 10.1, 13.7, 13.3, 14, 14.4, 15.8, 13.7, 11.5, 12.2, 14, 13.7,
           10.8, 10.8, 12.2, 11.9, 13.3, 14.4, 13.3, 10.4, 11.5, 11.2, 11.2, 11.9,
           10.4, 10.4, 10.4, 11.2, 10.4, 9.4, 8.3, 9.7, 10.1, 9.7, 11.2, 10.4)
from <- c(257, 261, 275, 274, 265, 259, 265, 214, 204, 216, 221, 228,
          278, 274, 271, 276, 259, 247, 240, 231, 201, 209, 211, 215,
          314, 321, 324, 315, 308, 294, 280, 280, 240, 212, 215, 221,
          312, 314, 313, 315, 309, 304, 289, 301, 284, 290, 295, 285,
          302, 308, 314, 312, 309, 308, 307, 307, 311, 321, 320, 319,
          300, 308, 309, 307, 300, 298, 298, 301, 320, 323, 320, 317,
          302, 300, 300, 293, 288, 287, 290, 310, 316, 308, 310, 308,
          300, 303, 299, 292, 292, 294, 296, 298, 300, 301, 307, 311)

wind <- expand.grid(lon = lon, lat = lat)
## A wind from `from` degrees blows towards the opposite direction; m/s,
## then degrees of longitude and latitude per second for the integration.
wind$u <- -speed / 3.6 * sin(from * pi / 180)
wind$v <- -speed / 3.6 * cos(from * pi / 180)
wind$dx <- dlon(wind$u, wind$lat)
wind$dy <- dlat(wind$v)

p <- ggplot(wind, aes(x = lon, y = lat)) +
  geom_streamline(aes(dx = dx, dy = dy), L = 2, res = 0.8, jitter = 0,
                  colour = lex_colors[["blue"]], linewidth = 0.3,
                  arrow.length = 0.25, arrow.angle = 20) +
  scale_x_continuous(labels = \(x) paste0(abs(x), "°", ifelse(x < 0, "W", ifelse(x > 0, "E", ""))),
                     expand = expansion(0)) +
  scale_y_continuous(labels = \(y) paste0(y, "°N"), expand = expansion(0)) +
  coord_quickmap() +
  labs(title = "Southwesterly and northwesterly winds converge\nover southeast London",
       subtitle = "10 m wind streamlines, 8 pm, 3 August 2024",
       x = NULL, y = NULL,
       caption = "Data: Met Office UKV model, via Open-Meteo.com (CC BY 4.0)") +
  theme_lex_viz(grid = "", arrows = "") +
  theme(plot.title.position = "plot")