mg-top.R

# Establish the vector scalar for the currents
current_uv_scalar <- 2

# The top figure (sea)
mg_top <- ggplot(data = southern_africa_coast, aes(x = lon, y = lat)) +
  # The ocean temperature
    geom_raster(data = sea_temp, aes(fill = value)) +
  # The bathymetry
    stat_contour(data = sa_bathy[sa_bathy$depth < -200 & sa_bathy$depth > -2000,], 
                 aes(x = lon, y = lat, z = depth, alpha = ..level..),
                 colour = "ivory", size = 0.5, binwidth = 1000, na.rm = TRUE, show.legend = FALSE) +
  # The current vectors
    geom_segment(data = currents, aes(xend = lon + u * current_uv_scalar, yend = lat + v * current_uv_scalar),
                 arrow = arrow(angle = 15, length = unit(0.02, "inches"), type = "closed"), alpha = 0.4) +
  # The land mass
    geom_polygon(aes(group = group), fill = "grey70", colour = "black", size = 0.5, show.legend = FALSE) +
    geom_path(data = africa_borders, aes(group = group)) +
  # The legend for the vector length
    geom_label(aes(x = 36, y = -37, label = "1.0 m/s\n"), size = 3, label.padding = unit(0.5, "lines")) +
    geom_segment(aes(x = 35, y = -37.5, xend = 37, yend = -37.5)) +
  # The in situ sites
    geom_point(data = site_list, shape = 1,  size = 2.4, colour = "ivory") +
    geom_text(data = site_list, aes(label = order), size = 1.6, colour = "red") +
  # Oceans
    annotate("text", label = "INDIAN\nOCEAN", x = 37.00, y = -34.0, size = 4.0, angle = 0, colour = "ivory") +
    annotate("text", label = "ATLANTIC\nOCEAN", x = 13.10, y = -34.0, size = 4.0, angle = 0, colour = "ivory") +
  # Benguela
    geom_segment(aes(x = 17.2, y = -32.6, xend = 15.2, yend = -29.5),
                arrow = arrow(length = unit(0.3, "cm")), size = 0.5, colour = "ivory") +
    annotate("text", label = "Benguela", x = 16.0, y = -31.8, size = 3.5, angle = 298, colour = "ivory") +
  # Agulhas
    geom_segment(aes(x = 33, y = -29.5, xend = 29.8, yend = -33.0),
                arrow = arrow(length = unit(0.3, "cm")), size = 0.5, colour = "ivory") +
    annotate("text", label = "Agulhas", x = 31.7, y = -31.7, size = 3.5, angle = 53, colour = "ivory") +
  # Agulhas Bank
    annotate("text", label = "Agulhas\nBank", x = 22.5, y = -35.5, size = 3.0, angle = 0, colour = "ivory") +
  # Cape Peninsula
    annotate("text", label = "Cape\nPeninsula", x = 17.2, y = -35, size = 3.0, angle = 0, colour = "ivory") +
  # Improve on the x and y axis labels
    scale_x_continuous(breaks = seq(15, 35, 5),
                       labels = scales::unit_format("°E", sep = ""),
                       position = "top") +
    scale_y_continuous(breaks = seq(-35, -30, 5),
                       labels = c("35°S", "30°S")) +
    labs(x = NULL, y = NULL) +
  # Slightly shrink the plotting area
    coord_cartesian(xlim = c(10.5, 39.5), ylim = c(-39.5, -25.5), expand = F) +
  # Use viridis colour scheme
    scale_fill_viridis(name = "Temp.\n(°C)", option = "D") +
  # Adjust the theme
    theme_bw() +
    theme(panel.border = element_rect(fill = NA, colour = "black", size = 1),
          axis.text = element_text(colour = "black"),
          axis.ticks = element_line(colour = "black"))