plot_SST_around_Japan_v2.R

pacman::p_load(
  rvest,
  ncdf4,
  sf,
  rnaturalearth,
  tidyverse,
  reshape2,
  scales)


box = c(xmin = 125, ymin = 25, xmax = 150, ymax = 50)
sf_use_s2(FALSE)
aroundJapan <- ne_countries(scale = "large",
                     returnclass = "sf") |> st_crop(box) 


URL_base <- "https://www.ncei.noaa.gov/data/sea-surface-temperature-optimum-interpolation/v2.1/access/avhrr/"
lastDir <- read_html(URL_base) |>
  html_nodes("a") |>
  html_attr("href") |>
  tail(1)  
lastFile <- read_html(paste0(URL_base, lastDir)) |>
                        html_nodes("a") |>
                        html_attr("href") |>
                        tail(1)
download.file(paste0(URL_base, lastDir, lastFile), 
              destfile = file.path(tempdir(), lastFile), mode = "wb")

YMD <- ymd(substr(strsplit(lastFile , "\\.")[[1]][2], 1, 8))

nc4data <- nc_open(file.path(tempdir(), lastFile))
sst <- as.vector(ncvar_get(nc4data, "sst")) 
melt(matrix(sst, ncol = 1440, byrow =T)) |> 
  filter(value != is.na(value)) |> 
  mutate(lon = Var2 / 4 -  0.125,
         lat = Var1 / 4 - 90.125) |> 
  select(lon, lat, sst = value) |> 
  filter(lon >= 125) |> 
  filter(lon <= 150) |> 
  filter(lat >=  25) |> 
  filter(lat <=  50) |> 
  ggplot() +
  geom_point(aes(x = lon, y = lat, color = sst), size = 2) +
  geom_sf(data = aroundJapan, linewidth = 0.1, 
          color = "gray60", fill = "#dcffca") +
  scale_color_gradient2(low = muted("blue"), mid = "white",
                        high = "red", midpoint = 15,
                        breaks = c(0, 5, 10, 15, 20, 25, 30)) +
  annotate("text", x = 130 , y = 48.5, label = YMD, 
           color = "black", size = 3.5) +
  xlim(c(125, 150)) + ylim(c(25, 50)) +
  labs(color = "SST(°C)") +
  theme_void() +
  theme(plot.margin= unit(c(1, 1, 1, 1), "lines"),
        legend.title = element_text(size = rel(0.8)))