docs: def split_tracks(lat,lon,*args):
          '''assumes eastward motion'''
          tracks = []
          lt,ln = [lat[0]],[lon[0]]
          zz = [[z[0]] for z in args]
          for i in range(1,len(lon)):
              lt.append(lat[i])
              for z,a in zip(zz,args):
                  z.append(a[i])
              d1 = abs(lon[i] - lon[i-1])
              d2 = abs((lon[i-1] + 360) - lon[i])
              d3 = abs(lon[i-1] - (lon[i] + 360))
              if d2 < d1:
                  ln.append(lon[i]-360)
                  tracks.append([np.array(lt),np.array(ln)] \
                      + [np.array(z) for z in zz])
                  lt = [lat[i-1],lat[i]]
                  ln = [lon[i-1]+360,lon[i]]
                  zz = [[z[i-1]] for z in args]
              elif d3 < d1:
                  ln.append(lon[i]+360)
                  tracks.append([np.array(lt),np.array(ln)] \
                      + [np.array(z) for z in zz])
                  lt = [lat[i-1],lat[i]]
                  ln = [lon[i-1]-360,lon[i]]
                  zz = [[z[i-1],z[i]] for z in args]
              else:
                  ln.append(lon[i])
          if len(lt):
              tracks.append([np.array(lt),np.array(ln)] \
                  + [np.array(z) for z in zz])
          return tracks