如何使用matplotlib在cartopy极地赤平地形图中获得平滑的网格线？

import cartopy.crs as ccrs
import matplotlib.pyplot as plt
import numpy as np

fig = plt.figure(figsize=(10, 10))
ax = fig.add_subplot(1, 1, 1, projection=ccrs.NorthPolarStereo())

ax.set_extent([-180, 180, 60, 90], ccrs.PlateCarree())
ax.background_patch.set_facecolor('lightblue')

ax.stock_img()
ax.coastlines()

gl = ax.gridlines(crs=ccrs.PlateCarree(), linewidth=1, color='gray', alpha=0.5, linestyle='--')
gl.xlocator = mticker.FixedLocator(np.arange(-180, 181, 30))
gl.ylocator = mticker.FixedLocator(np.arange(60, 91, 10))
gl.xformatter = LONGITUDE_FORMATTER
gl.yformatter = LATITUDE_FORMATTER
gl.xlabel_style = {'size': 10, 'color': 'gray'}
gl.ylabel_style = {'size': 10, 'color': 'gray'}

# 添加数据和其他图层的代码

plt.show()