#!/usr/bin/env python
# Wenchang Yang (wenchang@princeton.edu)
# Tue Apr 30 16:39:22 EDT 2019
import os, os.path, sys
import cdsapi
c = cdsapi.Client()

# params
data_name = 'vorticity'
plev = '850'
years = range(1979,2019)

# function
def download(data_name, year):
    '''download data from ERA5 in the specified year'''
    ofile = f'era5.{data_name}.{plev}.{year}.nc'
    if os.path.exists(ofile):
        print('[exists]:', ofile)
        return
    c.retrieve(
    'reanalysis-era5-pressure-levels',
    {
        'product_type':'reanalysis',
        'format':'netcdf',
        'pressure_level':plev,
        'variable':data_name,
        'year':f'{year}',
        'month':[
            '01','02','03',
            '04','05','06',
            '07','08','09',
            '10','11','12'
        ],
        'day':[
            '01','02','03',
            '04','05','06',
            '07','08','09',
            '10','11','12',
            '13','14','15',
            '16','17','18',
            '19','20','21',
            '22','23','24',
            '25','26','27',
            '28','29','30',
            '31'
        ],
        'time':[
            '00:00',
            '06:00',
            '12:00',
            '18:00',
        ]
    },
    ofile)    

# run the script
if __name__ == '__main__':
    for year in years:
        download(data_name, year)