def METHOD_NAME():
    """
    Returns a full list of all nights availabel in the DESI Raw data directory.
    Returns:
        nights, list. A list of nights on or after Jan 1 2020 in which data exists at NERSC.
    """
    nights = list()
    for n in listpath(os.getenv('DESI_SPECTRO_DATA')):
        # - nights are 202YMMDD
        if re.match('^202\d{5}$', n):
            nights.append(int(n))
    return nights