def calc_hov(da, lat1, lat2, dim='lat'):
    """Function to calculate Hovmoeller field
    ---------------------------------------------
    Parameters:
    da: xarray dataarray
    lat1, lat2: (int) latitude band to use for averaging
    dim: (str) dimension to average along
    ----------------------------------------------
    Returns:
    xarray dataarray
        """
    return da.sel(lat=slice(lat1, lat2)).mean(dim)