Source code for pycif.plugins.transforms.complex.diagmet.utils.low_cloud_top

import numpy as np




def low_cloud_top(transf, inout_datastore, ddi, mapper):
    """Compute the top pressure of the low cloud layer from relative humidity and temperature.

    Relative humidity is derived at every level from the Tetens saturation
    vapour pressure formula. Outputs the surface relative humidity (``sreh``)
    and stores a below-1000 m maximum relative humidity (``rhmaxx``, clipped to
    :math:`[0.90, 1]`) in ``transf.diag_misc`` for use by
    :func:`~pycif.plugins.transforms.complex.diagmet.utils.vertical_turbulent_diffusivity.vertical_turbulent_diffusivity`.
    See :doc:`/documentation/doc-models/chimere/diagmet` (section 9) for the
    full derivation.

    Args:
        transf (Plugin): diagmet transform instance.
        inout_datastore (dict): mutable datastore.
        ddi (datetime): current sub-simulation date.
        mapper (dict): transform mapper.
    """
    # Parameters
    crhx = 0.90  # Min RH for cloud BLH enhancement
    topcldmax = 1000.
    
    # Inputs
    temp = transf.diag_misc["temp"]
    sphu = transf.diag_misc["sphu"]
    pres = transf.diag_misc["pres"]
    alti = transf.diag_misc["alti"]
    
    # Compute rh
    vapp = 611. * np.exp(17.27 * (temp - 273.15) / (temp - 35.86))
    qsbt = 0.622 * vapp / (pres - vapp)
    rh = sphu / qsbt
    
    ntime, nlev, nlat, nlon = alti.shape
    ind_cloud = np.maximum(0, np.argmin(alti <= topcldmax, axis=1) - 1)
    t, i, j = np.meshgrid(np.arange(ntime), np.arange(nlat), np.arange(nlon),
                          indexing="ij")
    rhmaxx = np.minimum(1., np.maximum(crhx, rh[t, ind_cloud, i, j]))
    
    # Save for later
    transf.diag_misc["rhmaxx"] = rhmaxx
    transf.diag_misc["rh"] = rh

    ref_dataarray = 0 * inout_datastore["outputs"][("meteo", "hght")][ddi]["spec"]
    inout_datastore["outputs"][("meteo", "sreh")][ddi]["spec"] = \
        ref_dataarray + np.minimum(1, np.maximum(rh[:, [0]], 0))