def ice_days(tasmax: xarray.DataArray, freq: str = "YS"):
r"""Number of ice/freezing days
Number of days where daily maximum temperatures are below 0℃.
Parameters
----------
tasmax : xarray.DataArray
Maximum daily temperature [℃] or [K]
freq : str
Resampling frequency; Defaults to "YS" (yearly).
Returns
-------
xarray.DataArray
Number of ice/freezing days.
Notes
-----
Let :math:`TX_{ij}` be the daily maximum temperature at day :math:`i` of period :math:`j`. Then
counted is the number of days where:
.. math::
TX_{ij} < 0℃
"""
tu = units.parse_units(tasmax.attrs["units"].replace("-", "**-"))
fu = "degC"
frz = 0
if fu != tu:
frz = units.convert(frz, fu, tu)
f = (tasmax < frz) * 1
return f.resample(time=freq).sum(dim="time")
def ice_days(tasmax, freq='YS'):
r"""Number of ice/freezing days
Number of days where daily maximum temperatures are below 0℃.
Parameters
----------
tasmax : xarrray.DataArray
Maximum daily temperature [℃] or [K]
freq : str, optional
Resampling frequency
Returns
-------
xarray.DataArray
Number of ice/freezing days.
Notes
-----
Let :math:`TX_{ij}` be the daily maximum temperature at day :math:`i` of period :math:`j`. Then
counted is the number of days where:
.. math::
TX_{ij} < 0℃
"""
tu = units.parse_units(tasmax.attrs['units'].replace('-', '**-'))
fu = 'degC'
frz = 0
if fu != tu:
frz = units.convert(frz, fu, tu)
f = (tasmax < frz) * 1
return f.resample(time=freq).sum(dim='time')
def frost_days(tasmin, freq="YS"):
r"""Frost days index
Number of days where daily minimum temperatures are below 0℃.
Parameters
----------
tasmin : xarray.DataArray
Minimum daily temperature [℃] or [K]
freq : str, optional
Resampling frequency
Returns
-------
xarray.DataArray
Frost days index.
Notes
-----
Let :math:`TN_{ij}` be the daily minimum temperature at day :math:`i` of period :math:`j`. Then
counted is the number of days where:
.. math::
TN_{ij} < 0℃
"""
tu = units.parse_units(tasmin.attrs["units"].replace("-", "**-"))
fu = "degC"
frz = 0
if fu != tu:
frz = units.convert(frz, fu, tu)
f = (tasmin < frz) * 1
return f.resample(time=freq).sum(dim="time")
def liquid_precip_ratio(
pr: xarray.DataArray,
prsn: xarray.DataArray = None,
tas: xarray.DataArray = None,
freq: str = "QS-DEC",
) -> xarray.DataArray:
r"""Ratio of rainfall to total precipitation
The ratio of total liquid precipitation over the total precipitation. If solid precipitation is not provided,
then precipitation is assumed solid if the temperature is below 0°C.
Parameters
----------
pr : xarray.DataArray
Mean daily precipitation flux [Kg m-2 s-1] or [mm].
prsn : xarray.DataArray
Mean daily solid precipitation flux [Kg m-2 s-1] or [mm].
tas : xarray.DataArray
Mean daily temperature [℃] or [K]
freq : str
Resampling frequency; Defaults to "QS-DEC".
Returns
-------
xarray.DataArray
Ratio of rainfall to total precipitation
Notes
-----
Let :math:`PR_i` be the mean daily precipitation of day :math:`i`, then for a period :math:`j` starting at
day :math:`a` and finishing on day :math:`b`:
.. math::
PR_{ij} = \sum_{i=a}^{b} PR_i
PRwet_{ij}
See also
--------
winter_rain_ratio
"""
if prsn is None:
tu = units.parse_units(tas.attrs["units"].replace("-", "**-"))
fu = "degC"
frz = 0
if fu != tu:
frz = units.convert(frz, fu, tu)
prsn = pr.where(tas < frz, 0)
tot = pr.resample(time=freq).sum(dim="time")
rain = tot - prsn.resample(time=freq).sum(dim="time")
ratio = rain / tot
return ratio
def consecutive_frost_days(tasmin: xarray.DataArray, freq: str = "AS-JUL"):
r"""Maximum number of consecutive frost days (Tmin < 0℃).
Resample the daily minimum temperature series by computing the maximum number
of days below the freezing point over each period.
Parameters
----------
tasmin : xarray.DataArray
Minimum daily temperature values [℃] or [K]
freq : str
Resampling frequency; Defaults to "YS" (yearly).
Returns
-------
xarray.DataArray
The maximum number of consecutive days below the freezing point.
Notes
-----
Let :math:`\mathbf{x}=x_0, x_1, \ldots, x_n` be a daily minimum temperature series and
:math:`\mathbf{s}` be the sorted vector of indices :math:`i` where :math:`[p_i < 0^\circ C] \neq [p_{i+1} <
0^\circ C]`, that is, the days when the temperature crosses the freezing point.
Then the maximum number of consecutive frost days is given by
.. math::
\max(\mathbf{d}) \quad \mathrm{where} \quad d_j = (s_j - s_{j-1}) [x_{s_j} > 0^\circ C]
where :math:`[P]` is 1 if :math:`P` is true, and 0 if false. Note that this formula does not handle sequences at
the start and end of the series, but the numerical algorithm does.
"""
tu = units.parse_units(tasmin.attrs["units"].replace("-", "**-"))
fu = "degC"
frz = 0
if fu != tu:
frz = units.convert(frz, fu, tu)
group = (tasmin < frz).resample(time=freq)
return group.apply(rl.longest_run, dim="time")