API¶

The PyPROS module¶

Functions to calculate the precipitation type. For a point or numpy arrays

class pypros.pros.PyPros(variables_file, method='ks', threshold=None, data_format=None)[source]¶

Main project class. Discriminates precipitation type considering different methodologies using surface observations.

__init__(variables_file, method='ks', threshold=None, data_format=None)[source]¶

Parameters

variables_file (str, list) – The file paths containing air temperature, dew point temperature and (digital elevation model) fields.
method (str) –
The precipitation type discrimination method to use. Defaults to ks.
Available:
- ks : Koistinen and Saltikoff method
- single_tw: A single wet bulb temperature
  threshold
- single_ta: A single air temperature threshold
- dual_tw : A dual wet bulb temperature thresholds
- dual_ta : A dual air temperature threshold
- linear_tr: Linear transition between rain
  and snow
threshold (float, list) –
Threshold value(s) to use in the different methods available.
Defaults to:
- static_tw: 1.5
- static_ta: 0.0
- linear_tr: [0, 3]
data_format (dict, optional) –
Defaults to None. The order of the variables in the variables files. Defaults to: {‘vars_files’: [‘tair’,

’tdew’, ‘dem’]}

Raises

ValueError – Raised when the method is not valid

__weakref__¶: list of weak references to the object (if defined)

refl_mask(refl)[source]¶

Calculates the precipitation type masked. The output classification is as follows:

rain

1dBZ : 1
5dBZ: 2
10dBZ : 3
15dBZ: 4
25dBZ : 5

sleet

1dBZ: 6
5dBZ : 7
10dBZ: 8
15dBZ : 9
25dBZ: 10

snow

1dBZ : 11
5dBZ: 12
10dBZ : 13
15dBZ: 14
25dbZ: 15

Parameters: refl (numpy.array) – Array with reflectivity values
Raises: IndexError – Raised if the types don’t match in size or type
Returns: The precipitation type classification value
Return type: float, numpy array

save_file(field, file_name)[source]¶

Saves the calculate field data into a file

Parameters: file_name (str) – The output file path

Psychrometric calculations¶

Psychrometric calculations

pypros.psychrometrics.get_tw_sadeghi(tair, tdew, z)[source]¶

Gets the wet bulb temperature from air temperature, dew point temperature and pressure. Formula taken from: https://journals.ametsoc.org/doi/pdf/10.1175/JTECH-D-12-00191.1

Results close to trhp2tw, but computationally efficient

Parameters

tair (float, numpy array) – The air temperature in Celsius
tdew (float, numpy array) – The dew point temperature in Celsius
z (float, numpy array) – The altitude in metres

Returns

The wet bulb temperature in Celsius

Return type

float, numpy array

pypros.psychrometrics.hr2td(temp, r_h)[source]¶

Returns the dew point from the relative humidity and the temperature Formula from: https://www.aprweather.com/pages/calc.htm

Both float values or numpy matrices can be passed as input and get as output

Parameters

temp (float, numpy array) – The temperature in Celsius
r_h (float, numpy array) – The relative humidity in %

Returns

The dew point in Celsius

Return type

float, numpy array

pypros.psychrometrics.td2hr(temp, tempd)[source]¶

Returns the relative humidity from the temperature and the dew point Formula from: https://www.aprweather.com/pages/calc.htm

Both float values or numpy matrices can be passed as input and get as output

Parameters

temp (float, numpy array) – The temperature in Celsius
tempd (float, numpy array) – The dew point in Celsius

Returns

The relative humidity in %

Return type

float, numpy array

pypros.psychrometrics.trhp2tw(temp, rh, z)[source]¶

Gets the wet bulb temperature from the temperature, relative humidity and pressure. Formula taken from: https://www.weather.gov/epz/wxcalc_wetbulb (Brice and Hall, 2003)

Parameters

temp (float, numpy array) – The temperature in Celsius
rh (float, numpy array) – The relative humidity in [0,1]
z (float, numpy array) – The altitude in metres

Returns

The wet bulb temperature in Celsius

Return type

float, numpy array

pypros.psychrometrics.ttd2tw(temp, tempd)[source]¶

Gets the wet bulb temperature from the temperature and the dew point Formula taken from: https://journals.ametsoc.org/doi/full/10.1175/JAMC-D-11-0143.1

TODO: Take altitude in account (should change algorithm)

Parameters

temp (float, numpy array) – The temperature in Celsius
tempd (float, numpy array) – The dew point in Celsius

Returns

The wet bulb temperature in Celsius

Return type

float, numpy array

Rain or snow methodologies¶

Implements several rain or snow methodologies.

pypros.ros_methods.calculate_dual_threshold(field, th_s, th_r)[source]¶

Calculates the precipitation type based on two threshold values, one for rain and one for snow. If value >= th_r –> rain –> 0 If value <= th_s –> snow –> 1 If th_s < value < th_r –> mixed –> 0.5

Parameters

field (float, numpy array) – Meteorological variable field
th_s (float) – Snow threshold. Values below this threshold classified as snow.
th_r (float) – Rain threshold. Values above this threshold classified as rain.

Raises

ValueError – Raised if th_r is smaller than th_s.

Returns

Precipitation type field

Return type

float, numpy array

pypros.ros_methods.calculate_koistinen_saltikoff(temp, tempd)[source]¶

Returns the Koistinen-Saltikoff value.

Koistinen J., Saltikoff E. (1998): Experience of customer products of accumulated snow, sleet and rain, COST 75 Final Seminar on Advanced Weather Radar Systems, Locarno, Switzerland. EUR 18567 EN, 397-406.

The formula values are

prob < 0.3 –> rain
0.3 < prob < 0.7 –> sleet
prob > 0.7 –> snow

Both float values or numpy matrices can be passed as input and get as output

Parameters

temp (float, numpy array) – The temperature in Celsius
tempd (float, numpy array) – The dew point in Celsius

Returns

The Koistinen J., Saltikoff E. formula value

Return type

float, numpy array

pypros.ros_methods.calculate_linear_transition(field, th_s, th_r)[source]¶

Calculates the probability of precipitation type based on two threshold values, one for rain and one for snow. Assumes a linear transition between them. If value >= th_r –> rain –> 0 If value <= th_s –> snow –> 1 If th_s < value < th_r –> mixed –> (0, 1)

Parameters

field (float, numpy array) – Meteorological variable field
th_s (float) – Snow threshold. Values below this threshold classified as snow.
th_r (float) – Rain threshold. Values above this threshold classified as rain.

Raises

ValueError – Raised if th_r is smaller than th_s.

Returns

Probability of precipitation type field

Return type

float, numpy array

pypros.ros_methods.calculate_single_threshold(field, th)[source]¶

Calculates the precipitation type based on a threshold value. If value > threshold –> rain –> 0 If value <= threshold –> snow –> 1

Parameters

field (float, numpy array) – Meteorological variable field
th (float) – Threshold from which precipitation type is discriminated

Returns

Precipitation type field

Return type

float, numpy array