dfm_functions.py

# coding: utf-8

# In[ ]:

def estimate_relative_humidity(q,t_avg,lat,lon):
    ## estimates relative humidity using hypsometric equation for pressure, virtual temperature and 
    ## average temperature 
    import numpy as np
    from snowpack_functions import get_elev_for_lat_lon,import_gridcell_elevation 
    #################### CONSTANTS ###############################
    Rd = 287.04 ## J kg^-1 K ^-1
    p1 = 100000 ## Pa
    T0 = 273.15 ## reference temperature
    g = 9.81 ## m / s^2
    
    ## need to get elevations for grid cells
    soil_file = '/raid9/gergel/agg_snowpack/soil_avail.txt'
    elev_corr_info = import_gridcell_elevation(soil_file) 
    h = get_elev_for_lat_lon(elev_corr_info,lat,lon)
    
    ##  Tv = T(1 + 0.61w)
    Tv = t_avg * (1 + 0.61*q)
    ## p = e ^ (-(((z_2 - z_1) * g)/ (Rd*Tv) - ln(p1)))
    hg = h * g
    RdTv = Rd * Tv

    p = np.exp(-((np.divide(hg,RdTv.air_temp_min)) - math.log(p1)))
    ## RH = 0.263*p*q[exp(17.67*T - T0)/(T - 29.65)]^-1
    
    RH = 0.263*p*q * ((np.exp((17.67 * (t_avg - T0))/ (t_avg - 29.65)))**-1)
    
    return (RH)

def estimate_emc(RH,t):
    if RH < 10: 
        EMC = 0.03229 + 0.281073*RH - 0.000578*t_avg*RH
    elif RH >= 10 and RH <= 50:
        EMC = 2.22749 - 0.160107*RH - 0.014784*t_avg
    else: 
        EMC = 21.0606 + (0.005565*(RH**2)) - (0.00035*RH*t_avg) - (0.483199*RH)
    return(EMC)

def nfdrs_climate_class(lon):
    ## use eastern boundary of the Cascades to delineate (this might need refinement)
    if lon > -120.5:
        climate_class = 2
        wetrat = 0.25
    else:
        climate_class = 3
        wetrat = 0.05
    return(climate_class,wetrat)