GFS precpd Main

This subroutine computes the conversion from condensation to precipitation (snow or rain) or evaporation of rain. More...

Detailed Description

Argument Table

local_name	standard_name	long_name	units	rank	type	kind	intent	optional
im	horizontal_loop_extent	horizontal loop extent	count	0	integer		in	F
ix	horizontal_dimension	horizontal dimension	count	0	integer		in	F
km	vertical_dimension	vertical layer dimension	count	0	integer		in	F
dt	time_step_for_physics	physics time step	s	0	real	kind_phys	in	F
del	air_pressure_difference_between_midlayers	pressure level thickness	Pa	2	real	kind_phys	in	F
prsl	air_pressure	layer mean pressure	Pa	2	real	kind_phys	in	F
q	water_vapor_specific_humidity_updated_by_physics	water vapor specific humidity	kg kg-1	2	real	kind_phys	inout	F
cwm	cloud_condensed_water_mixing_ratio_updated_by_physics	moist cloud condensed water mixing ratio	kg kg-1	2	real	kind_phys	inout	F
t	air_temperature_updated_by_physics	layer mean air temperature	K	2	real	kind_phys	inout	F
rn	lwe_thickness_of_explicit_precipitation_amount	explicit precipitation amount on physics timestep	m	1	real	kind_phys	out	F
sr	ratio_of_snowfall_to_rainfall	ratio of snowfall to large-scale rainfall	frac	1	real	kind_phys	out	F
rainp	tendency_of_rain_water_mixing_ratio_due_to_microphysics	tendency of rain water mixing ratio due to microphysics	kg kg-1 s-1	2	real	kind_phys	out	F
u00k	critical_relative_humidity	critical relative humidity	frac	2	real	kind_phys	in	F
psautco	coefficient_from_cloud_ice_to_snow	conversion coefficient from cloud ice to snow	none	1	real	kind_phys	in	F
prautco	coefficient_from_cloud_water_to_rain	conversion coefficient from cloud water to rain	none	1	real	kind_phys	in	F
evpco	coefficient_for_evaporation_of_rainfall	coefficient for evaporation of rainfall	none	0	real	kind_phys	in	F
wminco	cloud_condensed_water_conversion_threshold	conversion coefficient from cloud liquid and ice to precipitation	none	1	real	kind_phys	in	F
wk1	grid_size_related_coefficient_used_in_scale-sensitive_schemes	grid size related coefficient used in scale-sensitive schemes	none	1	real	kind_phys	in	F
lprnt	flag_print	flag for printing diagnostics to output	flag	0	logical		in	F
jpr	horizontal_index_of_printed_column	horizontal index of printed column	index	0	integer		in	F
errmsg	ccpp_error_message	error message for error handling in CCPP	none	0	character	len=*	out	F
errflg	ccpp_error_flag	error flag for error handling in CCPP	flag	0	integer		out	F

GFS precpd Scheme General Algorithm

The following two equations can be used to calculate the precipitation rates of rain and snow at each model level:

\[ P_{r}(\eta)=\frac{p_{s}-p_{t}}{g\eta_{s}}\int_{\eta}^{\eta_{t}}(P_{raut}+P_{racw}+P_{sacw}+P_{sm1}+P_{sm2}-E_{rr})d\eta \]

and

\[ P_{s}(\eta)=\frac{p_{s}-p_{t}}{g\eta_{s}}\int_{\eta}^{\eta_{t}}(P_{saut}+P_{saci}-P_{sm1}-P_{sm2}-E_{rs})d\eta \]

where \(p_{s}\) and \(p_{t}\) are the surface pressure and the pressure at the top of model domain, respectively, and \(g\) is gravity. The implementation of the precipitation scheme also includes a simplified procedure of computing \(P_{r}\) and \(P_{s}\) (Zhao and Carr (1997) [111]).

The calculation is as follows:

1. Calculate precipitation production by auto conversion and accretion ( \(P_{saut}\), \(P_{saci}\), \(P_{raut}\)).
   • The accretion of cloud water by rain, \(P_{racw}\), is not included in the current operational scheme.
2. Calculate evaporation of precipitation ( \(E_{rr}\) and \(E_{rs}\)).
3. Calculate melting of snow ( \(P_{sm1}\) and \(P_{sm2}\), \(P_{sacw}\)).
4. Update t and q due to precipitation (snow or rain) production.
5. Calculate precipitation at surface ( \(rn\)) and fraction of frozen precipitation ( \(sr\)).

GFS precpd Scheme Detailed Algorithm

Functions/Subroutines
subroutine	zhaocarr_precpd::zhaocarr_precpd_run (im, ix, km, dt, del, prsl, q, cwm, t, rn, sr, rainp, u00k, psautco, prautco, evpco, wminco , wk1, lprnt, jpr, errmsg, errflg)