This subroutine computes the conversion from condensation to precipitation (snow or rain) or evaporation of rain. More...
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_specific_humidity_updated_by_physics | cloud condensed water specific humidity | 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_stratiform_precipitation_amount | stratiform rainfall 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_model_physics | tendency of rain water mixing ratio due to model physics | 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 | error_message | error message for error handling in CCPP | none | 0 | character | len=* | out | F |
errflg | error_flag | error flag for error handling in CCPP | flag | 0 | integer | out | F |
The following two equations can be used to calculate the precipitation rates of rain and snow at each module 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} ([90]).
The calculation is as follows:
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) |
subroutine zhaocarr_precpd::zhaocarr_precpd_run | ( | integer, intent(in) | im, |
integer, intent(in) | ix, | ||
integer, intent(in) | km, | ||
real (kind=kind_phys), intent(in) | dt, | ||
real (kind=kind_phys), dimension(ix,km), intent(in) | del, | ||
real (kind=kind_phys), dimension(ix,km), intent(in) | prsl, | ||
real (kind=kind_phys), dimension(ix,km), intent(inout) | q, | ||
real (kind=kind_phys), dimension(ix,km), intent(inout) | cwm, | ||
real (kind=kind_phys), dimension(ix,km), intent(inout) | t, | ||
real (kind=kind_phys), dimension(im), intent(out) | rn, | ||
real (kind=kind_phys), dimension(im), intent(out) | sr, | ||
real (kind=kind_phys), dimension(im,km), intent(out) | rainp, | ||
real (kind=kind_phys), dimension(im,km), intent(in) | u00k, | ||
real (kind=kind_phys), dimension(2), intent(in) | psautco, | ||
real (kind=kind_phys), dimension(2), intent(in) | prautco, | ||
real (kind=kind_phys), intent(in) | evpco, | ||
real (kind=kind_phys), dimension(2), intent(in) | wminco, | ||
real (kind=kind_phys), dimension(im), intent(in) | wk1, | ||
logical, intent(in) | lprnt, | ||
integer, intent(in) | jpr, | ||
character(len=*), intent(out) | errmsg, | ||
integer, intent(out) | errflg | ||
) |
cwm > \min (wmin, wmini)
where the cloud water and ice conversion threshold:wmin=wminco(1)\times prsl\times 10^{-5}
wmini=wminco(2)\times prsl\times 10^{-5}
P_{saut}=a_{1}(cwm-wmini)
Since snow production in this process is caused by the increase in size of cloud ice particles due to depositional growth and aggregation of small ice particles, P_{saut} is a function of temperature as determined by coefficient a_{1}, given bya_{1}=psautco \times dt \times exp\left[ 0.025\left(T-273.15\right)\right]
P_{saci}=C_{s}cwm P_{s}
where P_{s} is the precipitation rate of snow. The collection coefficient C_{s} is a function of temperature since the open structures of ice crystals at relative warm temperatures are more likely to stick, given a collision, than crystals of other shapes ([75]). Above the freezing level, C_{s} is expressed byC_{s}=c_{1}exp\left[ 0.025\left(T-273.15\right)\right]
where c_{1}=1.25\times 10^{-3} m^{2}kg^{-1}s^{-1} are used. C_{s} is set to zero below the freezing level.P_{raut}=(prautco \times dt )\times (cwm-wmin)\left\{1-exp[-(\frac{cwm-wmin}{m_{r}b})^{2}]\right\}
where m_{r} is 3.0\times 10^{-4}.E_{rr}= evpco \times (u-f)(P_{r})^{\beta}
where u is u00k, f is the relative humidity. \beta = 0.5 are empirical parameter.E_{rs}=[C_{rs1}+C_{rs2}(T-273.15)](\frac{u-f}{u})P_{s}
where C_{rs1}=5\times 10^{-6}m^{2}kg^{-1}s^{-1} and C_{rs2}=6.67\times 10^{-10}m^{2}kg^{-1}K^{-1}s^{-1}. The evaporation of melting snow below the freezing level is ignored in this scheme because of the difficulty in the latent heat treatment since the surface of a melting snowflake is usually covered by a thin layer of liquid water.P_{sm1}=C_{sm}(T-273.15)^{2}P_{s}
where C_{sm}=5\times 10^{-8}m^{2}kg^{-1}K^{-2}s^{-1} cause the falling snow to melt almost completely before it reaches the T=278.15 K level.P_{sacw}=C_{r}cwmP_{s}
where C_{r} is the collection coefficient, C_{r}=5.0\times 10^{-4}m^{2}kg^{-1}s^{-1} . The melting rate of snow then can be computed fromP_{sm2}=C_{ws}P_{sacw}
where C_{ws}=0.025.t=t-\frac{L}{C_{p}}(E_{rr}+E_{rs}+P_{sm1})\times dt
q=q+(E_{rr}+E_{rs})\times dt
rn= (P_{r}(\eta_{sfc})+P_{s}(\eta_{sfc}))/10^3
sr=\frac{P_{s}(\eta_{sfc})}{P_{s}(\eta_{sfc})+P_{r}(\eta_{sfc})}