If LWC>LWCAP
then
EXCESS_LWC = LWC-LWCAP
(5)
MELT_I = 0
MELT_II = MELTP
RAIN_IN_I = 0
RAIN_IN_II = RAINs
Else
EXCESS_LWC = 0
MELT_I = MELTP
MELT_II = 0
RAIN_IN_I = RAINs
RAIN_IN_II = 0.
(6)
Equations 710 are ancillary to eq 1 and 2.* Equation 7 calculates the solid water content of new
snow. The units of SNOWs are millimeters of depth/hour because the value of SNOWs for every
time interval represents the amount of newly fallen snow per hour. Equation 8 is the product of SWI,
POR, and SDEP. For simplification, SWI, POR, and SDEP do not appear in Figure 9. Equations 9
and 10 cause improper simulation of melting and refreezing. To better simulate melting and re-
freezing, eq 9 and 10 were revised as eq 11 and 12:
SNOWE = SNOW NEWDEN
(7)
LWCAP = SWI POR SDEP
(8)
MELTP = KMa (TEMPs-TBAS)
If
TEMPs > TBAS
then
If
TEMPs <= TBAS
then
MELTP = 0
(9)
REFREZP = KF (TBAS-TEMPs)
If
TEMPs < TBAS
then
If
TEMPs > = TBAS
then
REFREZP = 0
(10)
For example, eq 9 and 10 say that: if the temperature of the air is greater than that of the snowpack,
then melting occurs; if the air temperature is less than or equal to that of the snowpack, freezing
occurs. Therefore, in this condition when the TEMPs is 0C and TBAS is 1C, the model will melt
the solid ice when, in theory, any existing liquid water should be freezing. This flaw would be found
within the code of MELTP and REFREZP within GAWSER. This problem is solved by using a
temperature switch (Fig. 10) and setting the temperature of the snowpack (TBAS) to zero. The
switch is a single converter with the value of 0C for the entire simulation period. The logic state-
ments within MELTP and REFREZP now use the value in TEMPSWITCH to determine whether
melting or refreezing should occur. The code has been changed to:
MELTP = KMa (TEMPsTBAS)
If
TEMPs >TEMPSWITCH
then
If
TEMPs <=TEMPSWITCH
then
MELTP = 0
(11)
REFREZP = KF (TBASTEMPs)
If
TEMPs < TEMPSWITCH
then
(12)
If
TEMPs > = TEMPSWITCH
then
REFREZP = 0
TEMPSWITCH would be useful should future development of Object-GAWSER require dynam-
ic snowpack temperature data. Modeling multiple snowpack temperatures would be accomplished
by entering hourly snowpack temperature information as a graphical function in TBAS.
*Equations 710 are equivalent to equations A.2, A.5, A.9, and A.13 respectively from the GAWSER manual.
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