calculating air pressure in high altitude cold lakes

[OlssonF]

I was trying to run LER at Toolik Lake in Alaska (elevation 715 m) using GOTM and Simstrat. In format_met() it was returning NAs in the GOTM met file and NaN in the p_air in simstrat.par. There's a bit where it calculates air pressure from a number of constants and air temperature (I think), but returns NaN when the elevation is 715 m (as Toolik is), when the temperature is set to 4 oC which it is.
Here is the code chunk in question:

if (!chck_met$p_surf) {
        g <- 9.80665
        Pb <- 101325
        Lb <- -0.0065
        R <- 8.31432
        M <- 0.0289644
        at_samp <- met[[l_names$airt]]
        at_samp[at_samp < 4] <- 4
        met[[l_names$p_surf]] <- Pb * (1 + (Lb/at_samp) * (elev))^((-g * 
            M)/R * Lb)
        chck_met$p_surf <- TRUE
    }

And this is the code I ran to investigate

g <- 9.80665
Pb <- 101325
Lb <- -0.0065
R <- 8.31432
M <- 0.0289644
elev <- 715

at_samp<- 4

Pb * (1 + (Lb/at_samp) * (elev))^((-g * M)/R * Lb)

It seems that any elevation above 615 m causes this error.

[robertladwig]

Super interesting find! Yes, as long as elevation is < than -at_samp/Lb it works, so the threshold for this function is 615.3846 m. Seems this originates from some empirical function that didn't had any data with higher elevations included.