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The effect of including Δρ in the bulk density model (ρsim) is illustrated in Figure 10(b). Due to the exceptionally large snow accumulation in January/February 1999 ρsim (without Δρ = diamond) overestimates the observed ρ. In contrast, when HN is included to model ρsim (stars) the bias decreases on 29 January and 6 February. Note that ρsim is not improved on days without new snow accumulation as the offset Δρ = 0. Still on 2 February 1999 (Figure 10(b)), the bias between ρ and ρsim is particularly large as a result of the above average HS during that period (see also Figure 6(a)). The extended bulk density model is used to compute ρsim and SWEsim of the stations where long-term records of HN are available (Table 4). The available time series of SWE at the seven stations are reduced to times where daily HN measurements are available. At the different locations, 31–43% of the available SWE data (n) was recorded during or shortly after snowfall (Table 4). In this table, nHN denotes the number of new snow events occurring in combination with manual SWE measurements. Whether HN or ΔHS is used to calculate Δρ, almost no differences in the results for ρsim and SWEsim are detected. At the stations Jochberg, Ginzling and Felbertauern, the application of HN leads to slightly better results but at Hinteriss, Boden and Obernberg the application of ΔHS results in slightly lower model errors. In Figure 11, the MAErel of the seven stations are evaluated applying the different modelling approaches. Starting with the approach used by Jonas et al. (2009) (Figure 11(a)), an adapted version of the Tyrol model with daily resolution (Figure 11(c)) is introduced using a quasi-monthly resolution (k and d of the 15th of a month (Figure 11(b)). Furthermore, the Tyrolean model with daily resolution is applied using an additional regional offset (Figure 11(d)) and the regional offset plus Δρ (Figure 11(e)).
Table 4

Metadata of seven stations providing long-term new snow data

StationElevation [m]RegionYearsnnHN
Hinterriß 930 1977–2009 473 172 
Jochberg 950 1971–2009 530 206 
Ginzling 1060 1977–2009 431 133 
Boden 1355 1977–2009 538 210 
Obernberg 1360 1977–2009 515 203 
Felbertauern 1650 1979–2009 517 217 
Kühtai 1930 1993–2009 373 162 
StationElevation [m]RegionYearsnnHN
Hinterriß 930 1977–2009 473 172 
Jochberg 950 1971–2009 530 206 
Ginzling 1060 1977–2009 431 133 
Boden 1355 1977–2009 538 210 
Obernberg 1360 1977–2009 515 203 
Felbertauern 1650 1979–2009 517 217 
Kühtai 1930 1993–2009 373 162 

n, the number of records; nHN, the number of SWE measurements which are influenced by new snow.

Figure 11

Relative errors (MAErel) for SWE at seven stations providing long-term new snow data. The comparison includes (a) model by Jonas et al. (2009), (b) Tyrol monthly resolution, (c) Tyrol daily resolution, (d) Tyrol daily resolution with regional offset OSreg and (e) Tyrol daily resolution with regional offset OSreg and new snow correction Δρ.

Figure 11

Relative errors (MAErel) for SWE at seven stations providing long-term new snow data. The comparison includes (a) model by Jonas et al. (2009), (b) Tyrol monthly resolution, (c) Tyrol daily resolution, (d) Tyrol daily resolution with regional offset OSreg and (e) Tyrol daily resolution with regional offset OSreg and new snow correction Δρ.

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