Simulation of New Zealand's climate using a high‐resolution nested regional climate model

Abstract

Abstract:A regional climate model (RCM) for New Zealand has been developed. The RCM is embedded within a GCM and both models are run under pre-industrial conditions. Seasonal mean output of the RCM is compared against NCEP data and the New Zealand national climate database. Regional and seasonal aspects of modelled surface temperature and precipitation are to a large extent simulated correctly. The main anomalies are related to the difficulty of incorporating New Zealand's orography appropriately and to the initial and lateral boundary conditions, which were supplied by the GCM. The largest anomalies occur over the Southern Alps, where the modelled temperatures are too low and where the amount of precipitation is too high. Many parts of the east coasts in both the North and South Island are too warm and too dry. Correlation patterns of temperature and precipitation with mean sea-level pressure differ considerably from the equivalent patterns constructed from NCEP data, but do show in general the dominant relationships between wind direction and temperature and precipitation.

Cloud effects on surface energy and mass balance in the ablation area of Brewster Glacier, New Zealand

“…during the last glacial maximum; Drost et al, 2007;Ackerley et al, 2011) may alter empirical relationships (i.e. TIMs) informed during the present climate, altering the climate signals derived from glacier fluctuations.…”

“…Given that this synoptic variability is closely linked to inferred changes in cloudiness as well as air mass properties (Hay and Fitzharris, 1988), and that these synoptic controls are thought to have varied over palaeoclimatic timescales (Drost et al, 2007;Ackerley et al, 2011), it is vital that the influence of clouds on SMB is separated out from the influence of air mass properties (in particular air temperature). Recent field studies on Brewster Glacier in the Southern Alps, have shown the high frequency of cloudy conditions during all seasons (> 50 % overcast conditions) as well as the significant and variable effect of clouds on SW↓, LW↓, and net radiation (Rnet) .…”

A method to encapsulate model structural uncertainty in ensemble projections of future climate: EPIC v1.0

“…The RCM domain spans 32 to 52 • S and 160 to 193 • E (167 • W) on a regular rotated grid with a horizontal resolution of 0.27 • and with the North Pole at 48 • N and 176 • E. Such a rotated grid, with the equator running through the New Zealand domain, ensures a quasi-uniform grid box spacing. The 0.27 • resolution results in a domain of 75 × 75 grid points, reduces computation time for long simulations, and has been shown to be adequate in previous studies (Drost et al, 2007). The spatial resolution necessitates a computational time step of 3 min.…”

“…to quantitatively establish the relationship between the change in annual mean global mean surface temperature and the change in the climate variable of interest and its variability. RCM simulations used in this study were performed using the Hadley Centre RCM HadRM3-PRECIS (Jones et al, 2004) that has been modified to be used for New Zealand (Bhaskaran et al, 1999(Bhaskaran et al, , 2002Drost et al, 2007) and which is described in further detail in Mullan et al (2016). The RCM domain spans 32 to 52 • S and 160 to 193 • E (167 • W) on a regular rotated grid with a horizontal resolution of 0.27 • and with the North Pole at 48 • N and 176 • E. Such a rotated grid, with the equator running through the New Zealand domain, ensures a quasi-uniform grid box spacing.…”

“…The spatial resolution necessitates a computational time step of 3 min. The model orography and vegetation data sets were updated from those used by Drost et al (2007) to the highresolution surface orography data set used in NIWA's operational forecast model (Ackerley et al, 2012); differences in the vegetation fields are small. The first year of model simulation (the spin-up) is excluded from the analysis, as this is used to achieve quasi-equilibrium conditions of the land surface and the overlying atmosphere.…”