A new, high-resolution climatological atmospheric dataset for southern New Zealand

Abstract

The regional climate of New Zealand’s South Island is shaped by the interaction of the Southern Hemisphere westerlies with the complex orography of the Southern Alps. Due to the geographical setting of New Zealand in the south-west Pacific, the properties of the transported air masses and the regional circulation itself are strongly influenced by the surrounding oceans. Therefore, variations in sea surface temperature (SST) are reflected on a variety of spatial and temporal scales and are statistically detectable through to temperature anomalies and glacier mass balance changes in the high mountains of the Southern Alps. The relationship between SST and high-mountain climate has not yet been investigated from a process perspective, leaving the underlying physical mechanisms that transmit large-scale SST signals to local climate anomalies and glacier mass changes unknown.We used dynamical downscaling with the Weather Research and Forecasting (WRF) model laterally forced by ERA5 reanalysis data to produce a regional atmospheric modeling dataset for the South Island of New Zealand. The dataset covers the present-day, 16-year period of 2005 to 2020. The high horizontal resolution of 2 km ensures that high-mountain topography and glaciers are resolved realistically, and convection is modeled explicitly. The two-domain setup is centered on Brewster Glacier, a benchmark glacier close to the main divide of the Southern Alps, which is the focus of further process-oriented investigations. The model configuration has been optimized to provide both reasonable output and fast simulation time, allowing for expense-limited follow-up sensitivity experiments.The dataset is evaluated regionally against an extensive network of observational meteorological data from the National Institute of Water and Atmospheric Research (NIWA) and MetService New Zealand as well as against atmospheric water content from Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. Locally, the model output is compared to high-mountain weather station measurements at Brewster Glacier. The model represents variability in both atmospheric water content and near-surface meteorological conditions generally well, although there are both seasonal and spatial biases that are particularly confined to high elevations. The local climate at Brewster Glacier (where landuse and topographic conditions have been optimized) is remarkably well represented on both seasonal and daily timescales.Given the fact that the Southern Hemisphere has been understudied in terms of multiscale climate and cryosphere relations, the dataset provides a unique and valuable tool for investigations of climate change and related impacts in southern New Zealand with high interdisciplinary relevance. Data from the finest-resolution model domain are available for download at daily temporal resolution from a public repository.