ABSTRACT. Multi-annual records of glacier surface meteorology and energy balance are necessary to resolve glacier-climate interactions but remain sparse, especially in the Southern Hemisphere. To address this, we present a record from the ablation zone of Brewster Glacier, New Zealand, between October 2010 and September 2012. The mean air temperature was 1.2°C at 1760 m a.s.l., with only a moderate temperature difference between the warmest and coldest months (�8°C). Long-term annual precipitation was estimated to exceed 6000 mm a -1 , with the majority of precipitation falling within a few degrees of the freezing level. The main melt season was between November and March (83% of annual ablation), but melt events occurred during all months. Annually, net radiation was positive (a source of energy) and supplied 64% of the melt energy, driven primarily by net shortwave radiation. Net longwave radiation was often positive during cloudy conditions in summer, demonstrating the radiative importance of clouds during melt. Turbulent sensible and latent heat fluxes were directed towards the surface in the summer months, accounting for just over a third of the energy for melt (34%). The energy gain associated with rainfall was small except during heavy events in summer.

The turbulent sensible and latent heat fluxes are important components of the surface energy balance over glaciers in the Southern Alps of New Zealand, contributing over half the energy available for ablation during large melt events. To calculate these terms confidently in glacier mass-balance models it is essential to use appropriate parameterizations for surface roughness and atmospheric stability. Eddy covariance measurements at Brewster Glacier were obtained over an ice surface to help facilitate an assessment of the calculation of the turbulent heat fluxes. The roughness length for momentum was found to be 3.6 x 10−3m, while the roughness lengths for temperature and humidity were two orders of magnitude smaller, in agreement with surface renewal theory. A Monte Carlo approach was used to assess the uncertainty in turbulent heat fluxes calculated using the bulk aerodynamic method. It was found that input-data and roughness-length uncertainty could not explain underestimates of observed sensible heat fluxes during periods with low wind speed and large temperature gradients. During these periods a katabatic wind speed maximum alters the formulation of the turbulent exchange coefficient to that typically observed in a neutral atmosphere and this has implications for glacier mass-balance sensitivity.

ABSTRACT. Recognising the scarcity of glacier mass-balance data in the Southern Hemisphere, a massbalance measurement programme was started at Brewster Glacier in the Southern Alps of New Zealand in 2004. Evolution of the measurement regime over the 11 years of data recorded means there are differences in the spatial density of data obtained. To ensure the temporal integrity of the dataset a new geostatistical approach is developed to calculate mass balance. Spatial co-variance between elevation and snow depth allows a digital elevation model to be used in a co-kriging approach to develop a snow depth index (SDI). By capturing the observed spatial variability in snow depth, the SDI is a more reliable predictor than elevation and is used to adjust each year of measurements consistently despite variability in sampling spatial density. The SDI also resolves the spatial structure of summer balance better than elevation. Co-kriging is used again to spatially interpolate a derived mean summer balance index using SDI as a co-variate, which yields a spatial predictor for summer balance. The average glacier-wide surface winter, summer and annual balances over the period 2005-15 are 2484, −2586 and −102 mm w.e., respectively, with changes in summer balance explaining most of the variability in annual balance.

Abstract. In New Zealand, direct measurements of mass balance are sparse due to the inaccessibility of glaciers in the Southern Alps and the logistical difficulties associated with maintaining a mass balance record. In order to explore the benefit of remotely sensed imaging to monitor mass balance in the Southern Alps, this research assesses the relationship between measurements of glacier surface albedo derived from Moderate Resolution Imaging Spectroradiometer (MODIS) and mass balance observations using the glaciological method on Brewster Glacier over the 2005-2013 period. We confirm that minimum glacier-wide albedo is a reliable predictor for annual mass balance in this maritime environment (R 2 = 0.93). Furthermore, we show that regular monitoring of glacier-wide albedo enables a new metric of winter accumulation to be derived, namely the cumulative winter albedo, which is found to correlate strongly with winter mass balance (R 2 = 0.88), thus enabling the reconstruction of separate winter and summer mass balance records. This allows the mass balance record for Brewster Glacier to be extended back to the start of MODIS observations in 2000 and to confirm that the annual balance of Brewster Glacier is largely controlled by summer balance (R 2 = 92 %). An application of the extended record is proposed whereby the relationship between mass balance and the photographic record of the end-of-summer snowline altitude is assessed. This allowed the annual balance record of Brewster Glacier to be reconstructed over the period 1977-2013, thus providing the longest record of mass balance for a glacier in New Zealand.Over the 37-year period, our results show that Brewster Glacier gained a significant mass of up to 14.5 ± 2.7 m w.e. by 2007. This gain was offset by a marked shift toward negative balances after 2008, yielding a loss of 5.1 ± 1.2 m w.e., or 35 % of the gain accumulated over the previous 30 years. The good correspondence between mass balance of Brewster Glacier and the phase of the Pacific (Inter-)Decadal Oscillation (PDO/IPO), associated with the fast terminus retreat observed between 1978 and 1998, strongly suggests that the observed mass gain of Brewster Glacier since 1977 is only offsetting a longer sequence of dominantly negative balances.

ABSTRACT:Clouds are important features of many high-altitude and glaciated areas, yet detecting their presence and specifying their effects on incoming shortwave (SW↓), longwave (LW↓) and net all-wave radiation (Rnet) remains challenging in these environments. These limitations hamper efforts to understand atmospheric controls on glacier surface mass balance (SMB) in the Southern Alps of New Zealand, as both cloud and airmass forcing accompanies key synoptic controls on SMB. Multi-year datasets of four-component broadband radiation from two sites at Brewster Glacier, Southern Alps of New Zealand, are used here to develop cloud metrics to account for the effects of clouds on SW↓, LW↓ and Rnet. On average 23% of top-of-atmosphere shortwave radiation (SW TOA ) is attenuated by the clear-sky atmosphere, while clouds attenuate a further 31%, resulting in <50% of SW TOA being received at the surface. The transmission of shortwave radiation by clouds (trc) during overcast conditions is found to vary with season and airmass characteristics. A simple parameterization is developed to account for lower trc observed during periods of higher water vapour pressure. Cloud metrics derived at the site show overcast conditions are frequent (45% of period) and strongly dependent on wind direction, highlighting the dominant role of orography in cloud formation and enhancement in the Southern Alps. The effect of clouds on Rnet exhibits a distinct seasonal variation; during summer when albedo and trc are lower, clouds decrease Rnet by 20-40 W m −2 , while during autumn, winter and spring, clouds enhance Rnet by approximately 20 W m −2 . Idealized modelling shows that these patterns are strongly dependent on albedo and extend across the elevation range of glaciers in the Southern Alps. Thus, overcast conditions appear to aid the extension of ablation into spring and autumn by increasing the energy available for snow and ice melt.

Abstract. The effect of clouds on glacier surface energy balance (SEB) has received increased attention in the last decade, but how clouds interact with other meteorological forcing to influence surface mass balance (SMB) is not as well understood. This paper resolves the SEB and SMB at a site in the ablation zone of Brewster Glacier over a 22-month period, using high-quality radiation data to carefully evaluate SEB terms and define clear-sky and overcast conditions. A fundamental change in glacier SEB in cloudy conditions was driven by increased effective sky emissivity and surface vapour pressure, rather than a minimal change in air temperature and wind speed. During overcast conditions, positive net long-wave radiation and latent heat fluxes allowed melt to be maintained through a much greater length of time compared to clear-sky conditions, and led to similar melt in each sky condition. The sensitivity of SMB to changes in air temperature was greatly enhanced in overcast compared to clear-sky conditions due to more frequent melt and changes in precipitation phase that created a strong albedo feedback. During the spring and autumn seasons, the sensitivity during overcast conditions was strongest. To capture these processes, future attempts to explore glacier-climate interactions should aim to resolve the effects of atmospheric moisture (vapour, cloud, and precipitation) on melt as well as accumulation, through enhanced statistical or physically based methods.

The occurrence of extreme precipitation events in New Zealand regularly results in devastating impacts to the local society and environment. An automated atmospheric river (AR) detection technique (ARDT) is applied to construct a climatology (1979-2019) of extreme mid-latitude moisture fluxes conducive to extreme precipitation. A distinct seasonality exists in AR occurrence aligning with seasonal variations in the mid-latitude jet streams. The formation of the Southern Hemisphere winter split jet enablesARoccurrence to persist through all seasons in northern regions of New Zealand, while southern regions of the country exhibit a substantial (50%) reduction in AR occurrence as the polar jet shifts southward during the cold season. ARs making landfall on the western coast of New Zealand (90% of all events) are characterised by a dominant north-westerly moisture flux associated with a distinct dipole pressure anomaly; low pressure to the south-west and high pressure to the north-east of New Zealand. Precipitation totals during AR events increases with AR rank (five-point scale) throughout the country, with the most substantial increase on the windward side of the Southern Alps (South Island), with the largest events (rank 5 ARs) producing 3-day precipitation totals exceeding 1000 mm. ARs account for up to 78% of total precipitation and up to 94% of extreme precipitation on the West Coast of the South Island. Assessment of the multi-scale atmospheric processes associated with AR events governing extreme precipitation in the Southern Alps of New Zealand should remain a priority given their hydrological significance and impact on people and infrastructure.

Meteorological and glaciological data obtained over an intensive 2 year measurement period (2000)(2001)(2002) are used to run a physically based climatic mass balance model to characterize a seasonal variability in mass and energy exchanges at Summit, Greenland. The model resolves the full surface energy balance and the subsurface temperature profile by inclusion of energy release from penetrating shortwave radiation. A Monte Carlo approach using 1000 different parameter combinations is adopted to assess model uncertainty, with output compared to measured surface and subsurface temperatures, changes in surface height, and eddy correlation data. The heat exchanges associated with the change in phase of water are very small in all seasons, with the average turbulent latent heat flux equal to 0.4 (±0.2) W m À2 . This suggests that the mean annual water vapor gradient is toward the surface, resulting in a mass gain of 4.1 mm WE yr À1 . The mass gain represents only a small fraction of the total accumulation (<2%), in part because of the change in sign of the water vapor flux from winter (deposition) to summer (sublimation), but if assumed to be typical of the entire dry snow zone (40% of the total ice sheet area) is equivalent to approximately 5.5 Gt yr À1 . A simple experiment based on 2012 atmospheric conditions suggests that mass turnover from water vapor exchanges will likely be enhanced in a warming climate, with sublimation increasing more than deposition. Should the sign of the mean turbulent latent heat flux change due to warming, the present mass gain in the dry snow zone could easily become a mass loss of equal proportion, which would further enhance the negative mass balance of the Greenland ice sheet.