Winter (DJF) temperature and precipitation variability in an Arctic Archipelago, Svalbard is investigated for an extreme event during December 2015 as well as on interannual time scales. During December 2015–16, a strong high pressure anomaly over northern Europe channelised warm and moist air into Ny Ålesund (∼79°N and ∼11°E) resulting in extreme temperature and precipitation. This high pressure anomaly was a result of wave trains associated with the Madden Julian Oscillation (MJO). On interannual time scales, the observation site, Ny Ålesund was characterised by an increasing trend in precipitation and temperature. A composite of SLP anomalies associated with the temperature and precipitation anomalies was characterised by a high pressure anomaly over northern Europe. The second mode in the EOF of SLP anomalies during winter (DJF) also indicated the presence of a high pressure anomaly over northern Europe, extending into the Pacific. The mode was correlated significantly with the ENSO. During the study period, more than 50% of the ENSO events influenced temperature and precipitation in Ny Alesund. In the present study, the EOF-2 temporal pattern correlated strongly with La Nina in the Pacific, suggesting the generation of a high/low pressure anomaly during negative/positive ENSO phases. On interannual timescales, extremes were conspicuous, particularly when La Nina coincided with active MJO. This may be due to the fact that both processes generate similar pressure anomalies in northern Europe and reinforce each other. This study also suggests that the influence of El Nino is weaker than La Nina. It is also noted that decadal oscillations in the Pacific, particularly the Interdecadal Pacific Oscillation (IPO) also enhance the high-pressure anomalies over northern Europe. Thus, the temperature and precipitation in a high Arctic location, Ny Ålesund is interconnected, at least hemispherically and is defined by processes of different time scales.

Clouds play a significant role in regulating the Arctic climate and water cycle due to their impacts on radiative balance through various complex feedback processes. However, there are still large discrepancies in satellite and numerical model-derived cloud datasets over the Arctic region due to a lack of observations. Here, we report observations of cloud base height (CBH) characteristics measured using a Vaisala CL51 ceilometer at Ny-Ålesund, Svalbard. The study highlights the monthly and seasonal CBH characteristics at the location. It is found that almost 40% of the lowest CBHs fall within a height range of 0.5–1 km. The second and third cloud bases that could be detected by the ceilometer are mostly concentrated below 3 km during summer but possess more vertical spread during the winter season. Thin and low-level clouds appear to be dominant during the summer. Low-level clouds are found to be dominant and observed in 76% of cases. The mid and high-level clouds occur in ~16% and ~7% of cases, respectively. Further, micro rain radar (MRR2) observed enhanced precipitation and snowfall events during the winter and spring which are found to be associated with the lowest CBHs within 2 km from the ground. The frontal process associated with synoptic-scale meteorological conditions explains the variabilities in CBH and precipitation at the observation site when compared for two contrasting winter precipitation events. The findings of the study could be useful for model evaluation of cloud precipitation relationships and satellite data validation in the Arctic environment.

Antarctic Circum Polar Wave (ACW) do not propagate in the Indian Ocean RegionTopographic meandering of ACC decouples ocean-atmosphere coupled ACWVertical/meridional temperature advection overwhelms zonal advection

Hails observed at Ny Alesund, Svalbard in the Arctic during December–February 2018–19 is examined along with the atmospheric circulation patterns. When hail was noticed, surface warming and southwesterly—westerly winds were noticed. Atmospheric circulation pattern was characterised by high pressure anomaly over northwestern Europe. High clouds as well as excess liquid water were present when the high pressure systems were active over northwestern Europe. This is because winds blowing over ocean collect more moisture as well as transport nucleating particles to Svalbard. Also, hourly winds from ERA 5 reanalysis indicated vertical shear required for hail formation. When hails were observed, mixed precipitation types were recorded with the maximum intensities arising from the hails. The West Spitzbergen Current (WSC) induces a strong east west sea surface temperature (SST) gradient in the ocean west of Svalbard. A corresponding gradient in the atmospheric temperature is also maintained by the WSC in the west to east direction in the lower atmosphere. Moisture laden westerlies cross the SST gradient and induce strong frontal activity in the lower atmosphere resulting intense precipitation and hail. The upward vertical velocity noted in the lower troposphere supports the frontal activity. Human activities in the Arctic as elsewhere are bound to increase. Hence, there is a need to study the intense precipitation in the Arctic as well as its reasons as it can impact the Arctic environment and human activity. This calls for more continuous observations to clearly identify mechanisms and frequency of intense precipitation in the Arctic.

The mechanisms behind Arctic warming and associated climate changes are difficult to discern. Also, the complex local processes and feedbacks like aerosol-cloud-climate interactions are yet to be quantified. Here, using the Community Earth System Model (CAM5) experiments, with emission enhancement of anthropogenic sulfate 1) five-fold globally, 2) ten-times over Asia, and 3) ten-times over Europe we show that regional emissions of sulfate aerosols alter seasonal warming over the Arctic, i.e., colder summer and warmer winter. European emissions play a dominant role in cooling during the summer season (0.7 K), while Asian emissions dominate the warming during the winter season (maximum ∼0.6 K) in the Arctic surface. The cooling/warming is associated with a negative/positive cloud radiative forcing. During the summer season increase in low–mid level clouds, induced by sulfate emissions, favours the solar dimming effect that reduces the downwelling radiation to the surface and thus leads to surface cooling. Warmer winters are associated with enhanced high-level clouds that induce a positive radiative forcing at the top of the atmosphere. This study points to the importance of international strategies being implemented to control sulfate emissions to combat air pollution. Such strategies will also affect the Arctic cooling/warming associated with a cloud radiative forcing caused by sulfate emission change.