Air temperature variability in high-elevation glacierized regions: observations from six catchments on the Tibetan Plateau

Near-surface air temperature variability and the reliability of temperature extrapolation within glacierized regions are important issues for hydrological and glaciological studies that remain elusive because of the scarcity of high-elevation observations. Based on air temperature data in 2019 collected from 12 automatic weather stations, 43 temperature loggers and 6 national meteorological stations in six different catchments, this study presents air temperature variability in different glacierized/nonglacierized regions and assesses the robustness of different temperature extrapolations to reduce errors in melt estimation. The results show high spatial variability in temperature lapse rates (LRs) in different climatic contexts, with the steepest LRs located on the cold-dry northwestern Tibetan Plateau and the lowest LRs located on the warm-humid monsoonal-influenced southeastern Tibetan Plateau. Near-surface air temperatures in high-elevation glacierized regions of the western and central Tibetan Plateau are less influenced by katabatic winds and thus can be linearly extrapolated from off-glacier records. In contrast, the local katabatic winds prevailing on the temperate glaciers of the southeastern Tibetan Plateau exert pronounced cooling effects on the ambient air temperature, and thus, on-glacier air temperatures are significantly lower than that in elevation-equivalent nonglacierized regions. Consequently, linear temperature extrapolation from low-elevation nonglacierized stations may lead to as much as 40% overestimation of positive degree days, particularly with respect to large glaciers with a long flowline distances and significant cooling effects. These findings provide noteworthy evidence that the different LRs and relevant cooling effects on high-elevation glaciers under distinct climatic regimes should be carefully accounted for when estimating glacier melting on the Tibetan Plateau.

Weather & weather systems at Schirmacher Oasis (Maitri) during recent two decades - A review

Indian Antarctic station Maitri experiences varying external influences from interior of east Antarctica as well as moving depressions and cyclones along the coast. The relative position of circumpolar trough and strengthening of high pressure centre near pole influences variation of atmospheric pressure at Maitri. The diurnal, daily and seasonal variation of temperature mainly depend upon moving pressure systems, katabatic winds, change of solar insulation with change of seasons, reflectivity from clouds and snow surface. The katabatic winds prevail over Maitri which is highly directional from South- East sector due to increase of slope towards south. The blizzards are main weather at Maitri, fog and white out are occasional phenomena. The precipitation is mostly in form of snowfall but rain is very rare at Maitri. Heavy or moderate snowfall indicative of active front leading edge of warm air masses being transported southwards. Strong temperature variant near Schirmacher oasis give precipitation in form of snow. Fog occurred due to slow movement of relatively warm air from lower latitude over the colder surface. Winter season witnessed more snowfall accumulation at Maitri than other season. During summer rise of temperature accompanied with absorption of latent heat by ice pellets in low level of atmosphere results precipitation in form of water droplets. Highest number of blizzards occurs during winter season whereas lowest number of blizzards occurs during summer season. Normally due to cyclonic activities, warm air masses transported towards the Schirmacher oasis which causes rise of temperature at Maitri. Longer duration of the blizzards over the station depends upon strength of slow moving blocking anticyclone situated east of Maitri at lower latitude. Tremendous fluctuation of atmospheric electric field observed before onset is a pre-indication of commencement of blizzards.

Transit boosting of trans-Channel katabatic winds by depressions associated with west European storms tracks: impact on Pleistocene loess deposits.

Onshore and offshore sedimentological, geochemical, geomorphological, paleontological and geochronological studies of loess deposits located under and around the English Channel revealed that they were transported by katabatic winds generated by the British-Irish Ice Sheet. Katabatic winds, which are low-altitude wind flows, were able to jump over the low southern British hills but were stopped by the higher Brittany and Normandy hills. This regional topography is interrupted by a north-south corridor linking the northern and southern shores of Brittany where loess propagated down to the mouth of Loire River. This long transit shows that the total distance travelled by the katabatic wind was around 750 kilometres, which represents an unusual distance for the propagation of this wind under continental conditions. Strong similarities with Antarctica and Greenland, where well documented cases of katabatic winds are known, show that the transit of the trans-Channel katabatic winds were strongly enhanced by the seasonal drift of storms propagating in an eastward direction along the axis of the English Channel. This increasing strength of the North-South katabatic flux was probably at the origin of the transport of loess particles down to the mouth of Loire River.

The Irminger Sea – air-ice-ocean interactions in a 5 km coupled simulation with ICON-ESM

<p>Recent observations suggest that deep convection and water mass transformation in the Irminger Sea southeast of Greenland, together with overflows from the Nordic Seas, may be more important for the variability of the Atlantic meridional overturning circulation (AMOC) than the Labrador Sea. The preconditioning for and triggering of deep convection in the Irminger Sea is strongly associated with topography-induced mesoscale wind phenomena, such as Greenland tip jets, katabatic winds and marine cold air outbreaks. However, the resolution of current coupled climate models is too coarse to capture all the properties of these wind systems or to capture them at all. Here we explore the air-ice-ocean interactions induced by mesoscale wind phenomena in the Irminger Sea in a 1-year global coupled 5km simulation with ICON-ESM. The model is able to capture the complex interactions of the wind field and the ocean. We find that strong downward katabatic winds cause substantial heat loss from the Irminger Sea in addition to Greenland tip jets. The outflowing katabatic winds form narrow streaks of cold air that extend across the entire Irminger basin from southeast Greenland to Iceland. In addition, cold air outbreaks from the sea ice lead to the genesis of mesoscale cyclones, which in turn can cause Greenland tip jets before moving off to the east. All these wind phenomena cause substantial heat loss that preconditions the ocean for deep convection. If these wind systems are not resolved, the water mass transformation in the Irminger Sea could be too weak, contributing to why the Labrador Sea dominates AMOC variability in models. We conclude that resolving these mesoscale wind systems in an Earth system model could have significant implications for deep convection and water mass transformation in the Irminger Sea, and thus for AMOC variability.</p>

Mechanisms of slab avalanche release and impact in the Dyatlov Pass incident in 1959

The Dyatlov Pass incident is an intriguing unsolved mystery from the last century. In February 1959, a group of nine experienced Russian mountaineers perished during a difficult expedition in the northern Urals. A snow avalanche hypothesis was proposed, among other theories, but was found to be inconsistent with the evidence of a lower-than-usual slope angle, scarcity of avalanche signs, uncertainties about the trigger mechanism, and abnormal injuries of the victims. The challenge of explaining these observations has led us to a physical mechanism for a slab avalanche caused by progressive wind-blown snow accumulation on the slope above the hikers’ tent. Here we show how a combination of irregular topography, a cut made in the slope to install the tent and the subsequent deposition of snow induced by strong katabatic winds contributed after a suitable time to the slab release, which caused severe non-fatal injuries, in agreement with the autopsy results.

The Atmospheric Boundary Layer and Surface Conditions during Katabatic Wind Events over the Terra Nova Bay Polynya

Off the coast of Victoria Land, Antarctica an area of open water—the Terra Nova Bay Polynya (TNBP)—persists throughout the austral winter. The development of this coastal polynya is driven by extreme katabatic winds blowing down the slopes of Transantarctic Mountains. The surface-atmosphere coupling and ABL transformation during the katabatic wind events between 18 and 25 September 2012 in Terra Nova Bay are studied, using observations from Aerosonde unmanned aircraft system (UAS), numerical modeling results and Antarctic Weather Station (AWS) measurements. First, we analyze how the persistence and strength of the katabatic winds relate to sea level pressure (SLP) changes in the region throughout the studied period. Secondly, the polynya extent variations are analysed in relation to wind speed changes. We conclude that the intensity of the flow, surface conditions in the bay and regional SLP fluctuations are all interconnected and contribute to polynya development. We also analyse the Antarctic Mesoscale Prediction System (AMPS) forecast for the studied period and find out that incorrect representation of vertical ABL properties over the TNBP might be caused by overestimated sea ice concentrations (SIC) used as model input. Altogether, this research provides a unique description of TNBP development and its interactions with the atmosphere and katabatic winds.