Atmospheric moisture transport and its role in the Arctic hydrological cycle and snow cover

Considerably higher rate of temperature increase in the northern high latitudes compared to the Northern Hemisphere and the globe is one of the most important and intriguing features of the ongoing global warming. The strong warming is accompanied by unprecedented loss of the Arctic sea ice cover, which has considerably accelerated in the last five years and is now far beyond the trends predicted by global climate models. In the attempts to understand and explain the observed Arctic warming the major arguments go along the interplay of the external climate forcing (mostly anthropogenic greenhouse gases) and the internal natural variability which may both contribute to the recent accelerating climate changes in the northern high latitudes. If the observed temperature and sea ice trends are externally driven, the projections of climate models based on anthropogenic forcing concept do provide rather reliable estimates of climate change in the next decades of the 21st century. Alternatively, if, the internal climate fluctuations play the major role, the uncertainty of model predictions would considerably increase and will be dependent on the nature of these internal fluctuation. In the case of considerable contribution of the internal processes, we can expect the mitigation of the warming and returning back to the relatively cooler climate state.

Arctic hydrolological cycle plays a critical and still poorly understood role in this paradigm. First of all, the major source terms (precipitation, evaporation, advective transport) of the Arctic hydrological cycle are poorly quantified in observations and parameterized in the models with high uncertainties. As a result, Arctic climate feedbacks, first all engaging moisture-related ones have large uncertainties with sometimes their signs being undetermined. One of the most uncertain components of the Arctic hydrological cycle is Arctic precipitation in general and its component associated with solid precipitation in particular. Under low temperatures solid state precipitation and liquid precipitation are alternating each other contributing very differently to the surface and ground water storage.

To establish a better understanding of the mechanisms forming Arctic hydrological cycle and its role in the Arctic climate predictability we propose to analyse the role of atmospheric moisture transport in the Arctic hydrological cycle using two concepts. First, we will employ an Eulerian approach in which the moisture transports are directly estimated using high resolution grids from modern era reanalyses (for present climate) and CMIP5 climate model runs with a particular emphasis on French climate community models (for climate projections). In the second concept we will apply Lagrangian approach in which local moisture budgets are associated with remote sources of moisture. In the first approach we will obtain estimates of variability of moisture transports for different Arctic domains and the second approach will allow for association of the local hydrological budgets with moisture sources originating from the Atlantic Ocean and surrounding continents. Synergizing the two types of estimates we will associate the observed and projected changes in the Arctic moisture transports with high latitudinal cyclone activity and its role in forming Arctic hydrological budgets on different time scales. In particular, we are very much hopeful to discriminate the role of the local and remote moisture sources and to quantify the role of local evaporation (increasing under the ice decline) and advection of moisture (including abrupt anomalous advective events associated with atmospheric rivers) in forming the Arctic atmospheric moisture budgets.

Quantifying transport of moisture and its impact on atmospheric water content in the Arctic we also hope to establish more truth in tendencies in the amount of solid precipitation in the Arctic region and associated snow cover and snow depth characteristics. The latter exhibits a clear clustering over the last decades with show cover area at least over the Northern Eurasia declining, but the snow depth and accumulation significantly growing up in many regions. A challenging this is to associate these signals with the character of high-latitudinal precipitation and its sources linked to the moisture advection.

Being armed with above mentioned estimates we will analyse moisture-related climate feedbacks in the Arctic and sensitivity of the key-elements of the Arctic climate system to the sources of atmospheric moisture. This will allow for understanding the mechanisms of predictability of Arctic climate at different time scales and potentially for discriminating the role of external forcing and natural variability in the observed Arctic climate change.