Interannual variability of Greenland winter precipitation sources: Lagrangian moisture diagnostic and North Atlantic Oscillation influence

Abstract

[1] We present a new Lagrangian diagnostic for identifying the sources of water vapor for precipitation. Unlike previous studies, the method allows for a quantitative demarcation of evaporative moisture sources. This is achieved by taking into account the temporal sequence of evaporation into and precipitation from an air parcel during transport, as well as information on its proximity to the boundary layer. The moisture source region diagnostic was applied to trace the origin of water vapor for winter precipitation over the Greenland ice sheet for 30 selected months with pronounced positive, negative, and neutral North Atlantic Oscillation (NAO) index, using the European Centre for Medium-Range Weather Forecasts' ERA-40 reanalysis data. The North Atlantic and the Nordic seas proved to be the by far dominant moisture sources for Greenland. The location of the identified moisture sources in the North Atlantic basin strongly varied with the NAO phase. More specifically, the method diagnosed a shift from sources north of Iceland during NAO positive months to a maximum in the southeastern North Atlantic for NAO negative months, qualitatively consistent with changes in the concurrent large-scale mean flow. More long-range moisture transport was identified during the NAO negative phase, leading to the advection of moisture from more southerly locations. Different regions of the Greenland ice sheet experience differing changes in the average moisture source locations; variability was largest in the north and west of Greenland. The strong moisture source variability for Greenland winter precipitation with the NAO found here can have a large impact on the stable isotope composition of Greenland precipitation and hence can be important for the interpretation of stable isotope data from ice cores. In a companion paper, the implications of the present results are further explored in that respect.

Atmospheric processes triggering the central European floods in June 2013

“…The intensity of these uptakes preceding the precipitation is reduced since they contribute less to the moisture arriving in the area of interest. This procedure is explained in detail in Sodemann et al (2008), and has been applied successfully in several previous studies, for example, Sodemann and Zubler (2010), Winschall et al (2012Winschall et al ( , 2014.…”

“…Evaporative moisture sources of the precipitation event are calculated with the Lagrangian technique developed by Sodemann et al (2008). This technique considers 6-hourly changes of specific humidity q along backward trajectories from the considered area of precipitation and attributes positive changes of q with time to local moisture uptake due to surface evaporation.…”

Oceanic sources of continental precipitation and the correlation with sea surface temperature

“…This is always an arbitrary choice, and most studies have chosen it in terms of a certain flux but did not provide information on how much moisture the area within a boundary receives as a percentage of the source region's evaporation (forward tracking) or precipitation (backward tracking) [e.g., Sodemann et al, 2008;Dirmeyer et al, 2009a ;Dominguez et al, 2009 ;Drumond et al, 2010 ;Gimeno et al, 2010]. We like to argue that this information is crucial in assessing the spatial extent of a source region's influence.…”

“…[4] Many of these atmospheric moisture tracking studies focused on a particular basin, country, or terrestrial region and identified the moisture sources or sinks for that region taking account of interannual or seasonal variability [e.g., Druyan and Koster, 1989;Numaguti, 1999;Yoshimura et al, 2004;Bosilovich and Chern, 2006;Nieto et al, 2006;Sodemann et al, 2008;Dominguez et al, 2009;Drumond et al, 2010;Gangoiti et al, 2011aGangoiti et al, , 2011bBagley et al, 2012;Keys et al, 2012;Tuinenburg et al, 2012]. More global characterizations of moisture sources showed the import and export of water vapor between nations [Dirmeyer et al, 2009a], or the oceanic versus terrestrial contributions to continental precipitation [e.g., van der Ent et al, 2010;Goessling and Reick, 2011] [5] Our own recent work [van der Ent et al, 2010;van der Ent and Savenije, 2011] showed that globally about 40% of the precipitation on land originates from continental rather than oceanic evaporation.…”

Seasonal and inter‐annual variability of the moisture sources for Alpine precipitation during 1995–2002

“…Hereby, the aim is to identify the leading moisture source regions for Alpine precipitation and to quantify their seasonal and inter-annual variability. The moisture sources are diagnosed from European Centre for Medium-Range Weather Forecasts (ECMWF) ERA-40 reanalysis data, using the quantitative Lagrangian moisture source diagnostic by Sodemann et al (2008b). The use of a diagnostic method, as opposed for example to general circulation model simulations, has two advantages.…”