Articles | Volume 8, issue 4
Earth Syst. Dynam., 8, 1247–1261, 2017

Special issue: The 8th EGU Leonardo Conference: From evaporation to precipitation:...

Earth Syst. Dynam., 8, 1247–1261, 2017

Research article 22 Dec 2017

Research article | 22 Dec 2017

Evaluation of the moisture sources in two extreme landfalling atmospheric river events using an Eulerian WRF tracers tool

Jorge Eiras-Barca1, Francina Dominguez2, Huancui Hu2, Daniel Garaboa-Paz1, and Gonzalo Miguez-Macho1 Jorge Eiras-Barca et al.
  • 1Non-Linear Physics Group, Universidade de Santiago de Compostela, Galicia, Spain
  • 2Department of Atmospheric Sciences, University of Illinois at Urbana–Champaign, Urbana–Champaign, IL, USA

Abstract. A new 3-D tracer tool is coupled to the WRF model to analyze the origin of the moisture in two extreme atmospheric river (AR) events: the so-called Great Coastal Gale of 2007 in the Pacific Ocean and the Great Storm of 1987 in the North Atlantic. Results show that between 80 and 90 % of moisture advected by the ARs, and a high percentage of the total precipitation produced by the systems have a tropical origin. The tropical contribution to precipitation is in general above 50 % and largely exceeds this value in the most affected areas. Local convergence transport is responsible for the remaining moisture and precipitation. The ratio of tropical moisture to total moisture is maximized as the cold front arrives on land. Vertical cross sections of the moisture content suggest that the maximum in tropical humidity does not necessarily coincide with the low-level jet (LLJ) of the extratropical cyclone. Instead, the amount of tropical humidity is maximized in the lowest atmospheric level in southern latitudes and can be located above, below or ahead of the LLJ in northern latitudes in both analyzed cases.

Short summary
This paper analyzes the origin of the moisture in two extremely important atmospheric river (and extreme precipitation) events. The distribution of the moisture with regard to the low-level jet is analyzed as well, and the classic association of the atmospheric river to the former is discussed.
Final-revised paper