Impact of land surface conditions on 2004 North American monsoon in GCM experiments

• Published in: Journal of geophysical research. Atmospheres 2013-01, Vol.118 (2), p.293-305
• Main Authors: Feng, X., Bosilovich, M., Houser, P., Chern, J.-D.
• Format: Article
• Language: English
• Subjects: Atmospheric circulation; Boundary layers; Bowen ratio; Convection; Data collection; Earth, ocean, space; Exact sciences and technology; External geophysics; Fluctuations; General circulation models; Geophysics; land surface impact; Latent heat; Meteorology; Moisture content; Monsoons; North American monsoon; Recycling; Sensible heat; Soil moisture; soil moisture-precipitation feedback; Surface temperature
• ISSN: 2169-897X; 2169-8996
• DOI: 10.1029/2012JD018805

In this study, two sets of six‐member ensemble simulations were performed for the boreal summer of 2004 using the Finite Volume General Circulation model to investigate the sensitivity of the North American monsoon (NAM) system to land surface conditions and further to identify the mechanisms by which land surface processes control the NAM precipitation. The control simulation uses a fully interactive land surface model, whereas the sensitivity experiment uses prescribed land surface fields from the Global Land Data Assimilation System.The response of the monsoon precipitation to land surface changes varies over different regions modulated by two different soil moisture–precipitation feedbacks. The vast northern NAM region, including most of Arizona and New Mexico, as well as the northwestern Mexico shows that soil moisture has a positive feedback with precipitation primarily due to local recycling mechanisms. The reduction of soil moisture decreases latent heat flux and increases sensible heat flux and consequently increases the Bowen ratio and surface temperature, leading to a deep (warm and dry) boundary layer, which suppresses convection and hence reduces precipitation. Over the west coast of Mexico near Sinaloa, a negative soil moisture–precipitation relationship is noted to be associated with a large‐scale mechanism. The reduced soil moisture changes surface fluxes and hence boundary layer instability and ultimately low‐level circulation. As a result, the changes in surface pressure and large scale wind field increase moisture flux convergence and consequently moisture content, leading to increased atmospheric instability and in turn enhancing convection and accordingly precipitation. These results further reinforce the important role of land surface conditions on surface process, boundary structure, atmospheric circulation, and rainfall during the NAM development. Key Points Identify land surface impact on the North American monsoon (NAM) A positive soil moisture‐precipitation feedback due to local recycling mechanism A negative soil moisture‐precipitation feedback due to large-scale mechanism