Evaluating the influence of antecedent soil moisture on variability of the North American monsoon precipitation in the Coupled MM5/VIC Modeling System

Abstract This work examines the effect of horizontal resolution and topography on the North American monsoon (NAM) in experiments with an atmospheric general circulation model. Observations are used to evaluate the fidelity of the representation of the monsoon in simulations from the Community Atmosphere Model version 5 (CAM5) with a standard 1.0° grid spacing and a high-resolution 0.25° grid spacing. The simulated monsoon has some realistic features, but both configurations also show precipitation biases. The default 1.0° grid spacing configuration simulates a monsoon with an annual cycle and intensity of precipitation within the observational range, but the monsoon begins and ends too gradually and does not reach far enough north. This study shows that the improved representation of topography in the high-resolution (0.25° grid spacing) configuration improves the regional circulation and therefore some aspects of the simulated monsoon compared to the 1.0° counterpart. At higher resolution, CAM5 simulates a stronger low pressure center over the American Southwest, with more realistic low-level wind flow than in the 1.0° configuration. As a result, the monsoon precipitation increases as does the amplitude of the annual cycle of precipitation. A moisture analysis sheds light on the monsoon dynamics, indicating that changes in the advection of enthalpy and moist static energy drive the differences between monsoon precipitation in CAM5 1.0° compared to the 0.25° configuration. Additional simulations confirm that these improvements are mainly due to the topographic influence on the low-level flow through the Gulf of California, and not only the increase in horizontal resolution.

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Effects of Initial Soil Moisture on Rainfall Generation and Subsequent Hydrologic Response during the North American Monsoon

Journal of Hydrometeorology ◽

10.1175/2008jhm1069.1 ◽

2009 ◽

Vol 10 (3) ◽

pp. 644-664 ◽

Cited By ~ 43

Author(s):

Enrique R. Vivoni ◽

Kinwai Tai ◽

David J. Gochis

Keyword(s):

Soil Moisture ◽

North American ◽

Initial Conditions ◽

Hydrologic Model ◽

North American Monsoon ◽

Meteorological Model ◽

Initial Soil Moisture ◽

The North ◽

Spatial Coverage ◽

Initial Soil

Abstract Through the use of a mesoscale meteorological model and distributed hydrologic model, the effects of initial soil moisture on rainfall generation, streamflow, and evapotranspiration during the North American monsoon are examined. A collection of atmospheric fields is simulated by varying initial soil moisture in the meteorological model. Analysis of the simulated rainfall fields shows that the total rainfall, intensity, and spatial coverage increase with higher soil moisture. Hydrologic simulations forced by the meteorological fields are performed using two scenarios: (i) fixed soil moisture initializations obtained via a drainage experiment in the hydrologic model and (ii) adjusted initializations to match conditions in the two models. The scenarios indicate that the runoff ratio increases with higher rainfall, although a change is observed from a linear (fixed initialization) to a nonlinear response (adjusted initialization). Variations in basin response are attributed to controls exerted by rainfall, soil, and vegetation properties for varying initial conditions. Antecedent wetness significantly influences the runoff response through the interplay of different runoff generation mechanisms and also controls the evapotranspiration process. The authors conclude that a regional increase in initial soil moisture promotes rainfall generation, streamflow, and evapotranspiration for this warm-season case study.

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Precipitation Recycling Variability and Ecoclimatological Stability—A Study Using NARR Data. Part II: North American Monsoon Region

Journal of Climate ◽

10.1175/2008jcli1760.1 ◽

2008 ◽

Vol 21 (20) ◽

pp. 5187-5203 ◽

Cited By ~ 86

Author(s):

Francina Dominguez ◽

Praveen Kumar ◽

Enrique R. Vivoni

Keyword(s):

Soil Moisture ◽

North American ◽

Large Scale ◽

Singular Spectrum Analysis ◽

Feedback Mechanism ◽

North American Monsoon ◽

Monsoon Precipitation ◽

Subsequent Increase ◽

Seasonally Dry ◽

Precipitation Recycling

Abstract This work studies precipitation recycling as part of the dynamic North American monsoon system (NAMS) to understand how moisture and energy fluxes modulate recycling variability at the daily-to-intraseasonal time scale. A set of land–atmosphere variables derived from North American Regional Reanalysis (NARR) data are used to represent the hydroclimatology of the monsoon. The recycling ratio is estimated using the Dynamic Recycling Model, which provides recycling estimates at the daily time scales. Multichannel singular spectrum analysis (M-SSA) is used to extract trends in the data while at the same time selecting only the variability common to all of the variables. The 1985–2006 climatological analysis of NAMS precipitation recycling reveals a positive feedback mechanism between monsoon precipitation and subsequent increase in precipitation of recycled origin. Recycling ratios during the monsoon are consistently above 15% and can be as high as 25%. While monsoon precipitation and evapotranspiration are predominantly located in the seasonally dry tropical forests in the southwestern part of the domain, recycling is enhanced northeast of this region, indicating a relocation of soil moisture farther inland to drier regions in the northeast. The three years with the longest monsoons in the 22-yr period present an asynchronous pattern between precipitation and recycling ratio. The longest monsoons have a characteristic double peak in precipitation, with enhanced recycling ratios during the intermediate dry period. This indicates that, even when large-scale moisture advection decreases, evapotranspiration provides moisture to the overlying atmosphere, contributing to precipitation. Through the negative feedback present during long monsoons and by relocation of soil moisture, precipitation recycling brings favorable conditions for vegetation sustenance in the NAMS region.

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