Observed shifts in land surface conditions during the North American Monsoon: Implications for a vegetation–rainfall feedback mechanism

2010 ◽  
Vol 74 (5) ◽  
pp. 549-555 ◽  
Author(s):  
Luis A. Méndez-Barroso ◽  
Enrique R. Vivoni
Keyword(s):  
North American ◽  
Land Surface ◽  
Feedback Mechanism ◽  
North American Monsoon ◽  
Surface Conditions ◽  
The North

scholarly journals Variation of Hydrometeorological Conditions along a Topographic Transect in Northwestern Mexico during the North American Monsoon

2007 ◽  
Vol 20 (9) ◽  
pp. 1792-1809 ◽  
Author(s):  
Enrique R. Vivoni ◽  
Hugo A. Gutiérrez-Jurado ◽  
Carlos A. Aragón ◽  
Luis A. Méndez-Barroso ◽  
Alex J. Rinehart ◽  
...  
Keyword(s):  
Field Experiment ◽  
North American ◽  
Land Surface ◽  
Spatiotemporal Variability ◽  
North American Monsoon ◽  
Surface Conditions ◽  
The North ◽  
Northwestern Mexico ◽  
Hydrometeorological Conditions ◽  
Atmospheric Variables

Abstract Relatively little is currently known about the spatiotemporal variability of land surface conditions during the North American monsoon, in particular for regions of complex topography. As a result, the role played by land–atmosphere interactions in generating convective rainfall over steep terrain and sustaining monsoon conditions is still poorly understood. In this study, the variation of hydrometeorological conditions along a large-scale topographic transect in northwestern Mexico is described. The transect field experiment consisted of daily sampling at 30 sites selected to represent variations in elevation and ecosystem distribution. Simultaneous soil and atmospheric variables were measured during a 2-week period in early August 2004. Transect observations were supplemented by a network of continuous sampling sites used to analyze the regional hydrometeorological conditions prior to and during the field experiment. Results reveal the strong control exerted by topography on the spatial and temporal variability in soil moisture, with distinct landscape regions experiencing different hydrologic regimes. Reduced variations at the plot and transect scale during a drydown period indicate that homogenization of hydrologic conditions occurred over the landscape. Furthermore, atmospheric variables are clearly linked to surface conditions, indicating that heating and moistening of the boundary layer closely follow spatial and temporal changes in hydrologic properties. Land–atmosphere interactions at the basin scale (∼100 km2), obtained via a technique accounting for topographic variability, further reveal the role played by the land surface in sustaining high atmospheric moisture conditions, with implications toward rainfall generation during the North American monsoon.

Changes in Vegetation Condition and Surface Fluxes during NAME 2004

2007 ◽  
Vol 20 (9) ◽  
pp. 1810-1820 ◽  
Author(s):  
Christopher J. Watts ◽  
Russell L. Scott ◽  
Jaime Garatuza-Payan ◽  
Julio C. Rodriguez ◽  
John H. Prueger ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Land Surface Temperature ◽  
North American ◽  
Land Surface ◽  
Vegetation Index ◽  
Surface Fluxes ◽  
North American Monsoon ◽  
Forest Site ◽  
The North ◽  
Dry Spell

Abstract The vegetation in the core region of the North American monsoon (NAM) system changes dramatically after the onset of the summer rains so that large changes may be expected in the surface fluxes of radiation, heat, and moisture. Most of this region lies in the rugged terrain of western Mexico and very few measurements of these fluxes have been made in the past. Surface energy balance measurements were made at seven sites in Sonora, Mexico, and Arizona during the intensive observation period (IOP) of the North American Monsoon Experiment (NAME) in summer 2004 to better understand how land surface vegetation change alters energy flux partitioning. Satellite data were used to obtain time series for vegetation indices and land surface temperature for these sites. The results were analyzed to contrast conditions before the onset of the monsoon with those afterward. As expected, precipitation during the 2004 monsoon was highly variable from site to site, but it fell in greater quantities at the more southern sites. Likewise, large changes in the vegetation index were observed, especially for the subtropical sites in Sonora. However, the changes in the broadband albedo were very small, which was rather surprising. The surface net radiation was consistent with the previous observations, being largest for surfaces that are transpiring and cool, and smallest for surfaces that are dry and hot. The largest evaporation rates were observed for the subtropical forest and riparian vegetation sites. The evaporative fraction for the forest site was highly correlated with its vegetation index, except during the dry spell in August. This period was clearly detected in the land surface temperature data, which rose steadily in this period to a maximum at its end.

Land Surface Heating and the North American Monsoon Anticyclone: Model Evaluation from Diurnal to Seasonal

2010 ◽  
Vol 23 (15) ◽  
pp. 4096-4106 ◽  
Author(s):  
Patrick Kelly ◽  
Brian Mapes
Keyword(s):  
North American ◽  
Land Surface ◽  
Regional Scale ◽  
Surface Flux ◽  
Turbulent Energy ◽  
Analysis Data ◽  
Surface Heating ◽  
North American Monsoon ◽  
The North ◽  
Seasonal Time Scale

Abstract Data from several regional and global models (including model-based analysis data) are compared with field data from the North American Monsoon Experiment (NAME), from observational sites as well as satellite retrievals. On the regional scale (NAME tier 1.5), sensible heating is shown to exceed latent and is furthermore concentrated in the lower half of the troposphere, so in considering the North American monsoon (NAM) midlevel anticyclone, the authors focus on radiative and turbulent energy fluxes at the surface. Models exhibit large discrepancies in their simulation of the mean diurnal cycle of these fluxes as well as in their sensitivity of evaporative fraction to recent rainfall. Most of the models examined have too much net radiation due to excessive shortwave surface flux (too little cloud) and too much sensible heating. These high biases in sensible heating appear to drive overpredictions of both the daily and seasonal rise of 500-hPa heights in the NAM anticyclone. This diurnal–seasonal resemblance suggests that calibrating surface heating processes using readily field-observed diurnal variations could lead to improvements in seasonal-time-scale NAM simulations.

scholarly journals Predictability of Evapotranspiration Patterns Using Remotely Sensed Vegetation Dynamics during the North American Monsoon

2012 ◽  
Vol 13 (1) ◽  
pp. 103-121 ◽  
Author(s):  
Qiuhong Tang ◽  
Enrique R. Vivoni ◽  
Francisco Muñoz-Arriola ◽  
Dennis P. Lettenmaier
Keyword(s):  
North American ◽  
Land Surface ◽  
Vegetation Dynamics ◽  
Monsoon Season ◽  
Regional Scale ◽  
North American Monsoon ◽  
Onset Date ◽  
Infiltration Capacity ◽  
Area Index ◽  
The North

Abstract The links between vegetation, evapotranspiration (ET), and soil moisture (SM) are prominent in western Mexico—a region characterized by an abrupt increase in rainfall and ecosystem greenup during the North American monsoon (NAM). Most regional-scale land surface models use climatological vegetation and are therefore unable to capture fully the spatiotemporal changes in these linkages. Interannually varying and climatological leaf area index (LAI) were prescribed, both inferred from the space-borne Moderate Resolution Imaging Spectroradiometer (MODIS), as the source of vegetation parameter inputs to the Variable Infiltration Capacity (VIC) model applied over the NAM region for 2001–08. Results at two eddy covariance tower sites for three summer periods were compared and evaluated. Results show that both vegetation greening onset and dormancy dates vary substantially from year to year with a range of more than half a month. The model using climatological LAI tends to predict lower (higher) ET than the model using observed LAI when vegetation greening occurs earlier (later) than the mean greening date. These discrepancies were especially large during approximately two weeks at the beginning of the monsoon. The effect of LAI on ET estimates was about 10% in the Sierra Madre Occidental and 30% in the continental interior. VIC-estimated ET based on interannually varying LAI had high interannual variability at the greening onset and dormancy periods corresponding to the vegetation dynamics. The greening onset date was highly related to ET early in the monsoon season, indicating the potential usefulness of LAI anomalies for predicting early season ET.

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

2013 ◽  
Vol 118 (2) ◽  
pp. 293-305 ◽  
Author(s):  
X. Feng ◽  
M. Bosilovich ◽  
P. Houser ◽  
J.-D. Chern
Keyword(s):  
North American ◽  
Land Surface ◽  
North American Monsoon ◽  
Surface Conditions

Land surface ecohydrology of the North American monsoon system

2010 ◽  
Vol 74 (5) ◽  
pp. 529-530 ◽  
Author(s):  
Enrique R. Vivoni ◽  
Christopher J. Watts ◽  
David J. Gochis
Keyword(s):  
North American ◽  
Land Surface ◽  
North American Monsoon ◽  
The North ◽  
Monsoon System

scholarly journals Role of Antecedent Land Surface Conditions on North American Monsoon Rainfall Variability*

2005 ◽  
Vol 18 (16) ◽  
pp. 3104-3121 ◽  
Author(s):  
Chunmei Zhu ◽  
Dennis P. Lettenmaier ◽  
Tereza Cavazos
Keyword(s):  
North American ◽  
Land Surface ◽  
Snow Water Equivalent ◽  
Rainfall Variability ◽  
Winter Precipitation ◽  
Early Summer ◽  
North American Monsoon ◽  
Mountainous Region ◽  
Monsoon Precipitation ◽  
Surface Conditions

Abstract Possible links between North American Monsoon System (NAMS) seasonal [June–July–August–September (JJAS)] precipitation and premonsoon seasonal land surface conditions including precipitation (P), surface air temperature (Ts), soil moisture (Sm), and snow water equivalent (SWE) anomalies are explored during the 1950–2000 period. A statistically significant inverse relationship is found between monsoon precipitation in an area defined as the Monsoon West (Arizona and western New Mexico) and antecedent winter precipitation in the southwestern (SW) United States and the mountainous region in Utah and Colorado (the predictor area). This linkage is strong during 1965–90 and weak otherwise, as has been suggested by previous studies. A land surface feedback hypothesis is proposed to explain this relationship: more winter P leads to more winter and early spring SWE in the predictor area, hence more spring and early summer Sm, and lower spring and early summer Ts, which induces a weaker onset (and less precipitation) of the NAMS and vice versa. All three links in this hypothesis were tested and the existence of a land memory associated with winter precipitation and snow, which can persist until June, was confirmed. However, the results show that this land memory contributes little to the magnitude of NAM precipitation. Winter snow is negatively correlated to late spring Ts in the SW mountainous region, but not in extreme years. In fact, the premonsoon (June) Ts over the U.S. southwest is inversely related to monsoon precipitation, which is the reverse of what is expected based on the hypothesis. The lack of a significant Sm–Ts–P relationship in most of the SW suggests, based on the constructed Sm dataset, that local premonsoon soil wetness conditions play a minor role in the strength of the monsoon. A strong positive relationship between June Ts anomalies and the large-scale midtropospheric circulation before the onset of the monsoon was found, suggesting that the controlling factor for the premonsoon Ts anomalies may not be local (i.e., not from the land surface). The results suggest that further research is needed to elucidate the nature of land–sea–atmosphere interactions as related to the onset of the monsoon.

scholarly journals Mechanical forcing of the North American monsoon by orography

2021 ◽  
Author(s):  
William Boos ◽  
Salvatore Pascale
Keyword(s):  
North American ◽  
Land Surface ◽  
Global Climate ◽  
Global Climate Model ◽  
Stationary Wave ◽  
Heat Fluxes ◽  
North American Monsoon ◽  
The Core ◽  
The North ◽  
Orographic Rainfall

Abstract The core of the North American monsoon consists of a band of intense rainfall along the west coast of Mexico[1, 2] and is commonly thought to be caused by thermal forcing from both land and the elevated terrain of that region[3-5]. Here we use observations, a global climate model, and stationary wave solutions to show that this rainfall maximum is instead generated when Mexico's Sierra Madre mountains mechanically force an adiabatic stationary wave by diverting extratropical eastward winds toward the equator; eastward, upslope flow in that wave lifts warm and moist air to produce convective rainfall. Land surface heat fluxes do precondition the atmosphere for convection, particularly in summer afternoons, but even if amplified are insufficient for producing the observed rainfall maximum. These results, together with dynamical structures in observations and models, indicate that the core monsoon should be understood as convectively enhanced orographic rainfall in a mechanically forced stationary wave, not as a classic, thermally forced tropical monsoon. This has implications for the response of the North American monsoon to past and future global climate change, making trends in jet stream interactions with orography of central importance.

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