Submesoscale Spatiotemporal Variability of North American Monsoon Rainfall over Complex Terrain

2007 ◽  
Vol 20 (9) ◽  
pp. 1751-1773 ◽  
Author(s):  
Mekonnen Gebremichael ◽  
Enrique R. Vivoni ◽  
Christopher J. Watts ◽  
Julio C. Rodríguez
Keyword(s):  
Spatial Pattern ◽  
Diurnal Cycle ◽  
North American ◽  
Rainfall Intensity ◽  
Temporal Dynamics ◽  
Spatiotemporal Variability ◽  
North American Monsoon ◽  
Spatial And Temporal Variability ◽  
Study Region ◽  
Diurnal Cycles

Abstract The authors analyze information from rain gauges, geostationary infrared satellites, and low earth orbiting radar in order to describe and characterize the submesoscale (<75 km) spatial pattern and temporal dynamics of rainfall in a 50 km × 75 km study area located in Sonora, Mexico, in the periphery of the North American monsoon system core region. The temporal domain spans from 1 July to 31 August 2004, corresponding to one monsoon season. Results reveal that rainfall in the study region is characterized by high spatial and temporal variability, strong diurnal cycles in both frequency and intensity with maxima in the evening hours, and multiscaling behavior in both temporal and spatial fields. The scaling parameters of the spatial rainfall fields exhibit dependence on the rainfall rate at the synoptic scale. The rainfall intensity exhibits a slightly stronger diurnal cycle compared to the rainfall frequency, and the maximum lag time between the two diurnal peaks is within 2.4 h, with earlier peaks observed for rainfall intensity. The time of maximum cold cloud occurrence does not vary with the infrared threshold temperature used (215–235 K), while the amplitude of the diurnal cycle varies in such a way that deep convective cells have stronger diurnal cycles. Furthermore, the results indicate that the diurnal cycle of cold cloud occurrence can be used as a surrogate for some basic features of the diurnal cycle of rainfall. The spatial pattern and temporal dynamics of rainfall are modulated by topographic features and large-scale features (circulation and moisture fields as related to geographical location). As compared to valley areas, mountainous areas are characterized by an earlier diurnal peak, an earlier date of maximum precipitation, closely clustered rainy hours, frequent yet small rainfall events, and less dependence of precipitation accumulation on elevation. As compared to the northern section of the study area, the southern section is characterized by strong convective systems that peak late diurnally. The results of this study are important for understanding the physical processes involved, improving the representation of submesoscale variability in models, downscaling rainfall data from coarse meteorological models to smaller hydrological scales, and interpreting and validating remote sensing rainfall estimates.

scholarly journals A Numerical Investigation of Wet and Dry Onset Modes in the North American Monsoon Core Region. Part I: A Regional Mechanism for Interannual Variability

2012 ◽  
Vol 25 (11) ◽  
pp. 3953-3969 ◽  
Author(s):  
Cuauhtémoc Turrent ◽  
Tereza Cavazos
Keyword(s):  
Interannual Variability ◽  
Diurnal Cycle ◽  
North American ◽  
Gulf Of California ◽  
Deep Convection ◽  
Core Region ◽  
Eastern Pacific ◽  
North American Monsoon ◽  
The Core ◽  
The North

In this study the results of two regional fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) simulations forced at their boundaries with low-pass-filtered North American Regional Reanalysis (NARR) composite fields from which synoptic-scale variability was removed are presented. The filtered NARR data are also assimilated into the inner domain through the use of field nudging. The purpose of this research is to investigate wet and dry onset modes in the core region of the North American monsoon (NAM). Key features of the NAM that are present in the NARR fields and assimilated into the regional simulations include the position of the midlevel anticyclone, low-level circulation over the Gulf of California, and moisture flux patterns into the core monsoon region, for which the eastern Pacific is the likely primary source of moisture. The model develops a robust diurnal cycle of deep convection over the peaks of the Sierra Madre Occidental (SMO) that results solely from its radiation scheme and internal dynamics, in spite of the field nudging. The wet onset mode is related to a regional land–sea thermal contrast (LSTC) that is ~2°C higher than in the dry mode, and is further characterized by a northward-displaced midlevel anticyclone, a stronger surface pressure gradient along the Gulf of California, larger mean moisture fluxes into the core region from the eastern Pacific, a stronger diurnal cycle of deep convection, and the more northward distribution of precipitation along the axis of the SMO. A proposed regional LSTC mechanism for NAM onset interannual variability is consistent with the differences between both onset modes.

scholarly journals The Diurnal Cycle of Precipitation over the North American Monsoon Region during the NAME 2004 Field Campaign

2008 ◽  
Vol 21 (4) ◽  
pp. 771-787 ◽  
Author(s):  
Emily J. Becker ◽  
Ernesto Hugo Berbery
Keyword(s):  
Diurnal Cycle ◽  
North American ◽  
Gulf Of California ◽  
Warm Season ◽  
Moisture Flux ◽  
North American Monsoon ◽  
The Core ◽  
The North ◽  
Eta Model ◽  
Diurnal Cycle Of Precipitation

Abstract The structure of the diurnal cycle of warm-season precipitation and its associated fields during the North American monsoon are examined for the core monsoon region and for the southwestern United States, using a diverse set of observations, analyses, and forecasts from the North American Monsoon Experiment field campaign of 2004. Included are rain gauge and satellite estimates of precipitation, Eta Model forecasts, and the North American Regional Reanalysis (NARR). Daily rain rates are of about the same magnitude in all datasets with the exception of the Climate Prediction Center (CPC) Morphing (CMORPH) technique, which exhibits markedly higher precipitation values. The diurnal cycle of precipitation within the core region occurs earlier in the day at higher topographic elevations, evolving with a westward shift of the maximum. This shift appears in the observations, reanalysis, and, while less pronounced, in the model forecasts. Examination of some of the fields associated with this cycle, including convective available potential energy (CAPE), convective inhibition (CIN), and moisture flux convergence (MFC), reveals that the westward shift appears in all of them, but more prominently in the latter. In general, warm-season precipitation in southern Arizona and parts of New Mexico shows a strong effect due to northward moisture surges from the Gulf of California. A reported positive bias in the NARR northward winds over the Gulf of California limits their use with confidence for studies of the moist surges along the Gulf; thus, the analysis is complemented with operational analysis and the Eta Model short-term simulations. The nonsurge diurnal cycle of precipitation lags the CAPE maximum by 6 h and is simultaneous with a minimum of CIN, while the moisture flux remains divergent throughout the day. During surges, CAPE and CIN have modifications only to the amplitude of their cycles, but the moisture flux becomes strongly convergent about 6 h before the precipitation maximum, suggesting a stronger role in the development of precipitation.

scholarly journals Simulation of the North American Monsoon by the NCAR CCM3 and Its Sensitivity to Convection Parameterization

2006 ◽  
Vol 19 (12) ◽  
pp. 2851-2866 ◽  
Author(s):  
J. Craig Collier ◽  
Guang J. Zhang
Keyword(s):  
Relative Humidity ◽  
Diurnal Cycle ◽  
North American ◽  
Large Scale ◽  
The United States ◽  
Experimental Simulation ◽  
Specific Humidity ◽  
North American Monsoon ◽  
Hourly Precipitation ◽  
The North

Abstract Two 9-yr runs of the NCAR Community Climate Model version 3 (CCM3) are compared in their simulations of the North American summer monsoon. In a control simulation, the Zhang–McFarlane deep convection scheme is used. For an experimental simulation, the following modifications to the scheme are implemented. The closure is based on the large-scale forcing of virtual temperature, and a relative humidity threshold on convective parcels lifted from the boundary layer is applied. The sensitivity to these modifications for simulating the North American monsoon is investigated. Model validation relies on hourly precipitation rates from surface gauges over the United States, hourly precipitation rates derived from the combination of microwave and radar measurements from NASA’s Tropical Rainfall Measuring Mission (TRMM) satellite over Mexico, and CAPE values as calculated from temperature, specific humidity, and pressure fields from the NCEP–NCAR reanalysis. Results show that the experimental run improves the timing of the monsoon onset and peak in the regions of core monsoon influence considered here, though it increases a negative bias in the peak monsoon intensity in one region of northern Mexico. Sensitivity of the diurnal cycle of precipitation to modifications in the convective scheme is highly geographically dependent. Using a combination of gauge-based rainfall rates and reanalysis-based CAPE, it is found that improvements in the simulated diurnal cycle are confined to a convective regime in which the diurnal evolution of precipitation is observed to lag that of CAPE. For another regime, in which CAPE is observed to be approximately in phase with precipitation, model phase biases increase nearly everywhere. Some of the increased phase biases in the latter regime are primarily because of application of the relative humidity threshold.

scholarly journals Spatial Variability of the Background Diurnal Cycle of Deep Convection around the GoAmazon2014/5 Field Campaign Sites

2016 ◽  
Vol 55 (7) ◽  
pp. 1579-1598 ◽  
Author(s):  
Casey D. Burleyson ◽  
Zhe Feng ◽  
Samson M. Hagos ◽  
Jerome Fast ◽  
Luiz A. T. Machado ◽  
...  
Keyword(s):  
Spatial Variability ◽  
Satellite Data ◽  
Diurnal Cycle ◽  
Anthropogenic Impacts ◽  
Deep Convection ◽  
Sea Breeze ◽  
Spatial And Temporal Variability ◽  
Trade Winds ◽  
Diurnal Cycles ◽  
Negro River

AbstractThe isolation of the Amazon rain forest makes it challenging to observe precipitation forming there, but it also creates a natural laboratory to study anthropogenic impacts on clouds and precipitation in an otherwise pristine environment. Observations were collected upwind and downwind of Manaus, Brazil, during the “Observations and Modeling of the Green Ocean Amazon 2014–2015” experiment (GoAmazon2014/5). Besides aircraft, most of the observations were point measurements made in a spatially heterogeneous environment, making it hard to distinguish anthropogenic signals from naturally occurring spatial variability. In this study, 15 years of satellite data are used to examine the spatial and temporal variability of deep convection around the GoAmazon2014/5 sites using cold cloud tops (infrared brightness temperatures colder than 240 K) as a proxy for deep convection. During the rainy season, convection associated with the inland propagation of the previous day’s sea-breeze front is in phase with the diurnal cycle of deep convection near Manaus but is out of phase a few hundred kilometers to the east and west. Convergence between the river breezes and the easterly trade winds generates afternoon convection up to 10% more frequently (on average ~4 mm day−1 more intense rainfall) at the GoAmazon2014/5 sites east of the Negro River (T0e, T0t/k, and T1) relative to the T3 site, which was located west of the river. In general, the annual and diurnal cycles of precipitation during 2014 were similar to climatological values that are based on satellite data from 2000 to 2013.

scholarly journals The Relationship of Transient Upper-Level Troughs to Variability of the North American Monsoon System

2009 ◽  
Vol 22 (15) ◽  
pp. 4213-4227 ◽  
Author(s):  
Stephen W. Bieda ◽  
Christopher L. Castro ◽  
Steven L. Mullen ◽  
Andrew C. Comrie ◽  
Erik Pytlak
Keyword(s):  
Diurnal Cycle ◽  
North American ◽  
Low Frequency ◽  
Warm Season ◽  
Early Summer ◽  
North American Monsoon ◽  
The North ◽  
Sst Variability ◽  
Upper Level ◽  
Regional Reanalysis

Abstract Relationships between transient upper-tropospheric troughs and warm season convective activity over the southwest United States and northern Mexico are explored. Analysis of geopotential height and vorticity fields from the North American Regional Reanalysis and cloud-to-ground lightning data indicates that the passage of mobile inverted troughs (IVs) significantly enhances convection when it coincides with the peak diurnal cycle (1800–0900 UTC) over the North American monsoon (NAM) region. The preferred tracks of IVs during early summer are related to the dominant modes of Pacific sea surface temperature (SST) variability. When La Niña–like (El Niño–like) conditions prevail in the tropical Pacific and the eastern North Pacific has a horseshoe-shaped negative (positive) SST anomaly, IVs preferentially track farther north (south) and are slightly (typically one IV) more (less) numerous. These results point to the important role that synoptic-scale disturbances play in modulating the diurnal cycle of precipitation over the NAM region and the significant impact that the statistically supported low-frequency Pacific SST anomalies exert on the occurrence and track of these synoptic transients.

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.

scholarly journals Spatial pattern evaluation of a calibrated national hydrological model – a remote-sensing-based diagnostic approach

2017 ◽  
Vol 21 (12) ◽  
pp. 5987-6005 ◽  
Author(s):  
Gorka Mendiguren ◽  
Julian Koch ◽  
Simon Stisen
Keyword(s):  
Remote Sensing ◽  
Spatial Pattern ◽  
Spatial Patterns ◽  
Hydrological Model ◽  
Temporal Dynamics ◽  
Remote Sensing Data ◽  
Spatiotemporal Variability ◽  
Eof Analysis ◽  
Area Index ◽  
Sensing Data

Abstract. Distributed hydrological models are traditionally evaluated against discharge stations, emphasizing the temporal and neglecting the spatial component of a model. The present study widens the traditional paradigm by highlighting spatial patterns of evapotranspiration (ET), a key variable at the land–atmosphere interface, obtained from two different approaches at the national scale of Denmark. The first approach is based on a national water resources model (DK-model), using the MIKE-SHE model code, and the second approach utilizes a two-source energy balance model (TSEB) driven mainly by satellite remote sensing data. Ideally, the hydrological model simulation and remote-sensing-based approach should present similar spatial patterns and driving mechanisms of ET. However, the spatial comparison showed that the differences are significant and indicate insufficient spatial pattern performance of the hydrological model.The differences in spatial patterns can partly be explained by the fact that the hydrological model is configured to run in six domains that are calibrated independently from each other, as it is often the case for large-scale multi-basin calibrations. Furthermore, the model incorporates predefined temporal dynamics of leaf area index (LAI), root depth (RD) and crop coefficient (Kc) for each land cover type. This zonal approach of model parameterization ignores the spatiotemporal complexity of the natural system. To overcome this limitation, this study features a modified version of the DK-model in which LAI, RD and Kc are empirically derived using remote sensing data and detailed soil property maps in order to generate a higher degree of spatiotemporal variability and spatial consistency between the six domains. The effects of these changes are analyzed by using empirical orthogonal function (EOF) analysis to evaluate spatial patterns. The EOF analysis shows that including remote-sensing-derived LAI, RD and Kc in the distributed hydrological model adds spatial features found in the spatial pattern of remote-sensing-based ET.

scholarly journals Polarimetric Radar Observations of Convection in Northwestern Mexico during the North American Monsoon Experiment

2010 ◽  
Vol 11 (6) ◽  
pp. 1345-1357 ◽  
Author(s):  
Timothy J. Lang ◽  
Steven A. Rutledge ◽  
Robert Cifelli
Keyword(s):  
Liquid Water ◽  
Coastal Plain ◽  
North American ◽  
Water Mass ◽  
North American Monsoon ◽  
Spatial And Temporal Variability ◽  
Polarimetric Radar ◽  
Convective Rainfall ◽  
The North ◽  
Warm Rain

Abstract The spatial and temporal variability of convection during the North American Monsoon Experiment (NAME) was examined via analysis of three-dimensional polarimetric radar data. Terrain bands were defined as the Gulf of California (over water) and elevations of 0–500 m above mean sea level (MSL; coastal plain), 500–1500 m MSL, and >1500 m MSL. Convective rainfall over the Gulf typically featured the smallest values of median volume diameter (D0) regardless of rain rate. Gulf convection also contained reduced precipitation-sized ice water mass but proportionally more liquid water mass compared to convection over land. These maritime characteristics were magnified during disturbed meteorological regimes, which typically featured increased precipitation over the Gulf and adjacent coastal plain. Overall, the results suggest increased reliance on warm-rain collision and coalescence at the expense of ice-based precipitation growth processes for convective rainfall over the Gulf, relative to the land. Over land D0, ice, and liquid water mass all increased with decreasing terrain elevation, suggesting intensification of convection as it moved off the Sierra Madre Occidental. The results are consistent with the hypothesis that both warm-rain and ice-based rainfall processes play important roles in precipitation formation over land. Coastal-plain convection underwent microphysical modifications during disturbed meteorological regimes that were similar to Gulf convection, but the changes were less dramatic. High-terrain convection experienced little microphysical variability regardless of meteorological regime.

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