scholarly journals The North American Monsoon GPS Transect Experiment 2013

2016 ◽  
Vol 97 (11) ◽  
pp. 2103-2115 ◽  
Author(s):  
Yolande L. Serra ◽  
David K. Adams ◽  
Carlos Minjarez-Sosa ◽  
James M. Moker ◽  
Avelino F. Arellano ◽  
...  
Keyword(s):  
Water Vapor ◽  
North American ◽  
Water Cycle ◽  
Precipitable Water ◽  
Annual Rainfall ◽  
North American Monsoon ◽  
Atmospheric Sciences ◽  
The North ◽  
Northwestern Mexico ◽  
The Impact

Abstract Northwestern Mexico experiences large variations in water vapor on seasonal time scales in association with the North American monsoon, as well as during the monsoon associated with upper-tropospheric troughs, mesoscale convective systems, tropical easterly waves, and tropical cyclones. Together these events provide more than half of the annual rainfall to the region. A sufficient density of meteorological observations is required to properly observe, understand, and forecast the important processes contributing to the development of organized convection over northwestern Mexico. The stability of observations over long time periods is also of interest to monitor seasonal and longer-time-scale variability in the water cycle. For more than a decade, the U.S. Global Positioning System (GPS) has been used to obtain tropospheric precipitable water vapor (PWV) for applications in the atmospheric sciences. There is particular interest in establishing these systems where conventional operational meteorological networks are not possible due to the lack of financial or human resources to support the network. Here, we provide an overview of the North American Monsoon GPS Transect Experiment 2013 in northwestern Mexico for the study of mesoscale processes and the impact of PWV observations on high-resolution model forecasts of organized convective events during the 2013 monsoon. Some highlights are presented, as well as a look forward at GPS networks with surface meteorology (GPS-Met) planned for the region that will be capable of capturing a wider range of water vapor variability in both space and time across Mexico and into the southwestern United States.

The Impact of Assimilating GPS Precipitable Water Vapor in Convective-Permitting WRF-ARW on North American Monsoon Precipitation Forecasts over Northwest Mexico

2021 ◽  
Author(s):  
Christoforus Bayu Risanto ◽  
Christopher L. Castro ◽  
Avelino F. Arellano ◽  
James M. Moker ◽  
David K. Adams
Keyword(s):  
Water Vapor ◽  
Data Assimilation ◽  
North American ◽  
Precipitable Water ◽  
Precipitable Water Vapor ◽  
North American Monsoon ◽  
Convective Systems ◽  
Northwest Mexico ◽  
Dewpoint Temperature ◽  
The Impact

AbstractWe assess the impact of GPS precipitable water vapor (GPS-PWV) data assimilation (DA) on short-range North American monsoon (NAM) precipitation forecasts, across 38 days with weak synoptic forcing, during the NAM GPS Hydrometeorological Network field campaign in 2017 over northwest Mexico. Utilizing an ensemble-based data assimilation technique, the GPS-PWV data retrieved from 18 observation sites are assimilated every hour for 12 hours into a 30-member ensemble convective-permitting (2.5 km) Advanced Research version of the Weather Research and Forecasting (WRF-ARW) model. As the assimilation of the GPS-PWV improves the initial condition of WRF by reducing the root mean square error and bias of PWV across 1200-1800 UTC, this also leads to an improvement in capturing nocturnal convection of mesoscale convective systems (MCSs; after 0300 UTC) and to an increase by 0.1 mm h-1 in subsequent precipitation during the 0300-0600 UTC period relative to no assimilation of the GPS-PWV (NODA) over the area with relatively more observation sites. This response is consistent with observed precipitation from the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement Final Precipitation product. Moreover, compared to the NODA, we find that the GPS-PWV DA decreases cloud top temperature, increases most unstable convective available energy and surface dewpoint temperature, and thus creates a more favorable condition for convective organization in the region.

Impact of Tropical Easterly Waves on the North American Monsoon

2007 ◽  
Vol 20 (7) ◽  
pp. 1219-1238 ◽  
Author(s):  
Jennifer L. Adams ◽  
David J. Stensrud
Keyword(s):  
United States ◽  
Boundary Conditions ◽  
North American ◽  
Moisture Flux ◽  
North American Monsoon ◽  
Southern Plains ◽  
The North ◽  
Gulf Surges ◽  
Northwestern Mexico ◽  
The Impact

Abstract The North American monsoon (NAM) is a prominent summertime feature over northwestern Mexico and the southwestern United States. It is characterized by a distinct shift in midlevel winds from westerly to easterly as well as a sharp, marked increase in rainfall. This maximum in rainfall accounts for 60%–80% of the annual precipitation in northwestern Mexico and nearly 40% of the yearly rainfall over the southwestern United States. Gulf surges, or coastally trapped disturbances that occur over the Gulf of California, are important mechanisms in supplying the necessary moisture for the monsoon and are hypothesized in previous studies to be initiated by the passage of a tropical easterly wave (TEW). Since the actual number of TEWs varies from year to year, it is possible that TEWs are responsible for producing some of the interannual variability in the moisture flux and rainfall seen in the NAM. To explore the impact of TEWs on the NAM, four 1-month periods are chosen for study that represent a reasonable variability in TEW activity. Two continuous month-long simulations are produced for each of the selected months using the Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model. One simulation is a control run that uses the complete boundary condition data, whereas a harmonic analysis is used to remove TEWs with periods of approximately 3.5 to 7.5 days from the model boundary conditions in the second simulation. These simulations with and without TEWs in the boundary conditions are compared to determine the impact of the waves on the NAM. Fields such as meridional moisture flux, rainfall totals, and surge occurrences are examined to define similarities and differences between the model runs. Results suggest that the removal of TEWs not only reduces the strength of gulf surges, but also rearranges rainfall over the monsoon region. Results further suggest that TEWs influence rainfall over the Southern Plains of the United States, with TEWs leading to less rainfall in this region. While these results are only suggestive, since rainfall is the most difficult model forecast parameter, it may be that TEWs alone can explain part of the inverse relationship between NAM and Southern Plains rainfall.

scholarly journals Evaluating Forecast Skills of Moisture from Convective-Permitting WRF-ARW Model during 2017 North American Monsoon Season

Atmosphere ◽  
2019 ◽  
Vol 10 (11) ◽  
pp. 694 ◽  
Author(s):  
Christoforus Bayu Risanto ◽  
Christopher L. Castro ◽  
James M. Moker ◽  
Avelino F. Arellano ◽  
David K. Adams ◽  
...  
Keyword(s):  
North American ◽  
Monsoon Season ◽  
Precipitable Water ◽  
Weather Forecast ◽  
Moisture Flux ◽  
Rain Gauge ◽  
North American Monsoon ◽  
Convective Systems ◽  
The North ◽  
Northwestern Mexico

This paper examines the ability of the Weather Research and Forecasting model forecast to simulate moisture and precipitation during the North American Monsoon GPS Hydrometeorological Network field campaign that took place in 2017. A convective-permitting model configuration performs daily weather forecast simulations for northwestern Mexico and southwestern United States. Model precipitable water vapor (PWV) exhibits wet biases greater than 0.5 mm at the initial forecast hour, and its diurnal cycle is out of phase with time, compared to observations. As a result, the model initiates and terminates precipitation earlier than the satellite and rain gauge measurements, underestimates the westward propagation of the convective systems, and exhibits relatively low forecast skills on the days where strong synoptic-scale forcing features are absent. Sensitivity analysis shows that model PWV in the domain is sensitive to changes in initial PWV at coastal sites, whereas the model precipitation and moisture flux convergence (QCONV) are sensitive to changes in initial PWV at the mountainous sites. Improving the initial physical states, such as PWV, potentially increases the forecast skills.

scholarly journals Convective-Permitting Hindcast Simulations during the North American Monsoon GPS Transect Experiment 2013: Establishing Baseline Model Performance without Data Assimilation

2018 ◽  
Vol 57 (8) ◽  
pp. 1683-1710 ◽  
Author(s):  
James M. Moker ◽  
Christopher L. Castro ◽  
Avelino F. Arellano ◽  
Yolande L. Serra ◽  
David K. Adams
Keyword(s):  
North American ◽  
Initial Conditions ◽  
Model Performance ◽  
Precipitable Water ◽  
Border Region ◽  
Precipitation Forecast ◽  
North American Monsoon ◽  
Forecast System ◽  
The North ◽  
Northwestern Mexico

AbstractDuring the North American monsoon global positioning system (GPS) Transect Experiment 2013, daily convective-permitting WRF simulations are performed in northwestern Mexico and the southern Arizona border region using the operational Global Forecast System (GFS) and North American Mesoscale Forecast System (NAM) models as lateral boundary forcing and initial conditions. Compared to GPS precipitable water vapor (PWV), the WRF simulations display a consistent moist bias in the initial specification of PWV leading to convection beginning 3–6 h early. Given appreciable observed rainfall, days are classified as strongly and weakly forced based only on the presence of an inverted trough (IV); gulf surges did not noticeably impact the development of mesoscale convective systems (MCSs) and related convection in northwestern Mexico. Strongly forced days display higher modeled precipitation forecast skill than weakly forced days in the slopes of the northern Sierra Madre Occidental (SMO) away from the crest, especially toward the west where MCSs account for the greatest proportion of all monsoon-related precipitation. A case study spanning 8–10 July 2013 illustrates two consecutive days when nearly identical MCSs evolved over northern Sonora. Although a salient MCS is simulated on the strongly forced day (9–10 July 2013) when an IV is approaching the core monsoon region, a simulated MCS is basically nonexistent on the weakly forced day (8–9 July 2013) when the IV is farther away. The greater sensitivity to the initial specification of PWV in the weakly forced day suggests that assimilation of GPS-derived PWV for these types of days may be of greatest value in improving model precipitation forecasts.

Observational Analysis of an Upper-Level Inverted Trough during the 2004 North American Monsoon Experiment

2010 ◽  
Vol 138 (9) ◽  
pp. 3540-3555 ◽  
Author(s):  
Zachary O. Finch ◽  
Richard H. Johnson
Keyword(s):  
North American ◽  
Cyclonic Circulation ◽  
Primary Data ◽  
North American Monsoon ◽  
The West ◽  
Colorado State University ◽  
Downward Motion ◽  
The North ◽  
Northwestern Mexico ◽  
Upper Level

Abstract Upper-level inverted troughs (IVs) associated with midlatitude breaking Rossby waves or tropical upper-troposphere troughs (TUTTs) have been identified as important contributors to the variability of rainfall in the North American monsoon (NAM) region. However, little attention has been given to the dynamics of these systems owing to the sparse observational network over the NAM region. High temporal and spatial observations taken during the 2004 North American Monsoon Experiment (NAME) are utilized to analyze a significant IV that passed over northwestern Mexico from 10 to 13 July 2004. The Colorado State University gridded dataset, which is independent of model analysis over land, is the primary data source used in this study. Results show that the 10–13 July IV disturbance was characterized by a warm anomaly around 100 hPa and a cold anomaly that extended from 200 to 700 hPa. The strongest cyclonic circulation was in the upper levels around 200 hPa. Quasigeostrophic (QG) diagnostics indicate that the upper-level low forced weak subsidence (weak rising motion) to the west (east) of its center. Net downward motion to the west was a result of the Laplacian of thermal advection (forcing subsidence) outweighing differential vorticity advection (forcing weak upward motion). Despite the QG forcing of downward motion west of the upper-level IV, enhanced convection occurred west of the IV center along the western slopes of the Sierra Madre Occidental (SMO). This seemingly contradictory behavior can be explained by noting that the upper-level IV induced a midlevel cyclonic circulation, with northeasterly (southeasterly) midlevel flow to the west (east) of its center. Increased mesoscale organization of convection along the SMO foothills was found to be collocated with IV-enhanced northeasterly midlevel flow and anomalous northeasterly shear on the western (leading) flank of the system. It is proposed that the upper-level IV increased the SMO-perpendicular midlevel flow as well as the wind shear, thereby creating an environment favorable for convective storms to grow upscale as they moved off the high terrain.

scholarly journals Vegetation Dynamics within the North American Monsoon Region

2011 ◽  
Vol 24 (6) ◽  
pp. 1763-1783 ◽  
Author(s):  
Giovanni Forzieri ◽  
Fabio Castelli ◽  
Enrique R. Vivoni
Keyword(s):  
North American ◽  
Vegetation Dynamics ◽  
Vegetation Index ◽  
North American Monsoon ◽  
Terrain Attributes ◽  
The North ◽  
Short Period ◽  
Long Term Trends ◽  
Northwestern Mexico

Abstract The North American monsoon (NAM) leads to a large increase in summer rainfall and a seasonal change in vegetation in the southwestern United States and northwestern Mexico. Understanding the interactions between NAM rainfall and vegetation dynamics is essential for improved climate and hydrologic prediction. In this work, the authors analyze long-term vegetation dynamics over the North American Monsoon Experiment (NAME) tier I domain (20°–35°N, 105°–115°W) using normalized difference vegetation index (NDVI) semimonthly composites at 8-km resolution from 1982 to 2006. The authors derive ecoregions with similar vegetation dynamics using principal component analysis and cluster identification. Based on ecoregion and pixel-scale analyses, this study quantifies the seasonal and interannual vegetation variations, their dependence on geographic position and terrain attributes, and the presence of long-term trends through a set of phenological vegetation metrics. Results reveal that seasonal biomass productivity, as captured by the time-integrated NDVI (TINDVI), is an excellent means to synthesize vegetation dynamics. High TINDVI occurs for ecosystems with a short period of intense greening tuned to the NAM or with a prolonged period of moderate greenness continuing after the NAM. These cases represent different plant strategies (deciduous versus evergreen) that can be adjusted along spatial gradients to cope with seasonal water availability. Long-term trends in TINDVI may also indicate changing conditions favoring ecosystems that intensively use NAM rainfall for rapid productivity, as opposed to delayed and moderate greening. A persistence of these trends could potentially result in the spatial reorganization of ecosystems in the NAM region.

scholarly journals Comments on “Regional Impacts of Irrigation in Mexico and the Southwestern United States on Hydrometeorological Fields in the North American Monsoon Region”

2018 ◽  
Vol 19 (2) ◽  
pp. 477-481 ◽  
Author(s):  
Theodore J. Bohn ◽  
Enrique R. Vivoni
Keyword(s):  
North American ◽  
Gulf Of California ◽  
Wrf Model ◽  
Summer Precipitation ◽  
Atmospheric Modeling ◽  
Irrigated Agriculture ◽  
North American Monsoon ◽  
Impact Surface ◽  
The North ◽  
The Impact

Abstract For their investigation of the impact of irrigated agriculture on hydrometeorological fields in the North American monsoon (NAM) region, Mahalov et al. used the Weather Research and Forecasting (WRF) Model to simulate weather over the NAM region in the summer periods of 2000 and 2012, with and without irrigation applied to the regional croplands. Unfortunately, while the authors found that irrigated agriculture may indeed influence summer precipitation, the magnitude, location, and seasonality of their irrigation inputs were substantially inaccurate because of 1) the assumption that pixels classified as “irrigated cropland” are irrigated during the summer and 2) an outdated land cover map that misrepresents known agricultural districts. The combined effects of these errors are 1) an overestimation of irrigated croplands by a factor of 3–10 along the coast of the Gulf of California and by a factor of 1.5 near the Colorado River delta and 2) a large underestimation of irrigation by a factor of 7–10 in Chihuahua, particularly in 2012. Given the sensitivity of the WRF simulations conducted by Mahalov et al. to the presence of irrigated agriculture, it is expected that the identified errors would significantly impact surface moisture and energy fluxes, resulting in noticeably different effects on precipitation. The authors suggest that the analysis of irrigation effects on precipitation using coupled land–atmospheric modeling systems requires careful specification of the spatiotemporal distribution of irrigated croplands.

scholarly journals Evaluation of PERSIANN-CCS Rainfall Measurement Using the NAME Event Rain Gauge Network

2007 ◽  
Vol 8 (3) ◽  
pp. 469-482 ◽  
Author(s):  
Yang Hong ◽  
David Gochis ◽  
Jiang-tao Cheng ◽  
Kuo-lin Hsu ◽  
Soroosh Sorooshian
Keyword(s):  
North American ◽  
Monsoon Season ◽  
Remotely Sensed ◽  
Rain Gauge ◽  
Space Time ◽  
North American Monsoon ◽  
The North ◽  
Precipitation Estimates ◽  
Northwestern Mexico ◽  
Rain Gauge Network

Abstract Robust validation of the space–time structure of remotely sensed precipitation estimates is critical to improving their quality and confident application in water cycle–related research. In this work, the performance of the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks-Cloud Classification System (PERSIANN-CCS) precipitation product is evaluated against warm season precipitation observations from the North American Monsoon Experiment (NAME) Event Rain Gauge Network (NERN) in the complex terrain region of northwestern Mexico. Analyses of hourly and daily precipitation estimates show that the PERSIANN-CCS captures well active and break periods in the early and mature phases of the monsoon season. While the PERSIANN-CCS generally captures the spatial distribution and timing of diurnal convective rainfall, elevation-dependent biases exist, which are characterized by an underestimate in the occurrence of light precipitation at high elevations and an overestimate in the occurrence of precipitation at low elevations. The elevation-dependent biases contribute to a 1–2-h phase shift of the diurnal cycle of precipitation at various elevation bands. For reasons yet to be determined, the PERSIANN-CCS significantly underestimated a few active periods of precipitation during the late or “senescent” phase of the monsoon. Despite these shortcomings, the continuous domain and relatively high spatial resolution of PERSIANN-CCS quantitative precipitation estimates (QPEs) provide useful characterization of precipitation space–time structures in the North American monsoon region of northwestern Mexico, which should prove useful for hydrological applications.

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