A31A-01
Diurnal Cycle of Surface Flows During NAME and Comparison to Model Reanalysis
During the North American Monsoon Experiment (NAME) an unprecedented surface data set of winds and thermodynamic variables was collected over the core monsoon region. The surface network included 63 automated sites with 1-30 min resolution data, 27 SMN operational sites (1-3 hourly data), and 56 US operational sites (1-3 hourly data) along the northern fringe of the monsoon region. These data, along with twice daily QuikSCAT oceanic surface winds, were quality controlled and objectively analyzed on to a uniform grid with quarter-degree, 1-h resolution for the period from 1 July - 15 August. An important application of the gridded winds is their use in diagnosing surface vertical motion due to slope flows over the Sierra Madre Occidental (SMO) terrain. With this dataset we examine the diurnal characteristics of surface fields as the monsoon evolves and compare these analyses to similar surface products from the special North American Regional Reanalysis (NARR) for NAME. Observed surface fields indicate that a robust land-sea breeze circulation is present over most of Gulf of California (GOC) region in response to the strong diurnal heating of land masses on both sides of the gulf. For reasons unclear at this time, many features of this land-sea breeze circulation are missing in the NARR. Evolution of the diurnal cycle of temperature and the land- sea breeze circulation as the monsoon progresses through the season shows a strong sensitivity to rainfall over the SMO and the coastal plains. Such a relationship likely reflects changes in land surface characteristics, such as evapotranspiration and albedo, as the forests of the SMO respond to monsoonal rains.
A31A-02
Role of Mesoscale Convective Systems During Gulf of California Moisture Surges
This paper studies the influence of organized convective activity in modulating moisture surges that develop during the North American Monsoon System along the Gulf of California using a multiyear set of surge events. As seen in different observational case studies during the North American Monsoon Experiment, multiple effects can be present simultaneously, which constitutes a challenge in identifying surges based on their forcings because they may have occurred as a superposition of forcing effects. A surge classification technique will be developed to discriminate surge events based on the convective activity taking place during the surge lifetime in different sector along the Gulf of California. The occurrence of organized convection in the form of Mesoscale Convective Systems (MCS's) can be identified by using cloud top temperature thresholds from International Satellite Cloud Climatology Project (ISCCP) products (this data consist of a 23 years of GOES imagery with 10km horizontal resolution at 3-hourly intervals available from 1983). Using direct inspection of the observations and other systematic approaches (such as discriminant analysis) permits stratifing the surges that are synoptically forced by either TEW's, TCs, or MCS events; the later presumably triggers or impacts surges more locally. Mean surge environments are composed by surge type using the NCEP North American Regional Reanalysis (NARR) products available from 1979 to the present at 3-hourly periods with horizontal resolution of 32 Km. Validation of the NARR are performed using NAME data sets (e.g. using aircraft data) in order to examine its utility as a diagnostic tool in the composites. The time resolution used to identify and diagnose surges, permits an exploration of the surge lifetime and diurnal variability. The large-scale dynamics acting of the surge will be revised and quantified for the different types of forcing. The results highlight the relative impact on the wind field produced by MCSs in the surge evolution.
A31A-03
An Observational and Modeling Study of an Atmospheric Internal Bore During NAME 2004
Atmospheric internal bores have been identified and studied in a variety of locations around the world. However, until now, atmospheric bores have not been explicitly reported in the North American monsoon region. Observations from the North American Monsoon Experiment (NAME) 2004, including soundings, surface observations, and wind profilers have been used to identify and describe the structure, dynamics and significance of an atmospheric internal undular bore in the NAME region along the Gulf of California (GoC). Such bores could potentially be important in GoC monsoon surges, which are often instrumental in bringing abundant moisture to the southwestern United States. An undular bore was identified at Bahia Kino in northwestern Mexico during the late evening of 31 July 2004, and was hypothesized to have developed from the interaction of an outflow from a large mesoscale convective system (MCS), which developed along the western slopes of the Sierra Madre Occidental during the afternoon, and a surface stable layer. The vertical structure and undular nature of the bore was initially identified from 915-MHz wind profiler data. Results show a series of waves along the bore's leading edge and turbulent mixing of air from above the stable layer to the surface on the downstream face of the leading undulation. The speed of the bore calculated from satellite imagery and surface observations (16.5 ms-1) compared favorably with the speed of a bore from hydraulic theory. In order to further investigate the formation and dissipation mechanisms of the bore, a real-data simulation of the event was performed using version 2.1.2 of the advanced research Weather and Forecasting model (WRF). Results show the model captured the structure of the bore but it was produced too far south compared to observations as the MCS also developed too far south. Results indicate the bore formed due to the collision between the MCS outflow and a stable layer formed by a sea breeze from the GoC and was maintained by wave trapping from an elevated stable layer. It is suggested that the bore dissipated due to enhanced turbulence as the surface stable layer on which it propagated reduced in depth. Explanations of the model results will be presented.
A31A-04
Assessment of the NCEP CFS GCM on the Predictability of the North American Monsoon
Predictablility of the North American monsoon circulation is investigated with the 1981-2004 hindcast suite of the NCEP CFS coupled GCM and experimental forecast runs of 60-day length for select years. The forecast runs were made in the horizontal resolution of T62, T126 and T254 to investigate the impact of the spatial resolution on the depiction of monsoon circulation. The hindcasts were made in T62 resolution. Emphasis is on the prediction of precipitation and accompanying atmospheric circulation. Also investigated is the onset phase of the monsoon over the NAME Core and Arizona /New Mexico regions. Some of these features will also be studied in high resolution simulations with the T382 CFS.
A31A-05
Moisture parameters from models and analyses for NAME
We analyzed surface total column parameters, including evaporation, precipitation, precipitable water and water vapor fluxes and divergence, during the warm season (May-October) of two focus years (1990 and 2004) over the North American Monsoon Experiment region, i.e., SW United States and NW Mexico. We compared the calculated values of these parameters, as well as the total moisture budget, from the regional models that participated in the NAME Model Assessment Project campaign and from the North American Regional Reanalysis. We noted considerable differences in precipitation, water vapor divergence, and direction of moisture transport vectors over the North American Monsoon region in the two focus years. The NARR results also identified the characteristics of the moisture seasonal variability, and some high frequency signals within it, including the role of the Sea of Cortez/Gulf of California in the moisture budget. Going beyond the focus years, the NARR output was used to determine the different properties of the water vapor parameters in very wet and very dry years.
A31A-06
Impact of Variable SST on Simulated Warm Season Precipitation
The Colorado State University - Regional Atmospheric Modeling System (CSU-RAMS) is being used to examine the variability in monsoon-related warm season precipitation over Mexico and the United States due to variability in SST. Given recent improvements and increased resolution in satellite derived SSTs it is pertinent to examine the sensitivity of the RAMS model to the variety of SST data sources that are available. In particular, we are examining this dependence across continental scales over the full warm season, as well as across the regional scale centered around the Gulf of California on time scales of individual surge events. In this study we performed an ensemble of simulations that include the 2002, 2003, and 2004 warm seasons with use of the Climatology, Reynold's, AVHRR, and MODIS SSTs. From the seasonal 90-day simulations with 30km grid spacing, it was found that variations in surface latent heat flux are directly linked to differences in SST. Regions with cooler (warmer) SST have decreased (increased) moisture flux from the ocean which is in proportion to the magnitude of the SST difference. Over the eastern Pacific, differences in low-level horizontal moisture flux show a general trend toward reduced fluxes over cooler waters and very little inland impact. Over the Gulf of Mexico, however, there is substantial variability for each dataset comparison, despite having only limited variability among the SST data. Causes of this unexpected variability are not straight-forward. Precipitation impacts are greatest near the southern coast of Mexico and along the Sierra Madres. Precipitation variability over the CONUS is rather chaotic and is limited to areas impacted by the Gulf of Mexico or monsoon convection. Another unexpected outcome is the lack of variability in areas near the northern Gulf of California where SST and latent heat flux variability is a maximum. From the 7-day surge period simulations at 7km grid spacing, we found that SST differences on the higher resolution nested grid reveal fine scale variability that is otherwise smoothed out or unapparent on the coarser grid. Unlike the coarse grid, the latent heat flux, temperature, and moisture transport differences on the fine grid reveal an inland impact. This is likely due to fine scale variability in onshore moisture transport and sea- breeze circulations which may alter monsoonal convection and precipitation. However, only the largest SST differences (spatially and in magnitude) tend to invoke large, coherent responses in moisture flux. The SST variability at high resolution produces relatively large differences in precipitation that are focused along the slopes of the SMO, with a tendency toward greater variability along the western slope adjacent to the coast. The precipitation differences are of fine resolution, with variability of +/- 30 mm (over 5 days) along the length of the SMO. Variability on the fine grid also invokes precipitation changes over AZ/NM that are not resolved on the coarse grid. Vertical cross-sections examined along the GoC during the surge episode revealed variations in the moisture and temperature structure of the surge. The cooler SSTs in the climatological dataset produced the greatest variability compared to the other datasets. The surge produced from climatology SSTs was nearly 5g/kg drier and up to 4°C cooler compared to surges influenced by the SST datasets. The overall northward propagation of the surge appeared unaffected by the SSTs.
A31A-07
Climatology of Mexico: a Description Based on Clustering Analysis
Climate regions of Mexico are delimitated using hierarchical clustering analysis (HCA). We assign the variables, precipitation and temperature, to groups or clusters based on similar statistical characteristics. Since meteorological stations in Mexico expose a heterogonous geographic distribution, we used principal components analysis (PCA) to obtain a standardized reduced matrix to apply conveniently HCA. We consider monthly means of maxima and minima temperature and monthly accumulated precipitation from a meteorological dataset of the National Water Commission of Mexico. It allows defining groups of station delimiting regions of similar climate. It also allows describing the regional effect of events such as the Mexican monsoon and ENSO.
A31A-08
Warm Water Pools of the Western Caribbean and Eastern Tropical Pacific: Their Influence on Intraseasonal Rainfall Regimes and Tropical Storm Activity in Mexico
A dipole in tropical cyclone development between the Caribbean and the eastern tropical Pacific will be examined relative to its affect on southern Mexican rainfall. With the change over in the AMO and PDO in 1994 and 1998, respectively, tropical storm genesis has been increasing in the Caribbean while declining in the tropical east Pacific. This dipole in tropical cyclone development appears to be related to changes in the pre storm season heat content of the two ocean basins (data Scripps Institution of Oceanography). Preliminary work indicates that if the Caribbean is warmer than the Pacific by late May the dipole will be accentuated with a pronounced decrease in tropical storms in the east Pacific with an early and prolonged season in the Caribbean. In recent years there appears to have been an increase in the intensity and duration of midsummer drought (Canicula) in Mexico associated with changes in the PDO and AMO. These long term ocean oscillations appear to control the dipole in the strength of the Caribbean and East Pacific warm pools. Mid summer drought is a normal occurrence in much of Mexico and Central America, but the intensified droughts of the recent period have stressed the agricultural community of the region. Based on preliminary work, it appears that the recent increased frequency of midsummer drought can be linked to a shift in the warmest pool from the East Pacific to the Caribbean.
A31A-09
Applications of monsoon research: Opportunities to inform decisionmaking and reduce regional vulnerability
This presentation will describe ongoing efforts to understand interactions between the North American Monsoon and society, in order to develop applications for monsoon research in a highly complex, multicultural and binational region. The North American Monsoon is an annual precipitation regime that begins in early June in Mexico and progresses northward to the southwestern United States. The region includes stakeholders in large urban complexes, productive agricultural areas, and sparsely populated arid and semi-arid ecosystems. The political, cultural, and socioeconomic divisions between the U.S. and Mexico create a broad range of sensitivities to climate variability as well as capacities to use forecasts and other information to cope with climate. We will highlight methodologies to link climate science with society and analyze opportunities for monsoon science to benefit society in four sectors: natural hazards management, agriculture, public health, and water management. We present a synthesized list of stakeholder needs and a calendar of decisions to help scientists link user needs to potential forecasts and products. To ensure usability of forecasts and other research products, we recommend iterative scientist-stakeholder interactions, through integrated assessments. These knowledge- exchange interactions can improve the capacity for stakeholders to use forecasts thoughtfully and inform the development of research, and for the research community to obtain feedback on climate-related products and receive insights to guide research direction. We expect that integrated assessments can capitalize on the opportunities for monsoon science to inform decisionmaking, in the best instances, reduce regional climate vulnerabilities and enhance regional sustainability