Final Report
Project Title: Analysis of Upper Air Climatology to Support Research on Air Quality of
the U.S.-Mexican Borderlands
SCERP Project Number: AQ94-OF-8
Principal Investigator: Anthony J. Brazel
Arizona State University
Goal: The goal of this research is to further investigate low level atmospheric sounding
data collected by researchers on the University of Texas El Paso (UTEP) campus in the
El Paso area for the purposes of understanding variations of temperature and wind in the
boundary layer zone. This investigation assists in specifying meteorologicalclimatological-related input information for modeling air flow with Diagnostic Wind
Models (DWMs) for our area of interest in Nogales, AZ, where no such low level
atmospheric gradient data are available. Although exact transferability is not possible to
Nogales, the results are expected to provide insights and guidance for running refined
versions of DWMs for that region.
Rationale: Preserving good air quality along the border region of U.S./Mexico requires
the science of knowing sources of pollutants and an accurate understanding of
meteorological and climatological effects on dispersion across the complex terrain of the
border area. Air quality models and resultant policy development will become more
accurate and reliable as a result. Diagnostic wind models and air quality models require
various atmospheric inputs that are critical to the accuracy of dispersion estimates and
particulate level predictions for the region.
Research on this project consisted of reviewing a data base developed from UTEP's
surface Doppler Radar and Radio Acoustic Sounder (DRRAS) equipment for the winter
of 1994 and reported in a previous report to SCERP for the period March 1, 1994 to
December 1, 1994 by Jack Smith of UTEP. All explanations of the equipment and
observations are included in the Smith report. The observations include temperature and
wind measurements on an hourly basis from the surface to over 4000 m in the lower
atmosphere. Upper air sounding data taken from the National Weather Service on a twice
daily basis typically include little detail in the zone below 1500 m. These data are
available from typical NWS first order upper air stations in the region (e.g., El Paso NWS
site), but are of limited value for inputs into air quality models which require knowledge
of low level surface flows in complex terrain and on an hourly observational or modeling
basis. Gradients of the DRRAS-derived wind and temperature data variables are useful
for verifying airshed modeling input assumptions for complex terrain situations and for
parameter estimation for areas such as Nogales, AZ were no such measurements are
available.
Approach: Hourly data were obtained from J. Smith of UTEP to review. These data
were placed in monthly/hourly formats, analyzed for completeness, and selected days
plotted for analysis of the low level wind and temperature profiles above the surface,
especially for suspect days of low flows and synoptically calm periods (periods of
importance in air quality analysis in winter). Standard El Paso first order weather station
surface data of temperature and wind were merged into the database for comparison with
the DRRAS data. Simple case examples of the wind and temperature profiles are
presented in this research. All data are submitted in diskette form for researchers, and
were graciously and originally provided by Jack Smith of UTEP.
Status: Many missing cases exist in the data base, for reasons of instrumental errors and
problems occurring in sampling with DRRAS equipment, so that only selected examples
of the utility of the data can be presented. Results indicate, for low flow cases (e.g., wind
speeds well less than 6 m/s) and for diurnally varying wind in line with local topography
in the El Paso region (e.g., ca. SE/NW), that boundary layer wind profiles consistently
different below ca. 800 m (roughly terrain obstacle height in the region) than above that
level in the free air. An inspection of temperature profiles indicate strong inversions,
particularly in AM periods below the 200-400 m above ground level (see examples in
Appendix I and II). Inversions are very shallow and show strong gradients below 200 m
(+3 degC to + 8 degC/100m) in the morning hours. These results are similar to many
measurements of inversions elsewhere in the desert Southwest (e.g., in the Brush Creek
Valley of western Colorado taken with tethered balloon, doppler acoustic sounders, and
other equipment employed by researchers on ASCOT -- Atmospheric Studies in Complex
Terrain).
Gradient data of wind and temperature can be merged with synoptic typing schemes for
the border region, and these data shed light on assumptions used in DWMs and
subsequent air quality modeling with topographic airshed models and complex terrain
models. For example, for DWMs, there are requirements to specify domain-scale stability
information and surface and upper-air wind data. The specific 10 sample days of DRRAS
data used in this study were linked to the synoptic weather catalog for El Paso developed
during a previous SCERP project by the authors (Brazel, 1994). The days (selected days
in November and December, 1994) consisted generally of high pressure prevalence in the
region; which occurs, with the observed temperature and wind characteristics of those
sample days in winter, about 15% of the time. The sample days represent the most
frequent synoptic type occurring in the El Paso region in winter, especially early winter.
Currently, synoptic analyses performed by our group at ASU have been linked to specific
runs of DWMs for the Nogales region (Berman, et al, 1995), and will require further
verification of hourly estimates of temperature and wind gradient assumptions within and
above the boundary layer in order to accurately specify new wind fields and particulate
estimates for the border region.
Estimates of mixing heights from the selected winter calm periods for the El Paso region
from DRRAS data (e.g., 400 m in morning in winter) generally in conformance with
those derived from twice daily upper air soundings of the National Weather Service
reported for winter morning periods. The DRRAS data, however, allow for hourly inputs
for wind and temperature gradients, unlike the NWS data or assumption schemes from
these data. Thus, a constant diurnal potrayal of the mixing properties of the lower
atmosphere can be rendered and eventually merged with DWM runs. Interpolated
temperature gradients from the DRRAS profile data from within a few hundred meters of
the surface down to the surface generally produced surface temperature estimates within
a degree Celsius of the observed surface observation (shelter height ca. 2 m) at the NWS
first order station for early morning and mid-afternoon periods. This is excellent
agreement, given the accuracy of the NWS data, the profile data, and the NWS horizontal
displacement away from the UTEP DRRAS observation locale. Thus, a combination of
the DRRAS data and NWS surface observations may suffice for most applications in
specifying the extremely low level inversion characteristics of the boundary layer
environment.
Practical Use: Wind modeling/air quality assessment approaches, that might require
synoptic level inputs to models on an hourly basis and assumptions regarding temperature
and wind gradients linked to the boundary layer, could use DRRAS type observations for
border region air quality applications. Researchers should replicate and maintain
coordinated observational systems such as DRRAS in important drainage ways along the
U.S./Mexico border region in the future: (a) to ensure accurate modeling applications
requiring hourly inputs and to translate these findings to better development of air quality
policy, (b) to link to locally available near-by standard long term climate stations (NWS
ASOS, upper air, and others), and (c) to assist in resolving remaining research challenges
in understanding low level micro- meso- meteorology and climatology in relation to the
complex terrain across the U.S./Mexico border region environment.
Other Personnel: We have cooperated with Jack Smith of UTEP on the El Paso region,
and are working with G. Hepner and associates at the University of Utah on Nogales.
Data Sets The original data sets in Microsoft Excel are available from the Principal
Investigator.