The METCRAX research program


Table of Contents

Introduction

The Meteor Crater Experiment (METCRAX) was a 3-year meteorological research program supported by the Mesoscale Dynamics Division of the U. S. National Science Foundation (NSF) in 2006-2009. A major field experiment was conducted in October 2006 and a second, closely related research program was conducted in the years 2009-2011 to gain additional scientific value from the field experiments. METCRAX investigated the structure and evolution of temperature inversions or cold-air pools that form on a daily basis in topographic basins and valleys. The October 2006 field program was conducted in Arizona's Meteor Crater, a simple near-ideal topographic basin formed by the impact of a meteor. In this basin, the physical processes leading to the buildup and breakdown of temperature inversions and the formation of atmospheric seiches (atmospheric oscillations in the basin caused by wind disturbances at the basin crest) can be studied without the complications introduced by more complex topography.

Who was involved in METCRAX?

Four Principal Investigators (PIs) collaborated in the original METCRAX research program:

Two of these investigators (Whiteman and Zhong) have continued their analyses in the follow-on research program entitled 'Collaborative Research: The diurnal evolution of stable boundary layers in an enclosed basin'.

The one-month-long field study in the Meteor Crater was supported by scientists and technicians from the U. S. National Center for Atmospheric Research (NCAR). The following NCAR personnel led the NCAR instrumentation effort with the meteorological measurement systems stated (to be described more fully below):

Access to the Meteor Crater for the October 2006 field experiment was granted by the Barringer Crater Company, the family corporation that owns the property, and Meteor Crater Enterprises, the property management company that manages the visitor center/museum. The Barringer Crater Company has a long history of supporting science and educational activities at the Meteor Crater. The following Meteor Crater personnel have been very supportive of our research activities and helped us to plan and coordinate our activities and to enhance the educational value of our activities to their visitors.

visitors center

Meteor Crater visitors center/museum. © C. D. Whiteman

METCRAX team

The METCRAX and Meteor Crater team on a visit to the Meteor Crater in November 2005. L to R: Brad Andes, Drew Barringer, Andreas Muschinski, Sharon Zhong, Dave Whiteman and David Kring. © Craig Clements.

What were the scientific objectives of METCRAX?

These two goals were met through meteorological measurements, analysis and modeling.

What was the motivation for this research?

What are the main physical processes in cold-air pool evolution?

The Meteor Crater

The Barringer Meteor Crater is in northern Arizona, and is located off Interstate 40 at exit 233 about 35 miles east of Flagstaff. The crater was formed approximately 50,000 years ago when a meteor of approximately 50-m diameter smashed into the Colorado Plateau at a speed of 12 km/s or 28,600 mph. Further detail on the interesting science of the crater itself and the history of the development of knowledge on the crater are found on the Barringer Crater website and in a publication by Dr. David Kring, a geoscientist/planetary scientist who is a consultant to the Barringer Crater Company.

The crater is 1.2 km (4000 ft) in diameter and 150 m (550 ft) deep. The interior of the crater is generally off-limits to visitors, although there are regular walking tours conducted from the visitor center on a trail that follows the crater's north rim. The crater is accessible only with special permission, and then on a very rough trail that descends into the crater from the northwest. The 'trail' shown descending southward from the visitors center on the following USGS map is not presently usable.

The Meteor Crater is perhaps the best example of an impact crater on earth and, because of the dry climate of the Colorado Plateau, many of the geological features associated with the impact are extremely well preserved here. The high present and future scientific value of the crater requires that the crater be protected against disturbances. One of the goals of METCRAX, therefore, is to minimize disturbances to the crater. Prof. David Kring advises us on sensitive geological areas in the crater.

A terrific set of computer animations of fly-bys of the Meteor Crater has been produced by Marvin Simkin at Arizona State University. The animations are at different resolutions (some have VERY large files) and have been developed in different video formats (avi and Quicktime). Definitely, have a look.

topographic map pf Meteor Crater

USGS topographic map of northern Arizona's Barringer Meteor Crater. The visitors center is on the north rim of the crater. The red squares on the map are 1-mile on a side. Contour interval is 20 ft. Why oh why doesn't the US go metric?

Panorama of Meteor Crater

Panorama of the Meteor Crater looking southward from the visitors center. © C. D. Whiteman

View into Meteor Crater looking south over the visitors center

The visitors center and Meteor Crater, looking south. © Meteor Crater Enterprises, Inc.

Meteor Crater from the north rim

Meteor Crater from the north rim. © C. D. Whiteman

Meteor Crater from north rim trail

Meteor Crater from the north rim trail. © C. D. Whiteman.

The trail that descends into the Meteor Crater from the northwest

The 'trail' that descends into the crater from the northwest rim of Meteor Crater. © C. D. Whiteman.

Dave Whiteman and the astronaut cutout

Dave Whiteman standing next to the 'astronaut' and American flag that have been put at the crater floor so that visitors using the telescope to look into the crater from the visitors center will be able to determine spatial scales in the crater. There is no 'birch john society' on the crater floor; you can run but you can't hide. © C. D. Whiteman.

Johanna Whiteman starting up the trail

Excellent field assistant starting up the trail to the crater rim. © C. D. Whiteman

What were the field experiments like? Instrumenting the Meteor Crater.

Various meteorological measurement equipment was used both outside and inside the crater.

Outside the crater

An Integrated Sounding System (ISS) composed of a radar wind profiler (RWP) and a Radio Acoustic Sounding System (RASS) were operated continuously outside the crater. This combination of remote sensing instruments provided continuous vertical profiles of horizontal winds (from the RWP) and temperatures (from the RASS). Pictures of the instruments and information on their operation are on the NCAR/EOL website. Three-hourly balloon-borne radiosondes were launched from this site during Intensive Operational Periods (IOPs). These radiosondes were tracked using the Global Positioning System to obtain a vertical wind profile during the balloon's ascent. In other words, the radiosondes are actually rawinsondes - i.e., radiosondes that are tracked to get winds.

ISS system

An Integrated Sounding System as deployed elsewhere in winter conditions. The large antenna on the far side of the van is the antenna for the RWP/RASS. The tower collects basic near-surface weather data which supplements the vertical wind and temperature profiles obtained from the RWP and RASS, respectively. NCAR photo.

An Integrated Surface Flux Facility (ISFF) tower was co-located with the RWP/RASS to measure turbulent fluxes of sensible and latent heat, soil heat flux, soil moisture, and solar and terrestrial radiative fluxes on the flat Colorado Plateau outside the crater. Pictures of ISFF towers and further information on their operation and capabilities are provided on the NCAR/EOL website.

ISFF tower

The tower in the foreground is an ISFF tower. Towers such as this are individually configured to serve the particular needs of a given field experiment. Our towers had multiple levels of radiative and energy flux measurements, and also measured winds, soil moisture and soil heat flux. NCAR photo.

Finally, a Doppler sodar was operated continuously near the RWP/RASS site. This instrument used acoustic pulses (i.e., sound) to measure vertical profiles of horizontal wind in the lowest layers of the atmosphere. You can think of the Doppler sodar as an atmospheric 'sonar'.

Doppler sodar in Yosemite National Park

Doppler sodar as deployed in a 2004 experiment in Yosemite National Park. The wooden structure is an acoustic enclosure that is erected around the transmitting/receiving antenna array. The computer and data processing unit are kept in the nearby tent.© Craig Clements.

Inside the crater

A number of instruments were operated continuously inside the crater. Others were operated only during the 7 IOPs that were designated on the basis of weather forecasts during the one-month field period. IOPs were conducted only on 'bluebird' days - days with clear skies and with weak winds above the crater. Some of the heavy instrumentation was flown into the crater by helicopter, as there is no vehicular access into the crater.

The continuously operating instruments included:

Two lines of temperature data loggers (total of 60 loggers). The lines were run approximately east-west and north-south and crossed at the crater center. The lines extended across the crater and down the outside sidewalls of the crater.

Temperature data logger

Temperature data loggers like this one were attached to fence posts. The logger (HOBO®) is the 4" circular disk on the underside of the bracket that is attached to the fencepost and supports the 6-plate solar radiation shield. The temperature sensor, located in the middle of the radiation shield, is shielded from the direct rays of the sun, so that it records the temperature of the air that passes between the plates of the shield.

Maura Hahnenberger holding HOBO

Maura Hahnenberger, a University of Utah student working on the Meteor Crater research, holds a temperature datalogger assembly that is of the type that we used in the Meteor Crater. Approximately 60 of these assemblies were placed on fenceposts that run on north-south and east-west lines across the crater center.

A set of 6 Integrated Surface Flux Facility (ISFF) towers were placed on an east-west line through the crater center. One tower was on the crater floor, one was on the crater rim, two were on the east sidewall, and two were on the west sidewall. These sites measured components of the surface energy budget and the solar and terrestrial radiation budgets, and measured the strengths and directions of the up- and down-slope winds on the crater's sidewalls.

The IOP instruments included:

Three tethered balloon soundings systems. These sounding systems use an electric winch to pay line in or out allowing a helium-filled balloon that carries a meteorological instrument package (a 'sonde') to alternately ascend and descend through the depth of the crater. Vertical profiles of wind, temperature and humidity are transmitted to a ground receiving station during these ascents/descents. One sounding system was located in the center of the crater floor, one was partway up the east sidewall and the other was partway up the west sidewall. The soundings measured the basic mean and turbulent structures in the crater temperature inversion. Asymmetries in the crater inversion structure were determined from synchronous ascents of these balloons. Such asymmetries are a feature of the post-sunrise inversion breakup period when the sun shines more strongly on the west sidewall (i.e., east-facing sidewall) and the pre-sunset inversion buildup period when the sun shines more strongly on the west-facing sidewall.

Tethered balloon sounding system

Helium-filled tethered balloon used to carry meteorological instruments for making occasional vertical profiles of temperature, moisture and winds through the lower atmosphere. The balloon's altitude is controlled by an electric winch that pays out or brings in tetherline. The meteorological sonde on the tetherline is approximately 2.5 m below the balloon and transmits data to a ground receiving station inside the tent. When the balloon is in motion, the winch operator must very carefully monitor the balloon's progress from the lawn chair (NO sleeping!). If the winch operator is asleep at the switch, the balloon might descend all the way to the winch, breaking the tetherline and allowing the balloon and instruments to fly off into the wild blue yonder.

Tethered balloon being flown from a lawnchair in Peter Sinks, Utah

Tethered balloon being operated from a gasoline-powered generator and winch on the sidewall of Utah's Peter Sinks basin. Two other balloons were operated concurrently in this basin, with data from all three balloons being transmitted to a single ground station in a tent on the basin floor. © Craig Clements.

Educational Opportunities

During the experiment, we provided a poster at the Meteor Crater Museum to provide visitors information about the METCRAX experiment at the Meteor Crater's visitor center. A number of crater visitors in October 2006 stopped in to view our activities and read about our experiments and what we are learning about the meteorology of the crater! Access to the crater itself, however, was strictly limited to the research staff.

A number of university students working on thesis topics are using the data from the Meteor Crater experiments. Many helped us in the field experiments with the tethered balloon and rawinsonde launches. Several scientists on the research team were from other countries.

Photos

The Crater & Surroundings

Instrumentation

IOP number 1

IOP number 2

IOPs 3 & 4

Nature

People

Preparation & Setup

Towers and Sites

Outdoors, Food, Fun

Data

Meteorological data

Scientific results

Links

Meteor Crater Enterprises

Barringer Crater Company

Sharon Zhong's METCRAX website

Meteor Crater fly-by animations