METCRAX The Meteor Crater Experiment An Upcoming Study of Cold Air Pools and Seiches in Arizona’s Meteor Crater Good afternoon. I would like to talk to you this afternoon about an upcoming study called METCRAX of cold pools and seiches in Arizona’s Meteor Crater, which you see in the background there. Maura Hahnenberger and C. David Whiteman, University of Utah Andreas Muschinski, U of Mass Amherst Sharon Zhong, University of Houston David C. Fritts, Northwest Research Associates, Inc. © John S. Shelton

METCRAX overview 3 year meteorological research program supported by NSF grants NCAR field support PIs: Andreas Muschinski, Dave Fritts, Dave Whiteman, Sharon Zhong Field phase: October 2006 Continuous measurements during month ~8 intensive observational periods (IOPs) in which tethersondes and rawinsondes will be flown Numerical modeling and analysis METCRAX will be a three year program supported by NSF and NCAR, with PIs Andreas Muschinski, Dave Fritts, Dave Whiteman, and Sharon Zhong. The field phase of this project will occur during October of 2006 and will include both continuous measurements throughout the month and about 8 IOPs when tethersondes and rawinsondes will be flown. In addition to the field program there will be numerical modeling done of the crater boundary layer.

METCRAX Objectives Seiches & Internal Waves Determine the role played in transport and mixing in basin stable layers Temperature Inversions & Cold Air Pools Investigate the diurnal buildup and breakdown and the associated physical and dynamical processes The two main objectives of the program are to determine the role that basin-scale seiches and internal waves play in transport and mixing in the basin stable layers and also to investigate the diurnal buildup and breakdown of basin termperature inversions or cold air pools and the associated physical and dynamical processes.

Motivation Inversion Evolution Physical processes are poorly understood in complex terrain Leading forecast problem in the Western US Improved understanding may lead to better forecasts Understanding of physics may be easier in simple laboratory-like conditions The motivations for this research program are that the physical processes leading to inversion evolution are poorly understood in complex terrain. Valley and basin inversions continue to be a leading forecast problem in the western US, in a large part because of our constrained understanding of factors leading to cold pool buildup and breakup. Improving our understanding of the basic physics of this process will hopefully lead to better forecasts in the future. Furthermore, in the past cold pools have been studied in valleys and basin with complex terrain. In this study we hope that by using a simpler laboratory-like setting, it may be easier to understand the physics of the process.

No large-scale advection Why the Meteor Crater? So, what do we mean by a laboratory-like setting. We chose the Arizona Meteor Crater because of it’s simplified topography. The area surrounding the crater is a flat plain. The crater itself is bowl shaped, nearly symmetric, and has a uniform rim height. This leads to limited large scale advection into the crater. The crater is at 1.2 km wide and 175 m deep is also the right size for this type of study, being large enough to have a significant cold pool protected from the direct effects of large-scale advection while also small enough to allow the coriolis force to be ignored. Furthermore, the crater is small enough to instrument effectively and economically. On a flat plain Uniform rim height No large-scale advection The right size

Seiches/Gravity Waves Basin cold pools can exhibit oscillations similar to a basin of water Seiches have been observed in lake basins Have not yet been studied in atmosphere A cold-air pool in a basin is similar to a basin of water and both can exhibit oscillations. A seiche is like a trapped standing wave in a basin. A simplified way to imagine a seiche is if you have a cup of tea and tilt the cup and let the water slosh back and forth. In the atmosphere it is the winds above the basin that initiate these waves. This type of oscillation has been observed in lake basins, but has yet to be studied in atmospheric cold pools.

Cold Pool Buildup/Breakup Determine physical processes that govern buildup/breakup Slope flows Radiative transfer (long- and short-wave) Turbulent transfer Asymmetries in BL structure and evolution Ambient flows above basin The other main scientific objective of the program is to determine the physical processes that govern buildup and breakup of the basin cold pool. Known factors in this process include slope flows, long- and short-wave radiative transfer, turbulent transfer, asymmetries in the boundary layer structure and evolution, and the ambient flows above the basin. The instrumentation planned for the studies attempts to capture all of these factors in order to gain a complete view of the boundary layer evolution in the crater.

Preliminary Measurements Here we have some preliminary results from October of this year. The blue line is the temperature on the rim of the crater, while the green line is the temperature on the floor of the crater. You can see that consistently the low temperature at the floor of the crater is colder than the rim by around 5-8 degrees Celsius. From these results we can see that the crater does indeed have a diurnal cold air pool. Crater Rim & Floor Temperatures, Oct. 2005

Tethered balloon sounding system Instrumentation Tethered balloon sounding system HOBO ISFF ISS Here we see the planned instrumentation for the crater. To monitor the background meteorology above and upwind of the crater we will place an Integrated Sounding System or ISS within about 10 km of the crater. This will collect wind profiles, and use a Radio Acoustic Sounding System to collect virtual temperature profiles outside the crater. Also at this site will be an Integrated Surface Flux Facility or ISFF to measure surface fluxes outside the crater. The six remaining ISFFs will be placed in an west to east line across the crater including sitings on the rim, slopes, and crater floor. The ISFFs will be used to detect seiches, measure the slope flow characteristics, and measure the surface energy budgets at various locations in the crater. The dashed lines indicate the locations of the 50 HOBO temperature sensors, with 25 on a north-south line and 25 on and east-west line. With these sensors we will monitor the cross-crater variations in one meter air temperature. Additionally, during the cold pool buildup and breakup periods three tethersondes, indicated by the Xs, will be flown concurrently to measure the evolving wind, temperature, and humidity profiles in the crater. (triangle) 1 ISS - (dashed lines) 50 HOBOs - (square) 7 ISFFs - (X) 3 tethersondes

Field Plan: 1-31 October 2006 Continuous observations: Outside the Crater Radar profiler/RASS Doppler sodar/RASS Weather station, 1 ISFF tower, HOBOs Inside the Crater 6 ISFF towers - 5 on slopes, 1 on rim HOBOs, N-S and E-W lines across crater Special IOP operations: Rawinsondes at 3-h intervals Tethered balloon soundings, 3pm to 10am to 325 m During the field project we will have continuous observations, both inside and outside the crater. To measure the background meteorology outside the crater we will have a radar profile, RASS, doppler sodar, a surface weather observing station, an ISFF tower and HOBO temperature sensors. Inside the crater there will be six ISFF towers and additional HOBOs in N-S and E-W lines across the crater. With these continuous observations we will observe the diurnal boundary layer structure inside and outside the crater in addition to detecting seiches and gravity waves with high frequency observations. During the IOP operations we will have additional rawinsonde flights at three hour intervals outside the crater, and tethersonde flights within the crater. The IOP operation will be more focused on looking at the cold pool in the crater, and especially the build-up and break-up periods. The field plan is designed to observe the boundary layer inside and outside the crater completely in order to more fully understand the physics governing its evolution.

Questions? Thank you, and I’ll take any questions. © John S. Shelton