Department of Hydrology and Water Resources and Department of Atmospheric Science

1. The COsmic-ray Soil Moisture Observing System (COSMOS):New opportunity to explore carbon/water cycle links at AMERIFLUX sites W. James Shuttleworth, MarekZreda, XubinZeng, Chris Zweck, Ty P.A. Ferré and Rafael Rosolem Department of Hydrology and Water Resources and Department of Atmospheric Science University of Arizona, USA With acknowledgements to: Darin Desilets, Amy Rice, Russ Scott, and Chawn Harlow NSF, Army Research Office, and UA Water Sustainability Program Hydroinnova, Zetetic Institute, Quaesta Instruments, General Electric, and PDT (The Hydroinnova Consortium)

2. A (Very) Brief Overview of COSMOS • The need for plot average soil moisture measurements • How does the COSMOS soil moisture probe work? • COSMOS project plans in the next year • Observational partnership with AMERIFLUX

3. Meteorological need for soil moisture measurements Hypothesis: water stored in the soil which entered from earlier precipitation can subsequently be made accessible to the atmosphere (often via plants) and influence the weather for several months by: • contributing to the water available for precipitation (recycling) • regional modification of downwind structure of the atmosphere • generating mesoscale circulations Evidence in hydro-climate records Soil Saturation condition ahead of summer rain Lagged correlation between soil moisture and precipitation in Illinois (Findell & Eltahir, 1997)

4. Meteorological need for soil moisture measurements Height Height Environmental adiabatic lapse rate Moist adiabatic lapse rate Cloud Cloud Dry adiabatic lapse rate Potential Temperature Potential Temperature Upgrade of ECMWF land model gave more realistic precipitation Mississippi Floods in 1993 - model Influence not through recycling, rather through modified downwind lapse rate (Beljaars, Betts etc, 1990s) Mississippi Floods in 1993 - observation

5. Meteorological need for soil moisture measurements The Global Land-Atmosphere Coupling Experiment (GLACE) Average for 8 “best” models GCM evidence of the influence of soil moisture status on seasonal climate

6. Hydrological need for soil moisture measurements Sample sub-catchments using a moveable probe COSMOS Probe • Soil moisture patterns in catchment hydrology to study: • Their relationship to topography, soil depth, bedrock, permeability, and their covariance • Their rate of change from wet state to a dry state • Their value as an additional model calibration objective function • Their links to GRACE satellite studies • ……..etc……..

7. Eco-hydrological need for soil moisture measurements • Fundamentally based on the common stomatal pathway for CO2 and H2O flux • Facilitated by the footprint for eddy flux and COSMOS probe measurements being about the same size

8. How do COSMOS Probes Measure Soil Moisture? Neither the basic idea nor basic sensor technology is new (important from standpoint of “readiness”) Neutron detectors have been around since the 1950s. They are simple, robust, and stable, and are now available “off the shelf”. The fact that surface moisture can alter the measured above-ground neutron count rate was known in the 1960s (and considered a nuisance!) • What is New? • systematic understanding of • cosmic-ray neutron interactions at • the ground-atmosphere interface • (based on measurements and • modeling) that identified the near- • surface above-ground fast neutron • density has: • a source footprint of hectometers • limited sensitivity to soil type • improved and low power electronics • (for pulse shaping and amplification; • remote detection and correction of • sensor drift, and remote data capture); • and better (solar) power systems Hendrick and Edge (1966) Cosmic-ray neutrons near the Earth Physical Review Series II, 145:1023-1025. Water Moist soil Dry soil

9. How do COSMOS Probes Measure Soil Moisture? How are high energy neutrons created in the soil? IN SPACE: there are incoming high-energy cosmic-ray protons Their intensity changes slowly with time, and with geomagnetic latitude, (because they interact with the Earth’s magnetic field). These both have to be corrected for in COSMOS Relative “slowing” power IN THE ATMOSPHERE: cascades of secondary cosmic rays are generated The intensity of these cascades depends on barometric pressure. This has to be corrected for in COSMOS Hydrogen IN THE SOIL: the fast neutrons are scattered (“thermalized”) and absorbed BUT some escape back into the air above the ground, depending on the composition of the soil, especially on its water content (strictly hydrogen content) Relative absorbing power Hydrogen

10. How do COSMOS Probes Measure Soil Moisture? How does neutron count rate respond to soil moisture? Monte-Carlo Simulation of Neutron Density This is largely a soil-dependent “shift”, SO ONLY ONE FIELD CALIBRATE NEEDED In drier soil, more neutrons escape Monte-Carlo Simulation of Neutron Density COSMOS probes detect neutrons at two energies, but use “fast” neutrons for soil moisture detection because calibration is less sensitive to the chemistry of the soil (thermal neutrons give information on above-ground water, e.g. snow cover) Fast Neutron Detector In moister soil, less neutrons escape Thermal Neutron Detector

11. How do COSMOS Probes Measure Soil Moisture? Over what soil volume does the COSMOS probe measure? Move sensor away from coast Measurement Volume (modeled by tracking neutron collisions) Depth Radius Approximate check on radius - move sensor away from the coast in Hawaii 86% of neutrons from within a depth of 70 cm (dry) Depth decreases to 12 cm in wet soils Independent of altitude (and pressure) 86% of neutrons from within a radius of 350 m Independent of soil moisture Increases with increasing altitude (decreasing pressure) Modeled relationship Relative number of counts Measured Count Rates

12. How do COSMOS Probes Measure Soil Moisture? Example COSMOS Data for the San Pedro Basin Gravimetric samples are in red, with sampling error Soil moisture from cosmic-ray neutron data compared with gravimetric samples How many point measurements are needed to get a similar (2%) precision in area-average soil moisture? For the (single) calibration of a COSMOS probe (made at installation), soil will be sampled at 3 depths, 8 directions, and 3 radii around the probe (i.e., 72 samples). Diurnal Cycles (moisture redistribution)

13. Looking to the Future Large Scale COSMOS Deployments at up to 500 Sites

14. COSMOS Project Deployment Plans • COSMOS approved by NSF for 4 years (Sept 2009 – Aug 2013) operating in • “proof of concept and demonstration of data utility mode” • Opportunity for a (10-fold?) expanded national network of COSMOS probes thereafter, subject to success in this initial phase • 50 COSMOS probes will be deployed by the end of 2011 at sites selected to • provide maximum benefit to the scientific community • effectively demonstrate the value of this new measuring method • Need sites with ancillary open source meteorological data and fluxes AMERIFLUX sites Jan 2011 May 2011 Note additional AMERIFLUX sites (mainly Tilden Myers Currently Deployed Probes Additional Near-term Deployments

15. COSMOS Project Deployment Plans Additional AMERIFLUX Sites where COSMOS might be deployed this year By Dec 2011

16. COSMOS Project Deployment Plans Additional AMERIFLUX Sites where COSMOS might be deployed this year By Dec 2011 2? 3+? 5+? 2? 3+? 2+? 2+? ~25 Total

17. Bottom Line • The COsmic-ray Soil Moisture Observing System (COSMOS) Project is urgently soliciting expressions of interest in collaborative research at AMERIFLUX sites to explore carbon/water cycle linkages • Must have publicly available measurements of meteorological variables and water vapor and CO2 fluxes • If interested, please: • take and complete an “expression of interest” form, and; • contact Rafael Rosolem <rosolem@email.arizona.edu> ~25 Total