CosmOz newsletter, February 2013
This month we announce the upcoming CosmOz workshop in Brisbane, talk about simple corrections to cosmic ray neutron data to account for changes in cosmic ray intensity and update you on recent progress in continental scale soil moisture mapping from cosmic-ray probes in the US.
Planning is now underway for a CosmOz workshop in Brisbane on the 22nd and 23rd of May. The aim is to get interested parties and probe managers together to talk about where we have got to with the CosmOz network over the last couple of years. Topics to be discussed include interesting data sets and analysis, calibration progress, linkages to other projects, data delivery, future research direction and funding opportunities.
We have been fortunate enough to receive funding from CSIRO’s Earth Observation & Informatics-Transformational Capability Platform which will help us to bring world leaders from the US COSMOS network to Australia to share their experience and expertise. This funding will also help to cover workshop costs and provides an excellent opportunity for interested parties to come together and discuss the exciting scientific opportunities around the cosmic-ray probe.
Cosmic-ray dosage corrections
Last issue we talked about the need to apply simple corrections to cosmic ray neutron count data to account for the effects of atmospheric pressure change (particularly when cyclones occur!), this issue we will discuss the simple corrections which are required to account for changes in background levels of incoming cosmic-rays. Temporal variations in high energy cosmic ray neutrons at the Earth’s surface are mainly caused by solar activity. During high solar output (solar maximum) the solar magnetic field is stronger and deflects a greater proportion of incoming cosmic rays away from the Earth. The opposite occurs during periods of low solar output (solar minimum). The cycle of solar minimum and solar maximum occurs over a period of roughly 11 years. In addition to this cyclic effect there are also short-term fluctuations, such as solar flares, which effect the relative level of incoming cosmic-ray neutrons. An example of the effect of a solar flare that occurred early in 2012 on cosmic ray dosage is shown in Figure 1. A simple correction to dosage rates on a reference date (usually when the probe was calibrated) is all that is required to remove background dosage effects. Temporal variations in cosmic-ray dosage are measured using devices known as neutron monitors which measure high-energy secondary neutrons which are insensitive to local factors such as soil moisture. A number of these sensors are located around the world (see database here) including one in Kingston near Hobart which is maintained by the BoM Space Weather services.
Figure 1. The effect of the solar flare in early 2012 on cosmic-ray dose rate. Simple corrections are applied to remove this variation from the cosmic-ray probe data. Data from neutron monitor station in Yakutsk, Russia.
Continental US soil moisture maps derived from cosmic-ray probes
The COSMOS network in the USA have recently added the ability to produce maps of soil moisture for Continental US to their impressive website. An example map is shown in Figure 2. The utility can be found at this URL:
The mapping product utilises the existing calibrated probes but the potential to improve this product as the US network plans to expand to 500+ cosmic-ray probes is clear. Such a product could be used in numerous applications and we think this is a very nice example of what is possible with the comic-ray probe network. The website also offers the ability to subtract the soil moisture at one time-step from another to display relative changes between time periods.
Figure 2. Soil wetness map produced for the Continental US based on the existing COSMOS network.
New papers recently published:
· Shuttleworth, J., R. Rosolem, M. Zreda and T.E. Franz. The COsmic-ray Soil Moisture Interaction Code (COSMIC) for use in data assimilation, Hydrology and Earth System Sciences Discussions 10, 1097-1125,doi:10.5194/hessd-10-1097-2013.
· Franz, T.E, M. Zreda, R. Rosolem and T.P.A. Ferre, 2013. A universal calibration function for determination of soil moisture with cosmic-ray neutrons, Hydrology and Earth System Sciences 17, 453-460,doi:10.5194/hess-17-453-2013.
Recently submitted paper:
· McJannet, D., Hawdon, A., Zreda, M., Franz, T., Chrisman, B. Submitted. Soil moisture measurements at an intermediate scale using cosmic-ray neutrons. IGARRS, IEEE International Geoscience and Remote Sensing Symposium
Melbourne, July 2013.
N.B. the US based COSMOS team host a regularly updated list of cosmic-ray probe related publications. Those interested can find publications and links here: http://cosmos.hwr.arizona.edu/Docs/index.html
All the best for 2013,
Dave McJannet and Aaron Hawdon