Moisture transport in observations and reanalyses as a proxy for snow accumulation in East Antarctica

Atmospheric moisture convergence on ice sheets provides an estimate of snow accumulation, which is critical to quantifying sea-level changes. In the case of East Antarctica, we computed moisture transport from 1980 to 2016 in five reanalyses and in radiosonde observations. Moisture convergence in reanalyses is more consistent than net precipitation but still ranges from 72 to 96&thinsp;mm&thinsp;yr−1 in the four most recent reanalyses, ERA-Interim, NCEP CFSR, JRA 55 and MERRA 2. The representation of long-term variability in reanalyses is also inconsistent, which justified resorting to observations. Moisture fluxes are measured on a daily basis via radiosondes launched from a network of stations surrounding East Antarctica. Observations agree with reanalyses on the major role of extreme advection events and transient eddy fluxes. Although assimilated, the observations reveal processes that reanalyses cannot model, some due to a lack of horizontal and vertical resolution, especially the oldest, NCEP DOE R2. Additionally, the observational time series are not affected by new satellite data unlike the reanalyses. We formed pan-continental estimates of convergence by aggregating anomalies from all available stations. We found statistically significant trends neither in moisture convergence nor in precipitable water.</p

Experimental Verification Towards Feed-Forward Ground Motion Mitigation at ATF2

International audienceWithout counter measures, ground motion effects would deteriorate the performance of future linear colliders to an unacceptable level. An envisioned new ground motion mitigation method (based on feed-forward control) has the potential to improve the performance and to reduce the system cost compared to other proposed methods. For the experimental verification of this feed-forward scheme, a dedicated measurement setup has been installed at ATF2 at KEK. In this paper, the progress on this experimental verification is described. An important part of the feed-forward scheme could be already demonstrated, namely the prediction of the orbit jitter due to ground motion measurements

LHC Survey Laser Tracker Controls Renovation

The LHC survey laser tracker control system is based on an industrial software package (Axyz) from Leica Geosystems™ that has an interface to Visual Basic™, which we used to automate the geometric measurements for the LHC magnets. With the new version of the Leica software, this Visual Basic™ interface is no longerb available and we had to redesign the interface software to adapt to a PC-DMIS server that replaced the Axyz software. As this package is no longer supported, we have taken the decision to recode the automation application in LabVIEW. This presentation describes the existing equipment, interface and application showing the reasons for our decisions to move to PC-DMIS and LabVIEW. A comparison between the new and legacy system is mad

Magnetic Axis and Geometric Measurement for the LHC Cryomagnet

The LHC cryomagnets are made with several types of magnets which all need to be aligned. Both magnetic and geometric axis need to be well known before the installation in the LHC tunnel. These measurements require integrated controls for optical, magnetic and geometric measurements systems. The measurement sequence as well as the analysis should be adapted to each type of magnet. To perform the measurement, a mole, equipped with a reflector, a CCD camera and Hall probe sensors should be moved along the tubes of the 15 metres long dipole magnets and rotated around its axis. The geometrical measurements are made with an industrial Laser Tracker system. Homemade systems have been developed for the image and magnetic measurements. Each part can be driven separately and form the lower layer of the system. The control, as well as the interaction of these systems, has been integrated into a single system using UDP communication. The harmonic analysis allows verification of the quality and the orientation of the magnetic field of the magnet. The geometric measurement program has been designed as a master, thus controlling all sub-systems and the quality of the acquired data. In order to operate the magnetic and geometric measurement independently, a remote control application has been made. The structure of these two major parts, geometric and magnetic, has been designed so that new functionality can easily be added

Experimental Verification Towards Feed-Forward Ground Motion Mitigation at ATF2

International audienceWithout counter measures, ground motion effects would deteriorate the performance of future linear colliders to an unacceptable level. An envisioned new ground motion mitigation method (based on feed-forward control) has the potential to improve the performance and to reduce the system cost compared to other proposed methods. For the experimental verification of this feed-forward scheme, a dedicated measurement setup has been installed at ATF2 at KEK. In this paper, the progress on this experimental verification is described. An important part of the feed-forward scheme could be already demonstrated, namely the prediction of the orbit jitter due to ground motion measurements