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Persistence of systematic errors in the Asian-Australian monsoon precipitation basic states in climate models: a way forward
The annual cycle of the Asian-Australian monsoon (AAM) system can be regarded as the seasonal displacement of the large-scale Intertropical Convergence Zone (ITCZ), which is anchored by the north-south migration of the Indo-Pacific warm pool. In the respective hemispheres, intense solar heating over land during spring and early summer provide the necessary thermodynamic conditions for the occurrence of deep convection off the equator. The rainfall and diabatic heating associated with the AAM is perhaps the most vigorous of all the regional monsoon components in the globe. Yet, skill in monsoon prediction (days to seasons) by dynamical models remains low, partly due to our lack of understanding of the entirety of the monsoon system and our inability to model the interactive processes that govern it. Simulating the monsoon precipitation climatology remains a grand challenge. The multi-model mean (MMM) errors for summertime precipitation relative to GPCP observations have shown little improvement in CMIP5 as compared to CMIP3. For the Asian Summer Monsoon, the MMM monsoon rainfall is weaker over South Asia, the western equatorial Indian Ocean and tropical West Pacific. For the Australian summer monsoon, it is excessive over most of the Maritime Continent, and deficient over northern Australia. Throughout the year, excessive rainfall is simulated over South China Sea – Maritime Continent regions, and CMIP5 models do not capture the annual cycle of the AAM. One implication is that uncertainties in future projections (e.g., IPCC 2013) of AAM mean rainfall may not have reduced from CMIP3 to CMIP5. Solutions from an intermediate model show that diabatic heating (Q) associated with the AAM influences the global circulation. Compared to the reanalysis, many models tend to have maxima at the mid-troposphere but their simulated amplitude is overestimated in the lower troposphere (900-700 hPa) and underestimated from 600-300 hPa, a feature readily apparent in the MMM composite (dashed black line). The lower troposphere peak may be attributed to misrepresentations in shallow convection. Some outliers, such as CSIROMk3- 6-0 and ACCESS1-3, do not show any appreciable vertical structure, and the simulated monsoon over South Asia is virtually absent in these models. TRMM observations indicate that over the monsoon region the contribution from stratiform rainfall is about 40% to the Q intensity. In contrast, most of the CMIP3 models produce too much convective rainfall (95% of the total) and too little stratiform precipitation. Given the persistence of errors, we speculate that errors in the partitioning of total rainfall into convective-stratiform still persist in CMIP5, and may be one of the reasons for underestimation (overestimation) of Q in the layer 600-300 (900-700) hPa. In summary, the rather slow progress in modeling in the last decade or so led us to wonder: Has the scientific community reached a “plateau” in modeling mean monsoon precipitation?
A systematic error affecting NER calculations
Factors that may affect the precision of Neutron Emission Rate (NER) measurements made in the Canberra 4 neutron counter have been examined and quantified. Measurements of sample NER are corrected for the efficiency of the counter. The efficiency is calculated by measuring a source of known intensity, and taking the ratio of the measured neutrons per second (n/s) to the known output of the source.
Assessing Systematic Errors in Simulation Studies of Mu2e
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Systematic errors in Hadamard transform optics
Error sources encountered in Hadamard transform optical instruments are discussed. Such errors are caused by factors including moving masks, incorrect mask alignment, defects in mask fabrication, missing data, drifts in background level, and diffraction. Techniques for error reduction and/or elimination are described for each of the cases considered. It is noted that the errors described occur in singly encoded spectrometers and imagers.
The impact of satellite sounding data on the systematic error of a NWP model
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Systematic Errors in Stereo PIV When Imaging through a Glass Window
This document assesses the magnitude of velocity measurement errors that may arise when performing stereo particle image velocimetry (PIV) with cameras viewing through thick, refractive window and where the calibration is performed in one plane only. The effect of the window is to introduce a refractive error that increases with window thickness and the camera angle of incidence. The calibration should be performed while viewing through the test section window, otherwise a potentially significant error may be introduced that affects each velocity component differently. However, even when the calibration is performed correctly, another error may arise during the stereo reconstruction if the perspective angle determined for each camera does not account for the displacement of the light rays as they refract through the thick window. Care should be exercised when applying in a single-plane calibration since certain implicit assumptions may in fact require conditions that are extremely difficult to meet in a practical laboratory environment. It is suggested that the effort expended to ensure this accuracy may be better expended in performing a more lengthy volumetric calibration procedure, which does not rely upon the assumptions implicit in the single plane method and avoids the need for the perspective angle to be calculated.
Global-scale signals and systematic errors in GPS site height time series
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Contribution of Modeling Differences to Systematic Errors of the Celestial Reference Frame: Modest/Calc/Gloria
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Systematic Errors in Current Extragalactic Radio Source Catalogs
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Systematic Error Analysis for GPS RO Refractivity in the Lower Troposphere
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ASSESSMENT OF SYSTEMATIC CHROMATIC ERRORS THAT IMPACT SUB-1% PHOTOMETRIC PRECISION IN LARGE-AREA SKY SURVEYS
Meeting the science goals for many current and future ground-based optical large-area sky surveys requires that the calibrated broadband photometry is both stable in time and uniform over the sky to 1% precision or better. Past and current surveys have achieved photometric precision of 1%–2% by calibrating the survey’s stellar photometry with repeated measurements of a large number of stars observed in multiple epochs. The calibration techniques employed by these surveys only consider the relative frame-by-frame photometric zeropoint offset and the focal plane position-dependent illumination corrections, which are independent of the source color. However, variations in the wavelength dependence of the atmospheric transmission and the instrumental throughput induce source color-dependent systematic errors. These systematic errors must also be considered to achieve the most precise photometric measurements. In this paper, we examine such systematic chromatic errors (SCEs) using photometry from the Dark Energy Survey (DES) as an example. We first define a natural magnitude system for DES and calculate the systematic errors on stellar magnitudes when the atmospheric transmission and instrumental throughput deviate from the natural system. We conclude that the SCEs caused by the change of airmass in each exposure, the change of the precipitable water vapor and aerosol in the atmosphere over time, and the non-uniformity of instrumental throughput over the focal plane can be up to 2% in some bandpasses. We then compare the calculated SCEs with the observed DES data. For the test sample data, we correct these errors using measurements of the atmospheric transmission and instrumental throughput from auxiliary calibration systems. The residual after correction is less than 0.3%. Moreover, we calculate such SCEs for Type Ia supernovae and elliptical galaxies and find that the chromatic errors for non-stellar objects are redshift-dependent and can be larger than those for stars at certain redshifts.
First Simultaneous Determination of Inclusive and Exclusive | V u b |
The first simultaneous determination of the absolute value of the Cabibbo-Kobayashi-Maskawa matrix element V ub using inclusive and exclusive decays is performed with the full Belle data set at the $Υ$(4S) resonance, corresponding to an integrated luminosity of 711 fb -1 . We analyze collision events in which one B meson is fully reconstructed in hadronic modes. This allows for the reconstruction of the hadronic X u system of the semileptonic b → $πℓe_ℓ$ decay. We separate exclusive B → $πℓ\overline{ν}_ℓ$ decays from other inclusive B → $X_uℓ\overline{ν}_ℓ$ and backgrounds with a two-dimensional fit that utilizes the number of charged pions in the X u system and the four-momentum transfer q 2 between the B and X u systems. Combining our measurement with information from lattice QCD and QCD calculations of the inclusive partial rate as well as external experimental information on the shape of the B → $πℓe_ℓ$ form factor, we determine |$V^{excl}_{ub}$| = (3.78 ± 0.23 ± 0.16 ± 0.14) × 10 -3 and |$V^{incl}_{ub}$| = (3.88 ± 0.20 ± 0.31 ± 0.09) x 10 -3 , respectively, with the uncertainties being the statistical error, systematic errors, and theory errors. The ratio of |$V^{excl}_{ub}$|/|$V^{incl}_{ub}$| 0.97 ± 0.12 is compatible with unity.
On the accuracy and precision of extinctions derived from general star counts
The accuracy and the applicability of the method of general star counts are discussed. The effects of statistical errors, pseudorandom errors, systematic errors, and sampling errors are considered. The conditions under which quantitatively useful results can be derived are identified. It is found that for plates reaching 17th to 20th mag, general star counts can be a useful technique for investigating the structure of dark cloud complexes located within 500 to 1000 pc of the sun.