Inhomogeneities Research Articles

Impact of missing data on the efficiency of homogenisation: experiments with ACMANTv3

The impact of missing data on the efficiency of homogenisation with ACMANTv3 is examined with simulated monthly surface air temperature test datasets. The homogeneous database is derived from an earlier benchmarking of daily temperature data in the USA, and then outliers and inhomogeneities (IHs) are randomly inserted into the time series. Three inhomogeneous datasets are generated and used, one with relatively few and small IHs, another one with IHs of medium frequency and size, and a third one with large and frequent IHs. All of the inserted IHs are changes to the means. Most of the IHs are single sudden shifts or pair of shifts resulting in platform-shaped biases. Each test dataset consists of 158 time series of 100 years length, and their mean spatial correlation is 0.68–0.88. For examining the impacts of missing data, seven experiments are performed, in which 18 series are left complete, while variable quantities (10–70%) of the data of the other 140 series are removed. The results show that data gaps have a greater impact on the monthly root mean squared error (RMSE) than the annual RMSE and trend bias. When data with a large ratio of gaps is homogenised, the reduction of the upper 5% of the monthly RMSE is the least successful, but even there, the efficiency remains positive. In terms of reducing the annual RMSE and trend bias, the efficiency is 54–91%. The inclusion of short and incomplete series with sufficient spatial correlation in all cases improves the efficiency of homogenisation with ACMANTv3.

Homogenization of precipitation time series with ACMANT

New method for the time series homogenization of observed precipitation (PP) totals is presented; this method is a unit of the ACMANT software package. ACMANT is a relative homogenization method; minimum four time series with adequate spatial correlations are necessary for its use. The detection of inhomogeneities (IHs) is performed with fitting optimal step function, while the calculation of adjustment terms is based on the minimization of the residual variance in homogenized datasets. Together with the presentation of PP homogenization with ACMANT, some peculiarities of PP homogenization as, for instance, the frequency and seasonal variation of IHs in observed PP data and their relation to the performance of homogenization methods are discussed. In climatic regions of snowy winters, ACMANT distinguishes two seasons, namely, rainy season and snowy season, and the seasonal IHs are searched with bivariate detection. ACMANT is a fully automatic method, is freely downloadable from internet and treats either daily or monthly input. Series of observed data in the input dataset may cover different periods, and the occurrence of data gaps is allowed. False zero values instead of missing data code or physical outliers should be corrected before running ACMANT. Efficiency tests indicate that ACMANT belongs to the best performing methods, although further comparative tests of automatic homogenization methods are needed to confirm or reject this finding.

A symmetry break in dynamo models

In accordance with the concepts of dynamo theory, largescale magnetic fields of many astrophysical objects are associated with the rotationinduced break of mirror symmetry (1). The rotation of objects and the presence of depth density gradients (∇ρ) turn out to be sufficient for the existence of a correlation between the vertical velocity and the vorticity of small� scale vortices. This correlation results in the nonzero kinetic helicity χ = 〈v · rotv〉, where v is the turbulent velocity and 〈·〉 implies averaging over an ensemble. In the simplest cases, it is considered that, in the same hemisphere, the helicity is of identical sign: in the northern hemisphere, it is negative when the density increases with depth, which is natural for selfgravitat� ing bodies. In the southern hemisphere, the helicity is positive, e.g., χ = -cosϑ (2, 3), where ϑ is the angle with respect to the rotation z axis in the spherical coor� dinate system (r, ϑ, ϕ). The existence of the nonzero helicity χ of the hemispheres significantly simplifies the generation of a largescale magnetic field. At the same time, the helicity is obtained as a result of aver� aging and is subjected to random fluctuations (4), which, in the long run, affects the generation of the magnetic field (5). The source of the fluctuations can be either an insufficient number of vortices over which averaging is performed or the existence of anomalies at the object boundaries, e.g., the appearance of tidal forces in binary stars or the presence of thermal inho� mogeneities at boundaries of the liquid core and the mantle in planets (6). These arguments can lead to the break of antisymmetry χ with respect to the equatorial plane. In the framework of the Parker model for the αω dynamo, we show below that, even for a linear mode, a small nonparity (χ) violation can lead to a sig� nificant symmetry break of the magnetic field in oppo� site hemispheres. We now consider the Parker model often applied to describe processes of the magneticfield generation in various astrophysical objects (1, 7, 8). We below make use of the following equations in a thin spherical shell:

Newest developments of ACMANT

Abstract. The seasonal cycle of radiation intensity often causes a marked seasonal cycle in the inhomogeneities (IHs) of observed temperature time series, since a substantial portion of them have direct or indirect connection to radiation changes in the micro-environment of the thermometer. Therefore the magnitudes of temperature IHs tend to be larger in summer than in winter. A new homogenisation method, the Adapted Caussinus – Mestre Algorithm for Networks of Temperature series (ACMANT) has recently been developed which treats appropriately the seasonal changes of IH-sizes in temperature time series. The performance of ACMANT was proved to be among the best methods (together with PRODIGE and MASH) in the efficiency test procedure of COST ES0601 project. A further improved version of the ACMANT is described in this paper. In the new version the ANOVA procedure is applied for correcting inhomogeneities, and with this change the iterations applied in the earlier version have become unnecessary. Some other modifications have also been made, from which the most important one is the new way for estimating the timings of IHs. With these modifications the efficiency of the ACMANT has become even higher, therefore its use is strongly recommended when networks of monthly temperature series from mid- or high geographical latitudes are subjected to homogenisation. The paper presents the main properties and the operation of the new ACMANT.

Kinematic Isotropy and the Conditioning Index of Serial Robotic Manipulators

The conditioning index of a serial robotic manipulator is de fined in this article in terms of the reciprocal of its minimum condition number. The condition number of a manipulator is defined, in turn, as that of its Jacobian matrix. Moreover, in defining the Jacobian condition number, a quadratic norm of the Jacobian matrix is needed. However, this norm, or for that matter any other norm, brings about dimensional inho mogeneities. It is shown here that by properly defining the said norm based on a weighting positive definite matrix, the dimensional inhomogeneity is resolved. Manipulators with a conditioning index of 100% are termed isotropic, a six-axis isotropic manipulator being introduced. This manipulator has all its angles between neighboring revolute axes at 90° and all its distances between neighboring axes identical; more over, these distances are identical to the offsets of those axes. The kinematic conditioning of wrist-partitioned manipulators is given due attention, and illustrated with some examples of industrial robots of this type.

Singularities of the temperature dependence and optical quenching of the photocurrent and their relation to electrical inhomoge neities in zinc selenide single crystals

Singularities of the temperature dependence and optical quenching of the photocurrent and their relation to electrical inhomoge neities in zinc selenide single crystals

Comments on use of anomalous stations for IMS

One of us has recently reviewed the general problem of the effects of induction in the earth upon the measurement of external time‐varying magnetic fields [Gough, 1974]. In this context we are concerned about the inclusion of Rapid City, South Dakota, and Alert and Mould Bay, N.W.T., Canada, in magnetometer networks for the International Magnetospheric Study, as described by Lanzerotti et al [1976]. Inhomogen eities in the electrical conductivity of the earth's crust cause drastic distortions in the variation fields recorded at these stations.Rapid City is on top of an anomaly which more than doubles the D component variations, at periods of tens of minutes; Zis also anomalous [Alabi et al., 1975]. At Alert the horizontal variation vector is strongly confined in the northwest‐southeast direction [Niblett et al., 1974]. Observations at Rapid City and Alert will certainly be dominated by the very large anomalies caused by induced currents channeled in the underlying crust. At Mould Bay the vertical variations are unusually attenuated by crustal layers of anomalously high conductivity [DeLaurier et al., 1974].