On depth and temperature biases in bathythermograph data: Development of a new correction scheme based on analysis of a global ocean database

The World Ocean Database 2005 as of May 2009 is used to estimate temperature and sample depth biases of expendable (XBT) and mechanical (MBT) bathythermographs by comparing bathythermograph temperature profiles with more accurate bottle and conductivity/temperature/depth (CTD) data. It is shown that the application of depth corrections estimated earlier from side-by-side XBT/CTD inter-comparisons, without accounting for a pure thermal bias, leads to even larger disagreement with the CTD and bottle reference temperatures. Our calculations give evidence for a depth-variable XBT fall-rate correction with the manufacturer-derived depth being underestimated in the upper 200 m and overestimated below this depth. These results are in agreement with side-by-side inter-comparisons and direct fall-rate estimates. Correcting XBT sample depths by a multiplicative factor which is constant with depth does not allow an effective elimination of the total temperature bias throughout the whole water column. The analysis further suggests a dependence of the fall rate on the water temperature which was reported earlier in the literature. Comparison among different correction schemes implies a significant impact of systematic biases on the estimates of the global ocean heat content anomaly.     

Tracing glacier wastage in the Northern Tien Shan (Kyrgyzstan/Central Asia) over the last 40 years

The status and dynamics of glaciers are crucial for agriculture in semiarid parts of Central Asia, since river flow is characterized by major runoff in spring and summer, supplied by glacier- and snowmelt. Ideally, this coincides with the critical period of water demand for irrigation. The present study shows a clear trend in glacier retreat between 1963 and 2000 in the Sokoluk watershed, a catchment of the Northern Tien Shan mountain range in Kyrgyzstan. The overall area loss of 28% observed for the period 1963–2000, and a clear acceleration of wastage since the 1980s, correlate with the results of previous studies in other regions of the Tien Shan as well as the Alps. In particular, glaciers smaller than 0.5 km² have exhibited this phenomenon most starkly. While they registered a medium decrease of only 9.1% for 1963–1986, they lost 41.5% of their surface area between 1986 and 2000. Furthermore, a general increase in the minimum glacier elevation of 78 m has been observed over the last three decades. This corresponds to about one-third of the entire retreat of the minimum glacier elevation in the Northern Tien Shan since the Little Ice Age maximum.     

Palaeomagnetic data from Ediacaran (Vendian) sediments of the Arkhangelsk region, NW Russia: An alternative apparent polar wander path of Baltica for the Late Proterozoic–Early Palaeozoic

The study area is situated along the Zolotica river in NW Russia, located within the Kola–Dvyna Rift System in the Baltic Shield that developed during Meso and Neoproterozoic times. A 9-m thick section made up of shallow marine sediments of Upper Ediacaran age was sampled in this locality. Two volcaniclastic levels from the middle part of the section yielded an age of 556 Ma. (U/Pb SHRIMP-II on zircons). Two magnetic components were successfully isolated, component A (Decl = 157.1, Incl = 68.0, ₉₅ = 1.9°, N = 575 in situ) carried by magnetite and component B (Decl = 120.3, Incl = − 31.7, ₉₅ = 3.9°, N = 57, bedding corrected), carried by haematite. While component A is thought to represent a younger overprint direction, the in situ direction for component B on the other hand, is dissimilar to any expected younger direction and is considered to be primary magnetisation in origin, acquired during or soon after deposition of the sediments in the Late Ediacaran. The corresponding palaeomagnetic pole for component A in situ is located at Lon = 55.4°E, Lat = 31°N, A₉₅ = 2.7° and for component B at Lon = 110°E, Lat = 28.3°S, A₉₅ = 3.8°, N = 57. Combined with other palaeomagnetic poles of the same tectonostratigraphic unit an alternative apparent polar wander path for the Late Proterozoic–Early Palaeozoic of Baltica is proposed. Such an alternative path shows that after the mid Cryogenian (750 Ma), the poles that were situated over South Africa (p.d.c.) moved to the east until they reached Australia during the Late Ediacaran (555 Ma) where they remained approximately stationary until the beginning of the Cambrian (545 Ma). Finally, they moved to the northwest until they reached the Arabian Peninsula in the Early Ordovician. Palaeolatitudes indicate that Baltica situated near the equator from the Cryogenian through to the Ediacaran moving gradually to the south at c. 1 cm/yr. During the Late Early Ediacaran, the plate suddenly began to drift northward at c. 8 cm/yr and in the boundary with the Cambrian it was positioned in low to intermediate latitudes. Finally, Baltica began to move back to the south at c. 13 cm/yr until in the Early Ordovician, reaching intermediate to high southern latitudes.     

Radar measurements of integral parameters of hailstorms used on hail suppression projects

The exact quantitative estimation of hailstorm precipitation intensity, allowing determining successfully the crop hail damage, is extremely necessary while carrying out of programs of experimental researches of the hail clouds as well as at realization of operative projects on hail suppression. On the other hand, the possibility of obtaining a trustworthy information about changes of hailfall intensity during cloud seeding operations enables to judge more objectively about seeding effect and to make a decision about its beginning and termination. Just because of such a parameter, the kinetic energy of hailfalls presents a great interest for the researchers. As it is known, measuring the kinetic energy of hailfalls is carried out both directly by ground network of hailpads, and by radar methods. The accuracy of the radar methods of the hail kinetic energy measurement strongly depends not only on the choice of an optimum formula for calculation but also on the algorithm used for separating hail and rain parts of radar echo and on the way it was used in the hail–rain mixture zone of precipitation.The method of calculating the kinetic energy of the hailfalls, based on empirical dependence of hail probability P_h on a height of a zone of a radar echo with a reflectivity of 45 dBZ above a level of zero isotherm ΔH₄₅, is offered in the given work. The algorithm of separating hail and rain parts of a radar echo and the way it was applied in a hail–rain mixture zone is described. The examples of hail streaks in contours of radar reflectivity and in isopleths of hail kinetic energy obtained using the given algorithm are shown.In Mendoza province (Argentina), a hail suppression project (1993–1997) for the analysis of the vertical structure of a radar echo with Z_max > 45 dBZ, such new parameter is an integral altitude, was used. This dimensionless parameter is most sensitive to such a condition of radar echo when all four contours of increased reflectivity Z₄₅, Z₅₅, Z₆₅, and Z₇₅ synchronously reach the maximal values. The analysis of time distributions of the main radar parameters of hailstorms on a background of values of integral altitude is resulted. It is shown that local hailfall maximum intensities on the ground are observed after the achievement of maximum integral altitude with a certain delay. It enables to predict zones of the greatest hail damage in a mode of radar observation.     

Sausage MHD Waves in Incompressible Flux Tubes with Twisted Magnetic Fields

Twisted magnetic flux tubes are of considerable interest because of their natural occurrence from the Sun’s interior, throughout the solar atmosphere and interplanetary space up to a wide range of applicabilities to astrophysical plasmas. The aim of the present work is to obtain analytically a dispersion equation of linear wave propagation in twisted incompressible cylindrical magnetic waveguides and find appropriate solutions for surface, body and pseudobody sausage modes (i.e. m = 0) of a twisted magnetic flux tube embedded in an incompressible but also magnetically twisted plasma. Asymptotic solutions are derived in long- and short-wavelength approximations. General solutions of the dispersion equation for intermediate wavelengths are obtained numerically. We found, that in case of a constant, but non-zero azimuthal component of the equilibrium magnetic field outside the flux tube the index ν of Bessel functions in the dispersion relation is not integer any more in general. This gives rise to a rich mode-structure of degenerated magneto-acoustic waves in solar flux tubes. In a particular case of a uniform magnetic twist the total pressure is found to be constant across the boundary of the flux tube. Finally, the effect of magnetic twist on oscillation periods is estimated under solar atmospheric conditions. It was found that a magnetic twist will increase, in general, the periods of waves approximately by a few percent when compared to their untwisted counterparts.     

A new global ocean hydrographic climatology

This report describes the main features of the recently published World Ocean Experiment–Argo Global Hydrographic Climatology. This climatology is based on profile data from ships, Argo floats, and sensors attached to marine mammals. As an important deviation from the widely used climatologies produced previously by the National Oceanographic Data Center, the spatial interpolation was performed on local potential density surfaces, so that no ‘artificial water masses’ were created. In addition to monthly fields of temperature and salinity, gridded maps of the upper mixed layer depth are now provided.