Köppen Climate Types in Observed and Simulated Climates

The Köppen climate classification was applied to the observed gridded climatological sets and the outputs of four general circulation models (GCMs) over the continents of the Earth. All data had been acquired via the Data Distribution Centre established by the Intergovernmental Panel on Climate Change. The ability of the GCMs to simulate the Köppen climate zones identified in the real data was explored and possible future (global warming) changes in the climate types' distribution for each GCM were assessed. Differences in the area distributions derived from the GCMs' recent climate simulations give evidence about uncertainties generally involved in climate models. As to the global warming simulations, all GCM projections of warming climate (horizon 2050) show that the zones representing tropical rain climates and dry climates become larger, and the zones identified with boreal forest and snow climates together with the polar climates are smaller.     

On the Integrability of Limited-Area Numerical Weather Prediction Model ALADIN over Extended Time Periods

This note summarizes results of the first integration of regional numerical weather prediction model ALADIN in a climate mode. The ALADIN model, developed in an international cooperation led by Météo France, is operationally used for weather prediction. The grid step of the model is 12 km; the integration domain covers a major part of Europe. A one-month-long run has been performed with this model on observed boundary conditions (represented by assimilations by the global model ARPEGE). It is demonstrated that no excessive error is generated and accumulated in the model during the integration; hence the model is integrable for extended time periods and may serve a basis for a development towards a regional climate model.     

Diurnal Variation of Gravity Wave Activity at Midlatitudes in the Ionospheric F Region

We investigate the short-term fluctuations in the period range from 15 to 180 minutes in the electron density variations of the F region ionosphere. Electron density profiles obtained at the ionospheric stations of Pruhonice (49.9° N, 14.5° E) and Ebro (40.8° N, 0.5° E) at five minute time sampling have been used for this analysis. The diurnal changes of the activity of the acoustic gravity wave fluctuations (AGW) show a clear enhancement during and several hours after sunrise. The periods of such AGW's are about 60 to 75 minutes and these waves propagates vertically through the ionosphere from a source located at an altitude of 180-220 km. The most likely source for these events seems to be passage of the Solar terminator.     

A methodology to estimate renewal time scales in estuaries: the Tagus Estuary case

High-resolution hydrodynamic models are a common tool to simulate water dynamics in estuaries. Results from these models are, however, difficult to interpret without the aid of additional parameters to integrate the information. In this paper a methodology to understand the transport patterns in the Tagus Estuary is proposed. It is based on the computation of two renewal time scales: residence time and integrated water fraction. This last parameter is used to build a dependency matrix that gives the integrated influence of each region of the estuary at a selected point. The parameters are computed using a Lagrangian transport model coupled to the hydrodynamic model. Results show that Tagus Estuary has two different types of regions: the central part of the estuary, with low renewal efficiency, and three regions with higher renewal efficiency. Renewal mechanisms are, however, different for each region as shown by the dependency matrix. Comparison of renewal time scales with results from a water-quality model revealed that residence time is not a limiting parameter for primary production in the Tagus Estuary.Responsible Editor: Hans Burchard     

Book Review: Monitoring the Comprehensive Nuclear-Test-Ban Treaty: Regional Wave Propagation and Crustal Structure. By Howard J. Patton and Brian J. Mitchell (Eds.), Birkhäuser Verlag, 2001, 222 pp., softcover,Euro 45, ISBN 3-7643-6550-1

Studia Geophysica et Geodaetica -     

Seismic Activity Around and Under Krakatau Volcano,Sunda Arc: Constraints to the Source Region of Island Arc Volcanics

There is general agreement that calc-alkaline volcanic rocks at convergent plate margins are genetically related to the process of subduction (Ringwood, 1974; Maaloe and Petersen, 1981; Hawkesworth et al., 1997). However, opinions on the mode and site of generation of primary magma for island arc volcanism differ substantially. The site of generation of calc-alkaline magma is thought to be either in the mantle wedge (Plank and Langmuir, 1988; McCulloch and Gamble, 1991) or in the subducting slab (White and Dupré, 1986; Defant and Drummond, 1990; Edwards et al., 1993; Ryan and Langmuir, 1993). We present seismological evidence in favour of the latter concept. A distinctive seismicity pattern around and under the Krakatau volcano was identified during systematic studies of the SE Asian convergent plate margins by means of global seismological data. A column-like cluster of events, probably associated with the dynamics of the volcano, is clearly separated from the events in the Wadati-Benioff zone. The accuracy of hypocentral determinations of the events of the cluster does not differ from the accuracy of the events belonging to the subducting slab. The depths of the cluster events vary from very shallow to about 100 km without any apparent discontinuity. On the other hand, there is a pronounced aseismic gap in the Wadati-Benioff zone directly beneath the volcano at depths between 100-150 km. The Krakatau cluster connects this aseismic gap to the volcano at the surface. The pervasive occurrence of earthquakes in the continental wedge between the subducting slab and the Earth surface bears witness to the brittle character of the continental lithosphere and casts doubt on the existence of large-scale melting of mantle material. The aseismic gap (Hanu and Vank, 1985), interpreted by us as a partially melted domain occurring in subducted slabs in practically all active subduction zones that reach depths greater than 100 km, is here used as evidence for the location of the primary source region of island arc volcanics in the subducting plate.     

Simultaneous SOHO and Ground-Based Observations of a Large Eruptive Prominence and Coronal Mass Ejection

Coronal mass ejections (CMEs) are frequently associated with erupting prominences near the solar surface. A spectacular eruption of the southern polar crown prominence was observed on 2 June 1998, accompanied by a CME that was well-observed by the LASCO coronagraphs on SOHO. The prominence was observed in its quiescent state and was followed throughout its eruption by the SOHO EIT and later by LASCO as the bright, twisted core of the CME. Ground-based H observations of the prominence were obtained at the Ondejov Observatory in the Czech Republic. A great deal of fine structure was observed within the prominence as it erupted. The prominence motion was found to rotate about its axis as it moved outward. The CME contained a helical structure that is consistent with the ejection of a magnetic flux rope from the Sun. Similar structures have been observed by LASCO in many other CMEs. The relationship of the flux rope to other structures in the CME is often not clear. In this event, the prominence clearly lies near the trailing edge of the structure identified as a flux rope. This structure can be observed from the onset of the CME in the low corona all the way out to the edge of the LASCO field of view. The initiation and evolution of the CME are modeled using a fully self-consistent, 3D axisymmetric, MHD code.     

Radio Emission from Three-dimensional Relativistic Hydrodynamic Jets: Observational Evidence of Jet Stratification

High-resolution, high signal-to-noise ratio, blue-violet spectra of three red giant branch tip stars in M15 have been obtained with the Keck I High-Resolution Echelle Spectrograph. These spectra have been analyzed to determine the abundances of several neutron-capture elements, including the radioactive chronometer element thorium. There are two principal results of this study. First, the abundances of the heavier (Z>/=56) elements for each of the three stars is well matched by a scaled solar system r-process abundance distribution. Second, a weighted mean-observed Th/Eu ratio for the stars implies an age for the neutron-capture material in M15 stars of 14+/-3 Gyr, in reasonable agreement with other recent age estimates for Galactic globular clusters.     

Solar rotation in the subphotospheric layers

The solar rotation rate at latitudes 0°, 15° and 30° has been inferred by averaging the results of 120 regions of 15°×15°, which have been studied over a total area of about 75° in latitude and 360° in longitude. A local helioseismology technique, the ring diagram analysis method, has been used to analyse the horizontal velocity vectors from about 0.95 R up to the surface. Our results are in very good agreement with those of other authors over most of the depth range. However, near the surface we find sharp local features which are not reported in other studies. The independent measurements of the rotation rate in the north and south hemispheres show asymmetries below 0.975 R . The data used are full-disc dopplergrams taken by Solar Oscillation Investigation/Michelson Doppler Imager (SOI/MDI) on board of the SOlar and Heliospheric Observatory (SOHO) during its first Dynamic Program, between 1996 May and June.     

Formation Of Coronal Mhd Shock Waves – I. The Basic Mechanism

The formation and evolution of a large amplitude MHD perturbation propagating perpendicular to the magnetic field in a perfectly conducting low plasma is studied. The perturbation is generated by an abrupt expansion of the source region. Explicit expressions for the time and the distance needed for the transformation of the perturbation's leading edge into a shock wave are derived. The results are applied to coronal conditions and the dynamic spectra of the radio emission excited by the shock are synthesized, reproducing metric and kilometric type II bursts. The features corresponding to the metric type II burst precursor and the moving type IV burst in the case of kilometric type II bursts are identified. A specific radio signature that is sometimes observed at the onset of a metric type II burst is found to appear immediately before the shock wave formation due to the associated growth of the magnetic field gradient. Time delays and starting frequencies of bursts' onsets are calculated and presented as a function of the impulsiveness of the source-region expansion, using different values of the ambient Alfvén velocity and various time profiles of the expansion velocity. The results are confronted with the observations of metric and kilometric type II solar radio bursts.