1.
Leder, N., A. Smirčić and I. Vilibić (1998): Extreme
values of surface wave heights in the northern Adriatic. Geofizika,
15, 1-13.
ABSTRACT:
Extreme
return values of significant wave heights were calculated using the data of
wave heights measured in the open part of the northern Adriatic (platforms
PANON and LABIN, lighthouse Sv. Ivan na pučini), by approximating the
distribution of monthly extremes by Fisher-Tippet curve (F-T I). Parameters of
F-T I distribution of extremes were estimated using three methods: graphic
method, method of moments, and maximum likelihood method. Comparison of the
results obtained from each method has shown that extreme return values of
significant wave heights obtained using the maximum likelihood method best
agree with the data of direct instrumental measurements. The greatest
significant wave heights are to be expected in the winter period, from December
to February. Absolute calculated monthly maximum of a significant wave height
occurs in February, being 7.54 m for the return period of 100 years. Major
deviations are evident in the summer period (overestimated values), due to a
small number of measured data and their dispersion. Extreme expected value of
significant wave height in the northern Adriatic for the return period of 100
years is 8.57 m, from which a maximum wave height of about 14 m is estimated,
being considered real as regards the maximum measured value of 10.8 m.
Keywords: Wind generated surface waves, theory of extremes,
northern
[PDF]
2.
Herceg, I. (1998): The energy cycle in a cyclone over the Bay of Genoa. Geofizika,
15, 15-25.
ABSTRACT:
Zonal
available potential energy, eddy available potential energy, eddy kinetic energy
and conversion of zonal to eddy potential energy have been evaluated for the
period from 5 to 15 February 1986 using data from Wetterbericht charts. These
terms were calculated for a limited domain ranging from 400N to 500N latitude
and from 50E to 200E longitude. A cyclone developed over the Bay of Genoa
during the considered period. The system formed simultaneously at all levels in
the troposphere as was noticeable on the synoptic charts. The cyclone life
cycle could be described by time variations of the eddy available potential
energy, since it increased during the intensifying and decreased during the
weakening stage of the system. A stability diagram has been used to examine
connection of the cyclone amplification and calculated energy terms with
conditions in the atmosphere presented by critical meridional temperature
gradient. The results obtained by the stability diagram correspond to energy
estimations. In those days for which the stability diagram indicated
amplification of the cyclone, the eddy energy terms increased and so the
cyclone growth was evident on the synoptic charts.
Keywords: Available potential energy, kinetic energy, energy
transformation, eddy, cyclone, stability diagram
[PDF]
3.
Telišman Prtenjak, M., A. Marki and P.
Benard
(1998): Refinement of the vertical diffusion
scheme in ARPEGE/ALADIN model. Geofizika, 15, 27-51.
ABSTRACT:
In
atmospheric numerical weather prediction (NWP) models, the use of long
time-steps as allowed by efficient numerical/dynamical schemes can lead to
spurious oscillations due to the parameterized physical part. Typical examples
of this are the oscillations associated with simplified parameterization
schemes for vertical diffusion or shallow-convection, such as usually used for
NWP. The oscillations generated by K-type vertical-diffusion schemes are well
documented, and being called fibrillations; they are characterized by high
temporal and vertical frequencies. Since they are linked to high vertical
resolution, these spurious oscillations are generally found in the low-levels
of model's domain. In ARPEGE, the MÉTÉO-FRANCE NWP global model, and in ALADIN,
its limited-area model (LAM) version developed in cooperation with Eastern
European countries, and also used for operational NWP purpose, some
oscillations still remained in the evolution of the forecast fields, despite
the fact that a first anti-fibrillation scheme (AFS) had been included. This
study was made to examine the possible sources of these oscillations, through
the 1-D (vertical) version of these models. First, the parameterization of
shallow-convection (which is in fact part of the vertical diffusion scheme) was
found to be an important source of oscillations, and some solutions for
eliminating this problem are proposed. Second, the original AFS is shown not to
completely prevent the generation of fibrillations, and a more efficient
formulation is derived. All AFSs basically consist in a temporal first-order
decentering of the diffusion equation, keeping an explicit form for the
exchange coefficient itself. The AFS correction thus always improves the
stability at the expense of the accuracy in some way. In the new AFS proposed
here, the number of grid-points which need a correction is lessen from almost
90% to some 5%, resulting in a more accurate scheme. Unlike AFSs proposed in
the literature, the correction has now to be applied not only for grid points
of atmospheric stable conditions (i.e. Richardson number, Ri > 0) but also
for atmospheric slightly unstable conditions (Ri < 0).
Keywords: NWP model, ARPEGE/ALADIN model, shallow-convection,
Richardson number, fibrillation, anti-fibrillation scheme
[PDF]
4.
Lisac, I. and A. Marki
(1998): The auroral events observed from
Croatia and a part of surrounding countries. Geofizika,
15, 53-68.
ABSTRACT:
Descriptions
of 37 auroral (or polar light) events were analyzed that were published mostly
since the middle of the 18th century up to present days and observed within
latitudes from 42° to 45.5°N and longitudes 13° to 19°E (mainly on the
territory of Republic of Croatia). The list of auroral events includes date,
place and source of information and, for the most cases, visually observed
parameters such as: color, shape, distribution on the sky and time duration of
the phenomenon. Basic statistical results allowed the conclusions about the
most frequent occurrence of a particular parameter. The auroral events
correlate highly with the solar activity and in mentioned latitudes they
correlate also with the secular period of sunspots.
Keywords: Aurora, auroral calendar, aurora and sunspots, polar
light events
[PDF]
5.
Lyskova, E. L., T. B.
Yanovskaya and S.J. Duda (1998): Spectral characteristics of earthquakes along
plate boundaries. Geofizika, 15,
69-81.
ABSTRACT:
Earthquakes are investigated with epicentres located along
divergent and along convergent plate boundaries. Two criteria are applied in
order to distinguish between earthquakes featuring
anomalous “long-periodic” and “short-periodic”
radiation of body-waves: 1) deviation of the corner period Tc of the P-waves from the regression between Tc and the moment magnitude Mw;
and 2) the values of stress drop Ds.
It is found that earthquakes along divergent boundaries
radiate the seismic energy mainly at longer periods, and, vice versa, that such
along convergent boundaries radiate energy mainly at shorter periods. The
average stress drop for the former earthquakes is
estimated thereby to be 33 bars and for latter – 89 bars.
In a regional scale, for earthquakes in the Japan-Kuril area it is found
that the corner periods for strike-slip events are larger than those for thrust
events. The results confirm the findings of investigations based on the creepex
distribution along divergent and convergent boundaries, as well as the
findings related to the dependence of creepex on the source mechanism.
Keywords: Seismic moment, corner period, principle of
self-similarity, stress drop, focal mechanism
[PDF]
6.
Markušić, S., D. Herak, I. Ivančić, I. Sović, M. Herak and E. Prelogović (1998): Seismicity of
Croatia in the period 1993-1996 and the Ston-Slano earthquake of 1996. Geofizika,
15, 83-101.
ABSTRACT:
Seismic activity in Croatia and
surrounding areas in the 1993-1996 period was mostly confined to the previously
identified seismically active areas. Nine events (excluding aftershocks) with
the magnitude equal to or exceeding 4.5 occurred during that time. The most
important earthquake sequence is the one that started on September 5, 1996
(Ml=6.0, Imax=VIII MSK) in the Ston-Slano area (greater Dubrovnik region).
Microseismic locations of hypocentres of thousands of aftershocks, as well as
the best double-couple CMT solution for the main-shock indicate that the
earthquakes occurred on the NW-SE striking reverse fault system dipping towards
NE.
Keywords: Seismicity, Croatia, Ston-Slano earthquake
[PDF]
7.
Tiwari, R. K. and K. N. N. Rao (1998):
Correlated variations and periodicity of global CO2, biological mass
extinctions and extra-terrestrial bolide impacts over the past 250 million
years and possible geodynamical implications. Geofizika, 15, 103-117.
ABSTRACT:
Earth’s
history has been witness to recurrently alternating phases of catastrophic
evolution and dominant tectonic deformations, contractions and extension of
rifting and spreading leading to quasi-cyclic changes in sedimentary environment
and various earth processes. Recent studies have shown quasi-periodicities of
32 ± 2
Million years (Myr) in various endogenic (geomagnetic reversals, magmatic
events, mantle convection, various tectonic activities, climate change and
biological extinctions) and exogenic (impact cratering) processes indicating a
remarkable kinship. We present here time series analysis of the available CO2 record over the past 250 Myr decoded from
CaCO3 accumulation rates in sedimentary environment. The time series
analysis reveals an intriguing evidence of a dominant periodicity of 33 ± 2 Myr which
matches closely with a common “catastrophic periodicity” of 32 Myr
identified in various terrestrial and extra-terrestrial records. We argue here
for a common physical link among the periodic global CO2
variations, mantle convection, geomagnetic reversals, volcanism, geotectonic
cycles and enhanced cometary showers. We also suggest periodic variations in CO2
as one of the possible terrestrial stimulators for the oscillating
“greenhouse effect” and related climatic deterioration that result
in quasi-periodic mass extinctions. Identical “catastrophic cycles”
of endogenic and exogenic origin enhance the credence of their physical
linkages and uphold the “concept of non-uniformitarianism” in earth’s
processes.
Keywords: Periodicity, global CO2, geodynamics
[PDF]