STATIONARITY,
TREND AND PERIODICITY OF PRECIPITATION AT THE ZAGREB-GRIČ OBSERVATORY FROM
1862 TO 1990
Marjana Gajić-Čapka
Abstract: This paper
deals with climatic change in the annual, warm half-year and cold half-year
precipitation data during the last 129 years, since the beginning of the series
in 1862 to 1990, at the Zagreb-Grič Observatory (j = 45°49', l = 15°59', H = 159 m a.s.l.) located
in the northwestern part of Croatia. The analysis has been deduced by using
tests for normality, the “quick test” for stationarity according to Schönwiese
and Malcher, weighted moving average filters, the Mann-Kendall rank statistic
for trend, and the power spectrum analysis.
The analysis
shows the stationarity of time series of precipitation amounts. A generally decreasing,
not statistically significant trend is present over the entire time interval
(1862-1990). The annual and warm half-year precipitation spectra can be fitted
by Markov “red noise” continuum and the cold half-year precipitation series by
that of “white noise”. Quasi-periodic oscillations appear in two spectra
ranges: short (2 – 6 years) and medium (16 – 43 years).
Key words:
precipitation, stationarity, trend, periodicity, power spectrum, Zagreb,
Croatia
EVALUATION
OF 1961-1990 STANDARD CLIMATOLOGICAL NORMALS
Josip Juras, Vjera Juras
Abstract: The comparison
of standard climatological normals for the periods 1931-1960 and 1961-90
indicates a certain increase in winter temperatures and a decrease in summer
temperatures in Croatia. In the monthly precipitation totals there is an
opposite trend. Weakening of the continental climate characteristics has
recently been accompanied by a decrease of interannual variability of mean
monthly temperatures. Temperature normals for the 1961-90 period approach more
closely the mean values for the entire period of observation in Zagreb than any
other standard normals. It is shown that the often advocated advantage of short
period (5 or 10 years) normals as a more reliable basis for future value
estimations, has no justification.
Key words:
climatological normals, climatic fluctuation, Zagreb, Croatia
AERIAL ANALYSIS
OF THE STRONGEST NORTH ADRIATIC ALPEX BORA CASE
Alica Bajić
Abstract: This paper
presents the results of an aerial analysis of the bora case on 6-7 March 1982
using aerological data from 10 stations in the region 40°-49° N, 10°-22° E. The
objective analysis method has been constructed for the presentation of the
isentropic surfaces and the two-dimensional isentropic divergence and the
vertical component of vorticity. The objective analysis scheme considered seems
to be capable of describing the main three-dimensional features of air flow
during bora: the descent of a stable bora layer not only along the NE bora
flow, but also perpendicular to this flow in the upstream region; the region of
vertical divergence forming a “dead region” with strong turbulence downstream;
the anticyclonic vorticity in the lee of the Alps and cyclonic circulation in
the mid-Adriatic before the bora onset.
Key words:
Adriatic bora, objective analysis, isentropes
SEVERE SNOWSTORM
15 – 18 MAY 1991 ASSOCIATED WITH A MESOSCALE CYCLONE DEVELOPMENT OVER THE
ADRIATIC
Vlasta Tutiš, Branka Ivančan-Picek and Vesna Jurčec
Abstract: The late
snowstorm in southwestern Croatia in May 1991 was associated with the Alpine
lee cyclogenesis. The synoptic analysis has confirmed the theoretical concept
of lee cyclogenesis which emphasise the role of an oreigenic cold air blocking
on the windward side of the Alps with a simultaneous displacement of the local
maximum of high level potential vorticity. However, it has been found that the
basic causes of a high precipitation amount and a very late snowstorm were
processes of a subsynoptic scale, not detected in the standard synoptic
analysis. We are trying to prove the association of severe storm with the fast
development of a mesoscale vortex over the Adriatic.
Key words:
cyclogenesis, snowstorm, Adriatic cyclones, potential vorticity
THE WORD OBORINA
AND ITS MEANING IN METEOROLOGY
Ivan Penzar, Branka Penzar
Abstract: The subject
of this paper is first appearance of the noun oborina in Croatia dictionaries
and since when the noun has been used as a meteorological term meaning
precipitation. It explains why this term and not some other derived from the
verb padati (to fall) has been accepted in meteorology. Definitions of the term
oborina by Croatian meteorologists and examples of similar definitions in some
other languages are quoted.
Key words:
precipitation – Croatian term for
Zdenko Franić
Abstract: Fallout 137Cs
in Zagreb has been investigated since 1965. An exponent decline in
radioactivity followed the nuclear moratorium. After the nuclear accident in
Chernobyl, high radioactivity levels were detected again. The residence time of
137Cs in fallout reflects the mechanism by which it was released
into the atmosphere (atmospheric nuclear weapon tests or the Chernobyl nuclear
accident). The spring peak of radioactivity in fallout can be explained by
meteorological phenomena. The deposition velocity of 137Cs for the
period 1986-1990 was calculated. 137Cs: 134Cs activity
ratios in fallout were discussed.
Key words: 137Cs,
fallout, mean residence time, deposition velocity
WEATHER PHENOMENA
DURING THE 13 – 31 JULY 1990 FOREST FIRE ON THE ISLAND OF HVAR
Marko Vučetić
Abstract: This paper
analyses the meteorological elements, which should be taken into consideration
in forest fire prevention. The forest fire on the island of Hvar, which lasted
intermittently from 13 do 31 July 1990 has been taken as an example to show
that the breaking out and development of fires greatly depend on the climatic
and weather factors of a particular location. Comprehensive and efficient
forest-fire prevention is not possible without interdisciplinary research, of
which meteorology is only a segment. However, practice has shown that even
existing knowledge and experience in this field are rarely being adequately
applied.
Key words:
forest fire
POTENTIAL BENEFIT
OF METEOROLOGICAL INFORMATION IN TRAFFIC
Živko Trošić
Abstract: In the
introduction the role and importance of meteorological services in the traffic
valorization of the Republic of Croatia is pointed out. The second chapter
gives the aims and lists the users of meteorological information in traffic, it
identifies and explains the nature of users' requests, the variety and content
of meteorological information, the users' relation towards this information,
and the potential benefit for traffic. The third chapter explains the necessity
of introduction the meteorologists with the activities of the users of
meteorological information and their qualifications with the purpose of
achieving optimal usage. In the fourth chapter the composition of a simulation
model for exploring and adapting the potential benefits of meteorological
information in traffic is given, with a short description of users, by applying
a cost/benefit analysis to a simple example.
Key words:
meteorological information, traffic, cost/benefit
THE ADRIATIC
BORA AND HYDRAULIC FLOW OVER THE MOUNTAIN
Višnja Vučetić
M. Sc. Theisis – Zagreb University, Faculty of Natural Sciences,
Zagreb, 1991, 130 pp.
Summary: The vertical
atmospheric structure was analysed in 6 situations with severe bora of Vsred ³ 17.0 m/s in the period 1959-1963 on the basis of radiosounding data in
Split. In addition to data from Zagreb, aerological data from Belgrade were
used for studying the bora layer. The measurements in Split made possible a
comparison of theoretical results, obtained by the application of the hydraulic
theory, and observations.
It is shown
that during severe bora on the mid-Adriatic, besides surface or elevated
inversions, one or two upper-level inversions were reflected in the upstream
region. These inversions separate the higher and lower atmospheric air flow and
make the lower fluid behave according to the hydraulic law. The data support
the same mechanism for severe bora generation and its continuance in
quasi-stationary situations on the northern and mid-Adriatic.
Severe bora on
the mid-Adriatic, where the broad and high Dinaric mountain range opposes the
upstream flow, is connected to a thick bora layer above Zagreb ((o = 2.8 km) within which a strong NE air flow occurs (5o = 12.1 m/s). The upper boundary of this layer splits
over the mountain (Split (1 = 1.8 km with 5 = 9.1 m/s) in agreement with the modelling assumption but it was also
found that this isentropic layer descends to the east toward Belgrade ((o = 2.3 km with 5o = 7.3 m/s) which can not be accepted in
two-dimensional models.
Thus, although
the application of the hydraulic theory with small variations of surface bora
intensity successfully estimated the maximum bora velocity and the downstream
bora layer height, analyses show that two-dimensional hydraulic theory could
not completely explain bora occurrence on the mid-Adriatic. This required a
study of a three-dimensional bora structure, which was carried out analysing
aerological data from Zagreb, Belgrade and Split.
It is shown
that the upstream structure of the lower troposphere over Belgrade does not
always indicate a NE flow perpendicular to the mountain range, as the usual
case is in the northern Adriatic (Zagreb).
An anticyclonic
relative vorticity field prevails in the bora layer along the steeply sloping
isentropic level toward the Adriatic, appears over the western part of
Yugoslavia and convergence fieldover its eastern part. This is obviously a sign
of a three-dimensional upstream structure in the mid-Adriatic bora flow.
Consequently,
this analysis emphasizes, the special and temporal variations of wind field and
stability during bora occurrence not only along the NE bora flow, but also
perpendicular to this flow in the upstream area. This study, therefore,
concludes that a complete picture of the bora structure and consequently its dynamics
can only be achieved by applying three-dimensional models and the corresponding
wind and temperature fields.
Smiljan Visković
M.Sc. Thesis – Zagreb University, Faculty of Natural Sciences,
Zagreb, 1992, 106 pp
Summery: The causes of
severe bora in Split were studied on the sample of 15 cases. Selected from the
period January 1980 – January 1983, in which the mean hourly speed was bigger
or equal to 17.2 m/s. The macro, meso and local scale processes, as well as
their mutual interactions, were studied.
On macro
scales, it was found that the bora is connected with a cold air outbreak from
the north. During severe bora on the coast, high gradients of pressure appear,
caused by the anticyclone to the north-west and the cyclone to the south-east
of the bora area.
On meso-scales,
from radiosounding data in Zagreb, in all cases, a cold air outbreak from the
north and a low level jet (LLJ) were noticed. The mesoanalysis of three ALPEX
bora cases of which two were of the frontal and one was of the postfrontal
type, were presented showing a connection between LLJ and the strengthening and
weakening of the bora in Split. In almost all selected cases the bora was
stronger on the Mid-than on the Northern Adriatic, but at the same time there
were a great variations in the strength of the bora depending on the influence
of the locality.
In all selected
cases the bora on the Observatory Split-Marjan was stronger and lasted longer
than on the station of Resnik. This fact calls for a more detailed study of the
influence of local components and the channel effects in relation to the
hydraulic, catabatic and other possible mechanisms of the bora on the
Mid-Adriatic.
Control to the
Northern Adriatic situations, the application of Smith's 2D hydraulic theory
was not valid in the majority of selected cases. That fact imposes the need for
the introduction of a 3D atmospheric model, in which the air can go around the
mountain or, in a very stable stratification, the air flow can go through the
mountain valleys.
Parallel
observations of soundings in Zagreb and Belgrade showed that during bora on the
Adriatic Sea, a NW air flow sometimes appeared above Belgrade. That NW flow
causes the divergence and lowering of the streamlines and a stagnation on the
windward side which can prevent the occurrence of stronger bora on the
Mid-Adriatic, causing a channelling effect. The divergence and lowering of the
air are in agreement with recent investigations of the 3D effects on the wind
flow around or above mountain.
The qualitative
analysis leads to the conclusion that the bora is presumably caused by the
interaction of macro, meso and local scale processes and that in some case one
of those components can prevail. However, a quantitative analysis and study of
the causes of bora can give positive results only through numerical simulation
by mesomodel for a limited area with variable lateral and time boundaries which
would reflect the influence of macroscale processes on the intensity and
duration of bora at a certain locality.