57
Clouds
and Precipitation
A 2–3-fold increase of the probability of anomalously intense winter and
summer precipitation in Western Siberia conditioned by anomalous thermal cur‑
rents in the Arctic and Atlantic (i. e., in a positive phase of the Atlantic multi-dec‑
adal oscillation) has been revealed based on numerical experiments in [25].
The influence of the Siberian High on the characteristics of winter cloud
cover (cloud fraction and type) has been evaluated based on ground-based ob‑
servations on the Russian territory [17]. A long-term relation between cloud
cover and the Siberian High has been established. It is shown that a 1 hPa en‑
hancement of the Siberian High leads, on average, to one additional cloudless
day in the south of Siberia, which is primarily related with a decrease of strati‑
form clouds and rainclouds. A decrease in winter Siberian cloud cover during the
last years, which has also been noted in [7, 8], can be explained by the observed
enhancement of the Siberian High.
Based on a 25-year series of observations in different parts of Nizhniy
Novgorod and Kirov Regions, cases of freezing precipitation and various glaze-
and-rime phenomena hazardous to communication lines and transportation have
been investigated, as described in [26]. Based on the obtained data, some phys‑
ical-statistical traffic-climate models are proposed. These models are employed
by meteorologists for the needs of road maintenance services.
As a result of complex data analysis, a permanent presence of amor‑
phous-phase liquid water (referred to as ‘A-water’) in definitely ice-containing
clouds has been suggested in [27]. The author describes this water phase as
possessing physical properties largely different from those of common super‑
cooled water. Additionaly, it was concluded that in cold clouds, which are gen‑
erally thought of as purely liquid-water ones, a fine, and thus previously unde‑
tected ice fraction coexists with common supercooled water. The author believes
the new results and conclusions can radically change the conventional notion of
the optical, radiation, and other properties of ice‑containing clouds as a physical
disperse medium. As a consequence, conventional knowledge of liquid polymor‑
phous water should broaden, thus serving the needs of both cold cloud physics
and water physical chemistry.
1.2. Convection, convective cloud characteristics
and cloud water content
Atmospheric convection and convective fluxes resulting from ordered verti‑
cal air movement are processes associated with the whole class of hazardous
weather phenomena. Therefore, investigation of convective clouds as the main
visual indicator of convection is conventionally given much attention. Consid‑
ering the vastness of the Russian territory, which explains the local peculiarities
58
of convection processes, convection as a mesoscale phenomenon is usually stud‑
ied on a regional scale. The results obtained, which are reflective of the local
features of convection, are further used in modeling and predicting regional-scale
hazardous phenomena. They serve to develop special forecasts for all branches
of economy, but basically for aviation and transport in general, as well as for the
needs of an energy sector.
Regional studies of convection. Daily data on the formation of convective
clouds and phenomena of convective nature during the warm season of 2008
have been analyzed for the Far-East area. The relevant statistics is presented and
comparison with the climatic data performed. Typical synoptic situations accom‑
panied by hazardous convective weather phenomena are described [28]. Based
on radar data, over two hundred summer mesoscale convective systems (MCS)
have been investigated in central Russia, over an area with a 200-km radius
around Moscow, which have been classified by their morphology. The morphol‑
ogy of such systems is the basis for predicting weather hazards including lines
with heavy showers and squalls [29]. Three types of lines are distinguished: lines
with 100-km monolithic segments of over a 40 dBZ reflectivity; lines of inter‑
mittent convection — combinations of linear and node-like amorphous storms,
as well as convex and concave arched systems frequently forming families of
occlusion spirals. Nonlinear MCSs include circular radio echo structures similar
to open mesoscale cells, or small 30-km arcs. However, the most severe storms
occur along extended MCS development axes [29].
Climatic descriptions of Western Siberia convective resources are presented
[30]; the influence of local physiographic features on the convective potential of
the atmosphere of Western Siberia has been studied [31]. Convection character‑
istics on stormy days have been studied in Gorny Altai [32].
The characteristics of thunderstorm cells have been investigated based on
observations in Yakutia [33]. Using thunderstorm location network data, it has
been established that increasing thunderstorm activity (lightning density in the
region) results in a larger number of thunderstorm centers and thunderstorm
cells. It was concluded that the size and lifetime of thunderstorm cells in Yakutia
correspond to the data for North America and the European part of Russia. It was
shown that the larger the extension of thunderstorm cells, the higher is the light‑
ning intensity in the cells.
Statistical analysis based on hail hazard radar data, using automated identifi‑
cation of convective cells and estimation of their parameters, has been fulfilled
for Stavropol Territory and the Crimea [34]. Automatic data processing has
shown that >56% and 49% of hail convective cells in Stavropol area and the
Crimea, respectively, are soft-shower and small-hail ones causing no damage,
and 30% of convective cell reach mean intensity in both regions, with only 8%
in Stavropol area and 17% in the Crimea developing to cause severe hail damage.
N. A. Bezrukova, A. V. Chernokulsky