[Data sources and services][Weather phenomena and forecasting]
Topography and the local environment
Molodezhnaya station (opened in February 1962) is located on the southern shore of Alasheyev Bay with coordinates of 67040’ S and 45050’ E and a height above sea level of 42 m. The settlement is located in a small coastal oasis Thala Hills in 0.5-0.6 km from the shore. The station area presents a hillocky locality with rocky ridges separated by snow-covered depressions and lakes. The Cosmonauts Sea in the station area is ice covered much of the year. There are many icebergs. The landfast ice width by the end of winter reaches almost 100 km. The rise to the ice Antarctic dome begins in 1.5-2.0 km from the shore. An outlet Kheis glacier is located in 15 km eastward from the station and the outlet Campbell glacier at the same distance southwestward.
The settlement numbers more than 70 structures - living and office buildings, a mess-room, upper-air sounding station, aerological building, power station, radio-center and warehousing. West of the settlement there is a runway for aircraft and in 12 km to the east-south-east of the station a snow-ice airfield was constructed for heavy aircraft. At present the Molodezhnaya station was temporarily decommissioned.
Data sources and services provided
The amount of information received in the form of synoptic messages. Shiopborne and drifting buoy data allowed compilation of the weather maps as well as pressure topography maps AT-500 for 00 and 12 GMT. If necessary, the maps for 06 and 18 GMT were also prepared. The archive of synoptic maps and satellite images for all operation years is stored in St. Petersburg at the AARI. These maps provide a possibility to review the atmospheric processes near the Earth’s surface and in the tropospheric layer in East Antarctica, as well as in the Weddell Sea and in the east of the Bellingshausen Sea. In previous years, radio communication could be interrupted completely during geomagnetic perturbations in the upper atmospheric layers (magnetic storms) that were mainly observed in winter. About one-two cases of interrupted radio communication due to this reason were usually observed every month from May to October. In these cases a synoptic had to analyze the atmospheric processes using only meteorological satellite data received on a daily basis at Molodezhnaya. Note that satellite data are the most timely and reliable type of information in the Antarctic.
Instead of the absent synoptic messages from the oceanic regions of the Southern Hemisphere aero-synoptic data of the European Center for Medium-Range Weather Forecasting. This information included a surface and altitudinal (AT-500) analysis, as well as the pressure field forecasts for 24 and 72 hours. A synoptic analysis of the …. In the GRID code was used for processing the synoptic maps for the Southern Hemisphere while the prognostic information was invaluable for issuing low and medium-range weather forecasts.
The surface analysis maps for 00 GMT from the Australian RMC in Kanberra were received via facsimile communication on a regular basis.
In addition, a synoptic map covering directly the Australian continent and the adjoining oceanic area was received. A surface analysis from the South African RMC in Pretoria for 06.00 GMT on the southern areas of the Indian and the Atlantic Oceans was received by facsimile on a daily basis.
Based on all aero-meteorological and satellite data received, the weather Bureau prepared and disseminated the following information among the users:
daily synoptic surface and altitudinal charts for 00 GMT, nephanalysis charts and “Meteostat” cables based on satellite data, semi-diurnal and daily weather forecasts for the regions of the Russian Antarctic stations and sea areas, three-day weather forecasts on requests of ships and stations, weekly and monthly reviews of synoptic processes and weather conditions for the regions of the Antarctic, large-scale ice charts on applications of ships, 10-day, monthly reviews of ice conditions for the Antarctic Seas, ice consultations on requests, atmospheric circulation forms in the Southern Hemisphere and types of synoptic processes on a monthly basis.
The main goals addressed by weather forecasters at Molodezhnaya was hydrometeorological information support of activities of different scientific teams, sledge-tractor traverses, aircraft flights, navigation of ships and loading-unloading at the stations also during helicopter operations.
At present, due to decommissioning of the Molodezhnaya station, preparation is underway for organizing a new Weather Bureau at the Progress Base (Prydz Bay) based on new technologies for synoptic data acquisition and processing.
Important weather phenomena and forecasting techniques
a) General overview
The main factor determining weather processes of the Molodezhnaya area is the cyclonic activity with cyclones passing along both zonal and meridional trajectories. During the cold half a year the number of days with moving cyclonic eddies in the Cosmonauts Sea reaches 24 a month, on average. More than half of this number is comprised by the cyclones with zonal trajectories moving along the Antarctic front. The remaining group of cyclones (8-10 cases a month, on average,) is related to the meridional processes.
The zonal processes are characterized in all cases by a steady western transport in the troposphere and lower stratosphere and hence by a rapid movement of surface cyclones and anticyclones from west to east. At the meridional processes, surface pressure features move with the significant northerly and southerly components, resulting in the interlatitudinal air mass exchange in different coastal zones of the Cosmonauts Sea.
Typically, this air exchange occurs as a result of merging of the Antarctic High ridges in the troposphere with the Highs of the subtropical belt. Near the Earth’s surface, this relation is expressed in the form of the blocking ridge. The locations of this ridge and of the Low motion trajectories determine the weather character in the coastal regions connected with different types of the meridional process.
The influence of different meridional circulation forms governed by the development of warm West Atlantic and East Atlantic ridges, on the weather in Molodezhnaya is significant. In the first case, the cyclonic activity in the Falkland branch is strongly developed. However, at Molodezhnaya the weather is mainly governed by the influence of the eastern branch of the West Atlantic ridge and is distinguished by certain stability. In the second case, the … branch of Low motion is developed. The exits of warm and humid cyclones with intense storm activity along this trajectory also determine unstable weather in Molodezhnaya with alternating strong easterly and southeasterly (catabatic) winds with snowfalls and blizzards and significant air temperature oscillations in the wintertime.
At the zonal type of processes, shallow occluded cyclones with small moisture content move at the Antarctic front. They rarely approach the coast and frequently stable weather is established at Molodezhnaya without snowfalls and wind increase.
During the warm half of the year, the frequency of the exit to the coast and activity of cyclonic eddies significantly decreases with the corresponding increase of stability of weather conditions. However, the extreme conditions are sometimes also formed in the summer and their forecasting is connected with certain problems. The corresponding example will be given below. It has to be noted that forecasts based on a global model in the Cosmonauts Sea and north of it in the absence of significant orographic obstacles yield quite satisfactory results in respect of the development of large-scale cyclones and blocking ridges not only for 1-2 days, but also for a large period. These forecasts are obviously taken into account by weather forecasters serving sometimes as the only basis in forecasting. On the other hand, the mesoscale systems are identified in this region with difficulty and only from cloud images. In general, the study of these comparatively rare features that obviously result sometimes in significant weather deterioration is still at the beginning.
b) Surface wind and the pressure field
Easterly and south-easterly winds prevail at Molodezhnaya of 8 wind directions. Compared to the historical averages the easterly winds prevail in the summer months and the south-easterly winds are most frequent in the other months of the year. During the period March to July their frequency of occurrence comprises around 50% with increasing south direction (the third by the frequency of occurrence) up to 18-20%. On average during a year the share of the aforementioned directions comprises 85% of all observations at the synoptic times. The main factor here is the surface pressure distribution. The zone of easterly transfers covers the coastal regions of the Cosmonauts Sea up to latitude 650, as follows from the analysis of moderate pressure charts. In the winter months, the climatic trough axis is located slightly more to the south and in the summer months slightly north of the indicated latitude.
Thus the main wind types for the coastal Antarctic regions (cyclonic, catabatic and transient) have quite a steady direction in Molodezhnaya, but the wind speeds sharply change and over a wide range. Especially intense and persistent cyclonic winds are observed at the exiting … cyclones to the coast that were formed in the warm and moist oceanic air. They are accompanied with thaws and heavy snowfalls. The catabatic wind following the cyclonic wind has a hurricane force rising enormous masses of freshly fallen snow in the air.
The catabatic (gravitation) wind occurs above the steep slope of the dome whose height in Molodezhnaya at a distance of 350 km reaches 2500 m. The conditions for regular gusty winds in the nighttime with a speed from 0 to 25-30 m/s are created already at the beginning of autumn. At this time, the ocean produces a warming effect and the cold catabatic flow penetrates far to the sea. In winter in connection with air cooling in the coastal area above the sea ice the catabatic wind becomes irregular. Sometimes it decreases only at the dome foot and calm weather persists at the station. Continuous catabatic wind at the station is observed in the presence of relatively warm air masses near the coast.
The development of the catabatic wind at the station is related to the cyclonic activity near the coast. The largest wind speeds are observed in the rear part of the cyclones when the catabatic and cyclonic wind vectors coincide. Strong catabatic winds are formed above Molodezhnaya with appearance of strong jet southerly currents in the troposphere above the dome. These currents form strong lower level flows that merge with the surface catabatic flow at the northwestern slope of the ice sheet ridge, which is directed from the center of East Antarctic towards the Enderby Land. The surface relief features distribute separate jets depending on the slope forms and exposition. Note that appearance of snow eddies above the Vechernyaya mountain in the outlet Hays Glacier area is one of the direct signs of the beginning of sinking at Molodezhnaya. If typically the direction of the sinking flow at Molodezhnaya is 1400, it comprises 1600 at the airfield near the Vechernyaya Mountain.
The sinking flow becomes especially gusty at the end of winter. Its strong jets can interact with the relief irregularities contributing to the occurrence of eddies. The southeasterly wind speed reaches 40 and even 50 m/s at an almost complete loss of visibility. In summer, the catabatic wind can also be significant (with individual gusts up to 25-30 m/s) but this is rare and typically occurs in the nighttime (between 1-5 a.m.). The diurnal heating of the dome slope induces a pressure decrease and air advection from the sea towards the dome. Only with the passage of an easterly-south-easterly jet current in the troposphere, the catabatic wind can also persist in the daytime but is less intense.
The number of days with the storm winds in Molodezhnaya reaches 221 a year and with the snow storm –174. The largest average speed for a multiyear period falls on May comprising 14.5 m/s. The largest maximum speeds are close or equal 40 m/s from April to October the maximum gust being observed in May –54 m/s.
The presence of wind data from permanent stations, ships, buoys and automated weather stations at the synoptic charts is a necessary condition for the analysis of the surface pressure field and 850 hPa field. It is also important to take into account the influence of the topography of the area, as they do not necessarily reflect the general character of the air mass transfer in the given area. This should also be taken into account in updating the model pressure forecasts that should be used with caution south of 700.
c) Clouds and precipitation
The amount of total cloud, on average, for a year in the Molodezhnaya area is 6.9 points. The months with elevated cloud amount are April and March when average cloud amount is 7.7 points. The largest frequency of occurrence of sky overcast (8-10) reaching 72% is observed during the same period. This indicator does not decrease significantly in the same months of the year. In other words, gloomy weather is predominant for Molodezhnaya. However, the frequency of occurrence of clear sky in the multiyear plan is observed in 20 to 30% of observations at standard times in all months of the year, except for March and April. Active cyclonic activity in the Antarctic coast zone is a cause of constantly significant cloud cover. The upper and low clouds typically prevail of the cloud forms. However, at the exit of deep cyclones from the side of the sea, the multilayered systems accompany the passage of the main and secondary frontal divides, including low stratus and cumulus clouds with precipitation in the form of snow.
In accordance with the features of the development of cyclonic activity, the maximum precipitation is observed at Molodezhnaya in autumn, in March and April. He secondary maximum is observed at the end of winter and at the beginning of spring, and namely, in August and September. The minimum precipitation is notable falling on the summer months – December and January. Typically, less than 350 mm of precipitation falls out in the solid form except for rare cases in the summer months. Note that the precipitation sums are determined at the Russian Antarctic stations with some errors, as during a blizzard with the snow fallout from clouds part of snow blown from the snow surface is collected in the precipitation gauge.
One usually pays attention to the similar physical-geographical conditions and atmospheric circulation conditions of Mirny and Molodezhnaya. This similarity is manifested in the characteristics of clouds and precipitation. In addition, both stations similar to the entire coast of East Antarctica is characterized by significant air dryness and comparatively low relative humidity values by months and for a year. The yearly average comprises 65% for Molodezhnaya and 71% for Mirny. For the ice-covered coastal areas, the low humidity values are connected with air drying at discharges. The annual humidity variations as well as water vapor elasticity at Molodezhnaya is very weakly pronounced.
The forecast of cloud flowing over and precipitation depends typically on the correct forecasting of the development of synoptic situation provided aerosynptical and satellite data are available.
d) Visibility – blizzards, fog and whiteout
Good visibility conditions prevail at Molodezhnaya under the conditions of general air transparency typical of Antarctica. The frequency of occurrence of visibility greater than 10 km comprises 85-88% of all observation times in the summer months notably decreasing in winter. Blizzards are the main factor restricting visibility, hence to predict deteriorating visibility means to correctly predict the wind increase accompanied with snow fallout. Blizzards occur in the presence of non-compact snow cover and the wind speeds greater than 7-9 m/s. Since strong winds in Antarctica predominate, the number of days with blizzards is more than 170 days a year. In winter, it comprises 18-22 days a month and in summer it typically does not exceed 1-2 days.
Stationing of cyclone is the most dangerous synoptic situation connected with occurrence of strong blizzards when the station is affected by its rear part and storm winds can persist for a long time. Drifting snow is obviously a less dangerous phenomenon than blizzards, but they are quite frequent in the winter conditions. In summer, their frequency of occurrence notably decreases as the non-compact snow cover is quite seldom observed at this time of the year.
Advective sea fogs at Molodezhnaya are very rare occurring during low wind weather. These are purely local phenomena of short duration. Frosty fog is even a rarer phenomenon compared to sea fog in summer.
After a strong blizzard, a fine snow dust remains in the air at the station and especially in the vicinity of the station at the dome slope at low wind. This snow dust remains in the suspended state for many hours and may result in the snow haze phenomenon with visibility reducing to 4 km. A successful forecast of such a phenomenon for an experienced forecaster is quite possible.
The whiteout, an optical phenomenon that is known in polar countries, presents a significant danger for aviation flights under the Antarctic conditions. At sunny weather, discontinuous and not dense stratus clouds and uniform snow surface, there is no contrast and the horizon becomes not discernible. An example of a dangerous synoptic situation is a period when a subtropical high pressure ridge in the Cosmonauts Sea area merges with the Polar High ridge. This leads to the formation of a jet southerly current at the eastern periphery of the high pressure isthmus typically at the tropopause height. A zone of continuous mainly stratocumulus cloud is formed at the dome at the contact of warm and cold air masses. At some time the southeasterly winds can increase and the horizontal visibility reduce under the snowfall conditions. Orientation in space above the dome is very difficult under these conditions since the horizon blends with the snow surface. Then when the wind decreases, and visibility improves and the Sun is at a sufficient height, a no less dangerous situation can appear – the whiteout. There is a rule, according to which the flights above the dome especially inland are better to undertake with the cloud-free forecast.
e) Air temperature
Formation of the temperature regime in the Molodezhnaya area, similar to the other Antarctic areas is influenced by solar radiation, the underlying surface character and atmospheric circulation. According to the “Atlas of the Antarctic”, this region belongs to the coastal climatic zone in the form of a narrow coastal strip including outlet glaciers, landfast ice, oases and areas with snow-free hills and rocks.
The albedo value at Molodezhnaya is quite significant, but much less than in Mirny. From the middle of spring and up to the beginning of autumn, the value of absorbed radiation flux and the full balance in bare areas become much greater compared to the surrounding snow surface. The annual balance unlike Mirny is positive. It is positive here for around 7 months and 4 months at Mirny. A comparatively large radiation heat flux to the underlying surface in summer is compensated by the heat loss to air warming. The summer at Molodezhnaya is warmer and the winter is colder than in Mirny, but the air temperature multiyear averages at both stations are negative in all months.
The maximum monthly temperature average is in January (-0.40) with the absolute maximum of +9.00. August is the most severe month (-18.80) at the absolute minimum of –42.00. Air temperature variations from day-to-day are related to the atmospheric process features, primarily to the exits of cyclones from the northern oceanic regions to the coast. The pattern of development of such processes is sometimes quite complicated being connected with the study of large-scale circulation modification over extensive Antarctic areas and in the zone of temperate latitudes. For example, such phenomenon as the formation of significant air temperature increases (several degrees higher than the mutiyear norm) at Molodezhnaya in summer can be connected with the variant of the process beginning 1-2 weeks ahead in the Australian sector at the development of the meridional Ma circulation form. According to this variant a sharp large-scale warming in the tropospheric layer begins with the formation of a strong blocking ridge and the surface High south of Tasmania. A steady southward warm air transport is established at the ridge southern periphery with cyclones developing at the West-Australian branch. This contributes to intensified coastal High and its displacement south-westward to the near-pole area resulting in a sharp air temperature increase along its pathway, for example up to above zero values at Vostok station.
Then changing its direction the High moves towards the Cosmonauts Sea. A significant air temperature increase at Molodezhnaya and at Syowa occurs with increasing southeasterly flows. Warm air flowing from the High downward the ice dome slopes from a height of more than 3000 m warms additionally as a result of the foehn effect and an almost daily incoming solar radiation. At some standard times, the air temperature in coastal oases can rise to 8-120 C.
The forecasters at Molodezhnaya developed in this way many variants of typical processes leading to the anomalous weather conditions in different seasons.
In weather forecasting for the coastal Antarctic regions, it is necessary to constantly make observations of turbulence occurring both at a height in the jet current zone and near the surface especially at the ice slopes. Typically, a westerly and southwesterly jet current occurs above the region of the Low exiting from temperate latitudes along the meridional trajectory 12-18 hours beforehand. Strong heat advection from the north in the frontal cyclone part leads to the development of continuous low clouds, snowfalls and precipitation in the form of drizzle. Under such conditions clouds and warm air extends to the dome over 400-500 km where the most strong turbulence is observed at the contact with cold air, which is often accompanied with icing of aircraft.
During the sinking flow in winter the largest eddy formation occurs when a mass of very cooled air forms near the coast above the landfast ice while the catabatic wind mixed with the upper layer air has a higher temperature. In these cases strong jets of such flow incorporate in the surface layer of cold air and interact with it. The irregular relief contributes to eddy formation. Occasionally, tornado-like eddies with a 10-150 m diameter are observed with the wind speeds of 50 m.
The winter and spring flow is sometimes manifested in occurrence of eddy waves with a horizontal axis descending from the ice slopes. In the rear part of the eddy a strong downward flow is felt while in the frontal wave there a sudden deterioration of visibility due to rising snow dust.
The effect of the aforementioned and similar phenomena on the landing aircraft can be very dangerous. There is large gap of full-scale observations of turbulence and a need in projects investigating these phenomena using modern instruments and equipment, as well as experience of investigating the dynamic and thermodynamic processes in the boundary atmospheric layer obtained, for example, during the International winter expedition to the Weddell Sea in 1989.
Aurora view on the station (photo from the archive) Àéñáåðãè íà ðåéäå ñòàíöèè (ôîòî èç àðõèâà) Tractors near the station (photo from archive) Tractors as a vehicle (photo from archive) Pinguins in the vicinity of the station (photo from archive) Launch of meteorological rocket (photo from the archive) View of the station #1 (photo from the archive) View of the station #2 (photo from the archive) View of the station #3 (photo from the archive)