AN EXCESSIVELY FROSTY MONTH - JANUARY 1963

Transcription

1 AN EXCESSIVELY FROSTY MONTH - JANUARY 1963 ELENA NICULESCU 1 Key-words: January 1963, negative thermal imblances, Romania Against the continental-temperate climatic background of Romania, the presence of very frosty winters, and of very low temperatures are a rarity. They represent limit major negative deviations associated with notable negative thermal imbalances of all the air temperature variables and constitute unique episodes over a long period of time. Negative thermal imbalances, that is temperature falls far below the multiannual means, and biting frosts are generated by massive arctic or continental polar air advections in conjunction with radiative cooling induced by the presence of a snow-layer and the dominance of strong anticyclonic activity. One such month was January 1963, competing with January 1942 which is considered to be the coldest 20 th - century month. In order to outline the physiognomy of the 1963 month, a detailed study was undertaken of the average and minimum annual and monthly temperatures in terms of the multiannual means ( ) registered at all the meteorological stations (over 150) operational at that date. Deviations were computed and referred to the 1942 month. The mean temperature of the year 1963 was often found to drop below the multiannual mean. More than 80% of the stationary values were lower than the multiannual means. Negative deviations vary between -0.1 and -1.6ºC, usually as low as -0.5ºC in almost all the regions of Romania (fig.1). Deviations lower than 0.5ºC occurred in the central sector of the West Plain, in the south of the Romanian Plain and on the Moldavian Plateau. Fig annual mean temperature deviations from the multiannual mean ( ) Positive deviations were characteristic of the high mountain peaks: Omu, Vladeasa and Cuntu (+ 0.4ºC), which rise above the cold mass of air that covered nearly the whole country. A heat island (positive deviations) is found in the Bend Curvature area sheltered from the cold air currents and benefiting by the foehn effects. Similarly, on the Black Sea coast, the body of water playing a moderating role. 1 Institute of Geography, Romanian Academy

2 Elena Niculescu The mean temperature in January 1963 is more relevant for the intensity of the cooling process, when negative monthly mean temperature deviations were registered at all the meteorological stations operational at that time. Temperatures were found to stand by ºC below the multiannual mean (fig.2). The cooling process was particularly intense in the east of Romania, where temperatures dropped at -13ºC (Rădăuţi); milder values were recorded in the high mountain area, with deviations above -5ºC (Omu -3.8ºC, Ţarcu - 4.3ºC and Vlădeasa -4.7ºC peaks). But for a few exceptions, it was strong temperature inversion that covered the whole territory and unleashed that process. Fig. 2 January 1963 mean monthly deviations from the multiannual January mean In the West Plain and Hills, January 1963 values were of 7-9ºC (compared to a multiannual mean of 5-6ºC); in Banat -6ºC (compared to -5ºC); under 8-9ºC in the Romanian Plain and in the Danube Valley (compared to 5-7ºC); -5-7ºC in Dobrogea and in the Danube Delta (compared to 5-6ºC). The 1963 value equalled or surpassed the 1942 one by only ºC in January. In both cases it was the same areas that registered the highest deviation (under -8º and -9ºC, respectively), namely in the southwestern Romanian Plain and the eastern extremity of the Moldavian Plateau (fig.3). Fig. 3 January 1942 mean temperature deviation from the January multiannual mean The minimum temperature in January 1963 is a most relevant indicator of the intensity of cooling that month, with frequent values of -30ºC (at some 30% of the stations) and even lower (-35ºC at 2.1% of the stations). That situation is pretty similar to the January 1942 one, with the only difference that the frequency of < 35ºC temperatures is higher in 1963 (by 4 to 1). 206

3 An excessively frosty month January 1963 In both years -25º -29.9ºC were the rule (fig.4). The differences seen between the two months are also due to the different number of stations (55 as against 150). Fig. 4 Frequency (%) of absolute minimum temperature deviations in 1942 (A) and January 1963 (B) Noteworthy, the minimum temperatures recorded at many stations in January 1963 represent absolute values for the whole series of their data. As a result, it is a unique month in regard of the frequency of absolute minimum temperatures. Some 30% of the stations operating in January 1963 registered minimum temperatures by 0.1º-0.5ºC lower than in January At Craiova station for example, the lowest 1942 January value was -30.5ºC, dropping at -35.5ºC in 1963, which is the lowest record of the station. Over 31% of the country's weather stations have the lowest temperature value of January 1963 registered so far (fig.5). Figure 5 shows absolute January 1963 minima (under -35.0ºC) in the West Plain (Timişoara -35.3ºC), the Transylvanian Depression (Dej -35.2ºC), the intramountainous depressions of the Eastern Carpathians (Joseni -38.0ºC), with values close to the January 1942 all-country record (Bod -38.5ºC), and the Oltenia Plain (Craiova -35.5ºC). Minima of -30ºC and -35ºC occurred in the east of the country, by 1º-5ºC lower than in 1942 (Bacău -30.8ºC versus -27.6ºC; Iaşi -30.6ºC versus -23.3ºC; Botoşani -30.3ºC versus -25.5ºC). Milder absolute decreases had the east of the Romanian Plain (-22º -27ºC), the Bend Subcarpathians (-20ºC), Dobrogea (-19º -21ºC) and the Black Sea coast (-16º -17ºC). The mountain area minimum in January 1963 slided little under -30ºC (Omu -30.5ºC and Vladeasa -30.0ºC peaks) most of the high altitude stations registering a minimum above this value (Lăcăuţ -28.7ºC, Rarău -28.0ºC, Ţarcu -27.8ºC, Cuntu -25.4ºC, Parâng -24.2ºC, Ceahlău Munte -24.1ºC, etc.), very relevant of the thermal inversion. The impact of that massive cooling process is reflected also by the other thermal variables specific to the cold season e.g. frosty nights (min. temperature < -10ºC), freeze days (min. temperature < 0ºC) and winter days (max. temperatures <0ºC). 207

4 Elena Niculescu Fog. 5 Absolute minimum temperatures The incidence of frosty nights is 15-25, the fewest (under 15 cases) occurring in the southwest of Romania where Mediterranean influences maintain a moderate climate. Even so, at Berzasca and Moldova Veche they recorded 12 and 14 such nights, respectively. In the southern sector of the coastal area (Mangalia) there were fifteen, the highest incidence of frosty nights (23-25) having the northeastern part of Romania (Roman, Iaşi, Cotnari, Avrămeni, Dorohoi, Rădăuţi and Suceava - 25 cases). 208

5 An excessively frosty month January 1963 Freeze days occurred almost throughout January 1963, with top frequency (21-30 cases) being registered at most weather stations. Winter days, in their turn, are a frequent presence (22-31 cases). The origin of the January 1963 massive coolings - one of the tough negative thermal imbalances of the 20 th century, is rooted in the particularities of the air circulation in the highest strata of the atmosphere. The January 1963 pressure distribution in Europe shows a belt of increased atmospheric pressure over the northern half of the Continent favoured by the advection of a wave of cold polar air that induced a particularly severe frosty weather. Of the many waves of frost (12), it was the interval that recorded most of the absolute minimum temperatures (fig.6). Fig. 6 Synoptic situations between January 18-25, 1963 The process of cooling was enhanced by the thickness of the snow layer that covered the whole country: cm in the West Plain and Hills; cm in the Romanian Plain; cm in the Getic Subcarpathians; cm in the Subcarpathians and the Moldavian Plateau. The snow blanket was the deepest in the second and the third decades of the month and it corresponds to the lowest temperature record. Summing up, we would say that January 1963 ranks among the severest negative thermal imbalances of the 20 th century. Many of that month's temperatures represent unique absolute values of that century and are expected to remain so over the next decades of the 21th century, too. 209

6 Elena Niculescu BIBLIOGRAPHY Bogdan Octavia, Niculescu Elena (1992), Phénomènes climatiques extrêmes pendant le dernier siècle en Roumanie, R.R.G., 36, p Bogdan Octavia (1998), Fréquence des refroidissements et des réchauffements massifs pendant le dernier siècle en Roumanie, R.R.G., 42, p Bogdan Octavia (1999), The incidence of massive cooling and heating in the west of Romania during the 20 th century, Proceedings of the Regional Conference of Geography, Timişoara-Novisad-Szeged-Tübingen, Edit. Mirton, Timişoara, p Bogdan Octavia, Niculescu Elena (1999), Riscurile climatice din România, Academia Română, Institutul de Geografie, Compania Sega-International, 280 p. Ciulache S. (2000), Temperaturile minime absolute pe teritoriul României, Com. de Geografie, Fac. de Geografie, Univ. Buc., p Niculescu Elena (1993), Răciri şi încălziri masive în ultimul secol în România, S.C.G., XL, p *** (1966), Anuarul meteorologic pe anul 1963, C.S.A., Institutul de Meteorologie, Bucureşti 210