Conditions for freezing precipitation at some airports of Russia and the CIS: IV. Airport of Nizhni Novgorod

Abstract

Results of study of conditions for freezing precipitation (FP) at the airport of Nizhni Novgorod based on 20-year series of surface observations are described. The cloud tops are estimated from radiosonde data. It is found that the monthly mean FP frequency does not exceed 0.44%; the phenomenon occurs from October to February. Over 20 years, a total of 113 FP episodes were observed, or less than six episodes annually. Freezing precipitation is more frequent at night and in the morning and very rare in the afternoon, at surface air temperatures not exceeding 0 o C and not below -10 o C; in half of the cases, the air temperature is within -0.1 to -2.0 o C. Surface wind is most frequently from south or southwest, while in the lower 4-km layer, according to the radiosonde data, wind direction mostly veers with height from south to west and north. In the boundary layer, FP is often associated with low-level jet streams, most frequently of southwest direction in the cloudy layers. The warm layers within and below the clouds occur in more than 20% of the cases. The most typical precipitation is FP from "all cold" clouds. Using objective criteria of the fronts, synoptic situations, advection, and baroclinicity, it is shown that almost all cases of freezing rain are observed in frontal zones, while freezing drizzle is as frequent at the fronts as under airmass conditions. Both types of FP are associated mainly with high baroclinicity and warm advection. The results can be used to develop an objective method of FP forecasting. 431FP occurrence frequency as dependent on (a) temperature of the cloud base and top and (b) surface air temperature and maximum temperature in the cloudy layer. (1) Freezing rain; (2) freezing drizzle.

Freezing precipitation in Russia and the Ukraine

“…The classical mechanism suggests that the -16 -14 -12 -10 -8 -6 -4 -2 snow and ice particles, which precipitate from the cold upper part of the cloud, m layer (inside or below the cloud) and then, in a form of droplets, fall into the lowe become supercooled droplets and finally freeze up at the surface. threshold values are not reached, statistical criteria are applied (Chakina et al, 2003(Chakina et al, , 2005a. The soundings associated with FP are classified with respect to warm layer positions (Table 3).…”

Simulation of the variations of the temperature of droplets in freezing precipitation

“…Freezing pre cip i ta tion is ob served in win ter and tran si tion sea sons at mid dle and high lat i tudes as well as in moun tain ar eas at lower latitudes; it re sults in neg a tive con se quences for pop u la tion, power engineering, motor, rail way, and air trans port [2][3][4][10][11][12][13][14]. In [14], the idea is con sid ered of the cli mate char ac ter is tics and mech a nisms of freez ing pre cip i ta tion as well as the meth ods of its fore cast ing.…”

“…The au thors of the pres ent pa per used the nu mer i cal so lu tion of the equa tion of heat con duc tiv ity in the drop let and ice crust by the fi nite dif fer ence method tak ing ac count of the fol low ing con di tions: the phase tran si tion on the mov ing wa ter-ice in ter face; the cur va ture of phase tran si tion bound ary; vari a tions of heat ex change con ditions on the bound ary be tween the ice coat ing and sur round ing at mo sphere due to the ver ti cal vari a tions of air tem per a ture by means of form ing the strat i fi ca tion type with the warm layer in the cloud (a "warm nose") sit u ated over the con sid er ably cooled un der ly ing sur face [10,14]. Such sim u la tion of drop let temper a ture for real syn op tic con di tions was car ried out for the first time.…”