Understanding of Freezing Precipitation Processes and their Changes - PowerPoint PPT Presentation

Understanding of Freezing Precipitation Processes and their Changes Pavel Groisman 1,4,7 , Xungang Yin 2 , Olga Bulygina 3 , Irina Danilovich (Partasenok) 5 , and Olga Zolina 6,4 (1) North Carolina State University Scholar at NOAA National Centers for Environmental Information, Asheville, North Carolina, United States (pasha.groisman@noaa.gov} (2) ERT, Inc., at NOAA National Centers for Environmental Information, Asheville, North Carolina, USA (3) All-Russian Research Institute of Hydrometeorological Information - World Data Centre, Obninsk, Russia (4) P.P. Shirshov Institute for Oceanology, Russian Academy of Sciences, Moscow, Russia (5) Center of Hydrometeorology and Control of Radioactive Contamination and Environmental Monitoring, Minsk, Belarus (6) Le Laboratoire de Glaciologie et Géophysique de l’Environnement, Grenoble, France (7) Hydrology Science and Services Corporation, Asheville, North Carolina, USA.

Objective (GEWEX Cross-Cut project) : To improve our understanding of future changes in hazardous cold/shoulder season precipitation and storms, especially occurring near 0°C. These extremes can be devastating and are subject to changing climate.

Long-term synoptic stations used in our analyses; 1- and 3-hourly data for the past 40 years First group are station data First group collected for Groisman et al. 2016. The second group includes the station data that we are currently using to cover the entire extratropics. The third group will include the upper air data for further studies of the freezing events phenomena. Second group Europe, 550 stations Belarus Kyrgyzstan

Temperatures near 0°C in the extratropics

Next four slides show the occurrence of the “near 0°C weather conditions” in the extratropics – This occurrence is quite frequent over the entire northern extratropics, e.g., • over Russia, from the Arctic Islands to the Caucasus Mountains, • over Europe, and • over North America, from Alaska to Carolinas and – In the past 45 years, its temporal changes (decrease) are observed only in the southernmost areas of Russia and the United States and over the entire Europe from Mediterranean to Northern Norway .

Percent of surface air temperature observations within the [-2°C, 2°C] interval over latitudinal zones of North America 25 West of 95°W East of 95°W % 20 15 10 5 0 Lat. °N 70-75 65-70 60-65 55-60 50-55 45-50 40-45 35-40 30-35 25-30 In East Canada for this analysis, we did not have long-term stations data in latitudinal zones 65°-70°N and 50°-55°N

Percent of the surface air temperature observations within the [-2°C, 2°C] interval over latitudinal zones of Russia 25 % ETR west of 60°W ATR east of 60°E 20 15 10 5 0 70-75 65-70 60-65 55-60 50-55 45-50 40-45 Lat.°N ETR – European territory of the Russian Federation

Percent of the surface air temperature observations within the [-2°C, 2°C] interval over latitudinal zones of Europe 29 25 % 20 15 10 5 0 75-80 70-75 65-70 60-65 55-60 50-55 45-50 40-45 35-40 30-35 Lat. °N

Percent of observations over Northern Europe with the surface air temperature within the [-2°C, 2°C] interval 20,0 % Zone 55°-60°N Zone 50°-55°N 17,0 14,0 11,0 8,0 dObs/dt = -5.5%/40yrs; R² = 0.43 dObs/dt = -4.4%/40yrs; R² = 0.35 5,0 29,5 % Zone 65°-70°N Zone 60°-65°N 26,5 dObs/dt = -4.0%/40yrs; R² = 0.29 dObs/dt = -3.1%/40yrs; R² = 0.21 23,5 20,5 17,5 14,5 1970 1980 1990 2000 2010 1970 1980 1990 2000 2010 2020 Over the entire Europe, we observe temporal changes (decreases)

CHARACTERIZATION OF FREEZING EVENTS USING OTHER METEOROLOGICAL VARIABLES

Freezing precipitation distribution (%) by associated surface air temperature, T a (over entire Russia) 30 30 % 25 25 20 20 15 15 10 10 5 5 0 0 -20,5 -17,5 -14,5 -11,5 -8,5 -5,5 -2,5 0,5 3,5 6,5 9,5 -20,5 -18,0 -15,5 -13,0 -10,5 -8,0 -5,5 -3,0 -0,5 2,0 4,5 7,0 9,5 Freezing rain by T a Freezing drizzle by T a

Fraction of freezing rain events for different near surface relative humidity ranges over the Russia 60 Relative Humidity, % 50 Fraction, % 40 30 20 10 0 RH range ≤ 70 71-80 81-90 91-95 96-100

Upper air normalized temperature anomalies at 700 hPa for freezing events at five US Stations Three CONUS stations Two Alaskan stations • Three CONUS stations • Two Alaskan stations 3,0 2,0 1,0 0,0 1.24.1975 1.24.1978 1.24.1981 1.24.1984 1.24.1987 1.24.1990 1.24.1993 1.24.1996 1.24.1999 1.24.2002 1.24.2005 1.24.2008 1.24.2011 1.24.2014 1.25.1975 1.25.1978 1.25.1981 1.25.1984 1.25.1987 1.25.1990 1.25.1993 1.25.1996 1.25.1999 1.25.2002 1.25.2005 1.25.2008 1.25.2011 1.25.2014 -1,0 -2,0 Anomalies are expressed in fractions of standard deviations of “normalized” daily temperature values at 12 UTC. Seasonal cycle variability of mean daily values and variances are eliminated by normalizing. CONUS = Contiguous U.S.

Air temperatures differences between the days with freezing events and the “nearby” days (1975-2014) °C Vertical temperature differences during the days with freezing events (850 hPa – surface; 700 hPa – 850 hPa; 500 hPa – 850 hPa). inversions

Air temperatures differences between the days with freezing events and the “nearby” days (1975-2014) °C Vertical temperature differences during the days with freezing events (850 hPa – surface; 700 hPa – 850 hPa; 500 hPa – 700 hPa). Inversions.

Initial Initial free eezing ing pr prec ecipit ipitatio tion n ch charact cterizations • 60% of freezing rain and 55% of freezing drizzle events occur while surface air temperatures, T a , are within [-1.5°C, 0.0°C] and [-2.0°C, -0.5°C] intervals respectively. • 85% of freezing rain events occur when near surface relative humidity, RH, exceeds 90% . • Only 7% of meteorological observations were made when RH values exceed 90% and simultaneously T a remain within the [-1.5°C, 0.0°C] interval. Over the entire Russian Federation, 80% of all freezing rain events are reported under these near- surface weather conditions. • Using combined synoptic and upper air data during freezing events over the Contiguous U.S. and Alaska, we noticed that most of freezing events occur with warmer than usual lower troposphere (e.g., during warm fronts). On average, the T 700 hPa anomalies are at ΔT 700,normalized = + 1°C ( p = 0.16 ).

HOMOGENEITY OF THE FREEZING EVENTS REPORTING

Inhomogeneity issues due to automation 4.0 Top. Average number of days with freezing drizzle reported 3.0 2.0 by the U.S. and Canadian 1.0 stations. 0.0 Bottom . Average number of 4.0 days with freezing drizzle 3.0 (blue dots) and freezing rain 2.0 (red dots) for the United 1.0 States only. 0.0 1975 1980 1985 1990 1995 2000 2005 2010 2015 … and reporting 4.0 Days per year Region-wide mean changes in the 3.0 frequency of moderate and heavy freezing 2.0 rain events (days year -1 ) that followed the 1.0 introduction of METAR reporting formats in August 1996 over Northeastern U.S. (east 0.0 1975 1980 1985 1990 1995 2000 2005 2010 2015 of 80°W and north of 40°N).

Insufficient temporal coverage by 3-h. reports Annual number of hours with gololed when at least one freezing event was observed during the year sorted by R , ratio of the number of these hours to the number of 3-h. reports of freezing events over 444 Russian stations for the 1977-2011 period => true annual number of freezing events, NFE: NFE reported × 3/max(R,0.5) (if NFE reported ≠ 0) NFE = 0 (otherwise) 2000 Hours per year We have to “scale-up” 1500 the event numbers based upon 3-h reports everywhere 1000 when 3-h reports are used: Russia, 500 Kyrgyzstan, most of Fennoscandia and 0 Baltic States. 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

CLIMATOLOGY

Climatology of freezing events over North America for the 1975-1994 period Days Days Annual freezing rain frequency Annual freezing drizzle frequency

Climatology of freezing events over Russia and Norway Annual frequency of freezing rain days The same, but for freezing drizzle days

Climatology of all freezing events over Russia and Belarus Annual frequency, days

Climatology of freezing rain events over Europe

CHANGES IN THE LAST DECADE

Possible cause: The Arctic temperature increase/Annual surface air temperature anomalies area-averaged over the 60°N - 90°N latitudinal zone Lugina et al. 2006, updated

Recent changes in the freezing precipitation frequency Climate conditions in the last decade have been very different from the past decades. For example, each year the Arctic (60 ° - 90 ° N) surface air temperature was warmer than any year during the period of instrumental observations. Therefore, we conducted change assessment in the freezing precipitation characteristics by comparing them in the last decade (2005-2014) with those for the previous three decades (1975-2004). We show these changes in day yr -1 for freezing rain, freezing events (Northern Eurasia), freezing drizzle (for Russia only), and separately for occurrences of intense freezing rain and drizzle over Russia. Thereafter, we present a Table with regional climatologies and the estimates of the last decade change for selected climatic regions of Russia, Europe, and North America.