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

Understanding of Freezing Precipitation Processes and their Changes

Pavel Groisman1,4,7, Xungang Yin2, Olga Bulygina3, Irina Danilovich (Partasenok)5, and Olga Zolina6,4

(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 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.

First group

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.

In East Canada for this analysis, we did not have long-term stations data in latitudinal zones 65°-70°N and 50°-55°N

%

5 10 15 20 25

70-75 65-70 60-65 55-60 50-55 45-50 40-45 35-40 30-35 25-30 West of 95°W East of 95°W

Percent of surface air temperature observations within the [-2°C, 2°C] interval over latitudinal zones of North America

• Lat. °N

ETR – European territory of the Russian Federation

5 10 15 20 25 70-75 65-70 60-65 55-60 50-55 45-50 40-45 ETR west of 60°W ATR east of 60°E Lat.°N

Percent of the surface air temperature observations within the [-2°C, 2°C] interval over latitudinal zones of Russia

%

Percent of the surface air temperature observations within the [-2°C, 2°C] interval over latitudinal zones of Europe

%

5 10 15 20 25 75-80 70-75 65-70 60-65 55-60 50-55 45-50 40-45 35-40 30-35

29

• Lat. °N

Percent of observations over Northern Europe with the surface air temperature within the [-2°C, 2°C] interval

Over the entire Europe, we observe temporal changes (decreases)

dObs/dt = -5.5%/40yrs; R² = 0.43 Zone 55°-60°N

%

dObs/dt = -4.0%/40yrs; R² = 0.29

14,5 17,5 20,5 23,5 26,5 29,5

1970 1980 1990 2000 2010

Zone 60°-65°N dObs/dt = -3.1%/40yrs; R² = 0.21

1970 1980 1990 2000 2010 2020

Zone 65°-70°N

dObs/dt = -4.4%/40yrs; R² = 0.35 5,0 8,0 11,0 14,0 17,0 20,0

Zone 50°-55°N

%

CHARACTERIZATION OF FREEZING EVENTS USING OTHER METEOROLOGICAL VARIABLES

Freezing precipitation distribution (%) by associated surface air temperature, Ta (over entire Russia)

Freezing rain by Ta Freezing drizzle by Ta

5 10 15 20 25 30

• 20,5
• 17,5
• 14,5
• 11,5
• 8,5
• 5,5
• 2,5

0,5 3,5 6,5 9,5

5 10 15 20 25 30

• 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

%

10 20 30 40 50 60 ≤ 70 71-80 81-90 91-95 96-100

Fraction, %

RH range

Relative Humidity, %

Fraction of freezing rain events for different near surface relative humidity ranges over the Russia

Upper air normalized temperature anomalies at 700 hPa for freezing events at five US Stations

• Three CONUS stations
• Two Alaskan stations
• 2,0
• 1,0

0,0 1,0 2,0 3,0

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

Three CONUS stations

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

Two Alaskan stations

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) Vertical temperature differences during the days with freezing events (850 hPa – surface; 700 hPa – 850 hPa; 500 hPa – 850 hPa). inversions

°C

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

°C

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, Ta, 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 Ta 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 T700 hPa anomalies are at ΔT700,normalized = + 1°C (p = 0.16).

HOMOGENEITY OF THE FREEZING EVENTS REPORTING

Inhomogeneity issues due to automation

• Top. Average number of days

with freezing drizzle reported by the U.S. and Canadian stations.

• Bottom. Average number of

days with freezing drizzle (blue dots) and freezing rain (red dots) for the United States only.

0.0 1.0 2.0 3.0 4.0 0.0 1.0 2.0 3.0 4.0 1975 1980 1985 1990 1995 2000 2005 2010 2015

0.0 1.0 2.0 3.0 4.0

1975 1980 1985 1990 1995 2000 2005 2010 2015

Days per year

Region-wide mean changes in the frequency of moderate and heavy freezing rain events (days year-1) that followed the introduction of METAR reporting formats in August 1996 over Northeastern U.S. (east

• f 80°W and north of 40°N).

… and reporting

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:

500 1000 1500 2000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5

Hours per year

NFEreported × 3/max(R,0.5) (if NFEreported ≠ 0)

NFE =

0 (otherwise)

We have to “scale-up” the event numbers based upon 3-h reports everywhere when 3-h reports are used: Russia, Kyrgyzstan, most of Fennoscandia and Baltic States.

CLIMATOLOGY

Climatology of freezing events over North America for the 1975-1994 period

Annual freezing rain frequency Annual freezing drizzle frequency

Days Days

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

days Annual frequency,

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.

Changes of the mean annual numbers of days with freezing rain between 2005-2014 and 2075-2004 periods

Changes of the mean annual number of freezing rain days between 2005-2014 and 1975-2004 periods

• ver

Europe

Changes of the mean annual numbers of days with freezing precipitation between 2005-2014 and 1975-2004 periods

• Freezing rain days
• Freezing drizzle days

Annual Freezing Drizzle Frequency area-averaged over Russia

Light and intense freezing drizzle event frequency arithmetically averaged over the long-term stations of the Russian federation. Light freezing drizzle occurrence (LFD) is approximately 10 times larger than this occurrence for intense freezing drizzle (IFD).

Changes of the mean annual numbers of days with all freezing events between 2005-2015 and 1977-2004 periods

Changes in the annual number of freezing precipitation-hours over Belarus between 2004- 2015 and 1977-2003 periods

• 40

40 80 120

23,4 24,5 25,4 26,0 26,4 26,9 27,5 27,9 28,3 28,8 29,2 29,6 30,1 30,3 31,0

Station changes sorted by longitude

Lon.,°E 10 20 30 40 23-26 26-29 29-32 Percent, changes Number of stations

• Lon. Range

Average change within longitude ranges °E

% %,

count

Annual freezing rain frequency, FRF, area-averaged over

North America, zone 50°- 60°N NE of East-European Plain North America north of 66.7°N Norway north of 66.7°N

Annual freezing rain frequency, FRF, area- averaged over Northern Europe days (year)-1

dFRF/dt=0.26 days/(10yr)-1; R² = 0.15 0,0 1,0 2,0 3,0 4,0 5,0

1975 1980 1985 1990 1995 2000 2005 2010 2015

Greenland and Iceland

dFRF/dt = 0.19 days/(10yr)-1; R² = 0.11 0,0 1,0 2,0 3,0 4,0 5,0

1975 1980 1985 1990 1995 2000 2005 2010 2015

Baltic Sea Region without Russia

Annual freezing rain frequency, FRF, area- averaged over the Steppe Zone of European Russia and the southern West Siberia

• Note the order of magnitude scale difference between the continental

Siberian region and the Steppe Region of European Russia

Freezing events at different elevation below 1 km from 1 to 2 km above 2 km Climatology, days(yr)-1 0.98 0.61 0.25 Changes between two periods, days(yr)-1

• 0.31
• 0.16

0.50

Annual frequency of all freezing precipitation events (freezing rain, freezing drizzle, and ice rain)

• ver Kyrgyzstan during the 1966-1990 period and

recent changes in this frequency during the 21st century

Data of 26 synoptic stations. For the 2009-2011, the data were not available for analysis

Long-term regional mean values of freezing rain frequency northern Europe and selected regions of North America and Russia for 1975-2014 and differences between the mean values for the last decade (2005-2014) and the previous 30-yr-long period (1975-2004) Region Regional mean values days yr-1 Diff. days yr-1

Significant changes by following tests

North America north of 66.7°N

1.8 1.06 t- & L- tests

North America, between 50°N and 60°N

2.5 0.28 L- & Rs- tests

Norway south of 66.7°N

1.1 1.05 all three tests

Norway north of 66.7°N

1.1 1.10 all three tests

Russian Atlantic Arctic

1.4

• 0.20

L- & Rs- tests

Northwest of the Great East European Plain

1.3 0.28 none

Northeast of the Great East European Plain

2.2 0.77 L- & Rs- tests

Greenland and Iceland

1.1 0.49

L- & Rs- tests

Baltic Sea Basin

2.0 0.60

all three tests

Statistically significant changes at the 0.05 level are in bold and at the 0.10 level are in bold italic.

Results in a nutshell

• Using synoptic data for the past 40 years, we

estimated the climatology of the frequency of freezing rain and drizzle occurrence for North America, Europe, Russia, and Kyrgyzstan and their changes in the past decade

• During the last decade, substantial changes in the

annual freezing rain occurrence were found:

– On the southern edge of our study domain (southeastern U.S., Central Europe, southern Russia) the frequencies of freezing events decreased along with the duration of the cold season; – In the Arctic (North America, Europe, and North Atlantic north of 60°N), in some taiga areas of Russia, and at high elevations (The Tian Shan Mountains), the frequencies of freezing events increased “following” the expansion of the short warm season.

• Changes in the occurrence of freezing drizzle were

estimated only for Russia. We found a statistically significant nationwide decrease in this element.

• 3. Increase in the number of days with Wangengheim-Girs circulation type W. This

circulation type is associated with unobstructed water vapor transport from Atlantic towards Europe

• 4. Expansion of the short warm season

.

• 1. Large-scale meandering.

Figure 2b from Francis and Vavrus, 2012, GRL, 39, L06801. Schematic of ridge elongation (dashed vs. solid) in upper-level heights caused by enhanced warming in Arctic relative to mid-latitudes. Higher amplitude waves progress eastward more slowly, as indicated by arrows

Possible causes of increases of freezing events in the Arctic

• 2. Northward shift in Eurasian storm tracks (warm corner of cyclones can be more

frequently found over the cold surfaces)

Percent distribution of freezing rain events over Russia by associated surface air temperature Ta during the 1976-2004 and post 2004 periods

• Practically no differences with time in freezing rain distribution by Ta
• 10
• 5

5 10 15 20 25 30

• 6,5 -6,0 -5,5 -5,0 -4,5 -4,0 -3,5 -3,0 -2,5 -2,0 -1,5 -1,0 -0,5 0,0 0,5 1,0 1,5

1975-2004 after 2004 Differences

Ta %

That’s it!

Results in a nutshell

• Freezing precipitation events frequency and intensity are

changing in contemporary climatic changes, and these changes are not yet well understood and/or documented

• Automation (where it was introduced) and temporal paucity

(e.g., 3-h. versus 1-h. reports) affect the homogeneity of reporting of freezing events (especially, for freezing drizzle and intense freezing events)

• Using synoptic data for the past 40 years, we estimated the

climatology of the frequency of freezing rain and drizzle

• ccurrence for North America, Europe, Russia, and Kyrgyzstan

and their changes in the past decade

• During the last decade, substantial changes in the annual

freezing rain occurrence were found:

– On the southern edge of our study domain (southeastern U.S., Central Europe, southern Russia) the frequencies of freezing events decreased along with the duration of the cold season; – In the Arctic (North America, Europe, and North Atlantic north of 60°N), in some taiga areas of Russia, and at high elevations (The Tian Shan Mountains), the frequencies of freezing events increased “following” the expansion of the short warm season.

• Changes in the occurrence of freezing drizzle were estimated
• nly for Russia. We found a statistically significant nationwide

decrease in this element.

Vertical temperature gradients for freezing and no freezing day events between surface and 850 hPa.

T850 – Tsurface. Fennoscandia and northern parts of the U.S.

Climatology of freezing rain events over northern Europe

Annual frequency of moderate and heavy freezing events

Freezing rain days Freezing drizzle days

Changes of the mean annual numbers of days with freezing precipitation between 2005-2014 and 1975-2004 periods

F

Freezing rain days Freezing drizzle days

Changes of the mean annual numbers of days with intense freezing precipitation between 2005-2014 and 1975-2004

Intense freezing rain Intense freezing drizzle

Long-term regional mean values of freezing rain frequency over Norway and selected regions of North America and Russia for 1975-2014 and differences between the mean values for the last decade (2005-2014) and the previous 30-yr-long period (1975-2004)

Region Regional mean values days yr-1

• Diff. days

yr-1 Significant changes by following tests North America north of 66.7°N 1.8 1.06 t- & L- tests North America, between 50°N and 60°N 2.5 0.28 L-test & Rs- test North America, between 36°N and 50°N east of 95°W 4.0 0.05 North America south of 36°N, east of 85°W 0.8

• 0.21

t-test Norway south of 66.7°N 1.1 1.05 all three tests Norway north of 66.7°N 1.1 1.10 all three tests Russian Atlantic Arctic 1.4

• 0.20

L- & Rs- tests Northwest of the Great East European Plain 1.3 0.28 Northeast of the Great East European Plain 2.2 0.77 L- & Rs- tests Southwest of the Great East European Plain 4.2 0.32 Southeast of the Great East European Plain 1.8 0.28 Steppe Region of European Russia 4.3

• 1.30

L- & Rs- tests Northern Caucasia Steppes and Piedmont 2.1 0.16 Northern part of the forest zone of West Siberia 1.0 0.67 t-test Southern part of the forest zone of West Siberia 0.7

• 0.20

L- & Rs- tests Steppe zone of West Siberia 0.9

• 0.33

Statistically significant changes at the 0.05 level are in bold and at the 0.10 level are in bold italic

Global Annual Surface Air Temperature Anomalies, °C

Lugina et al. 2006, updated.

Anomalies from the long-term mean values for 1951-1975

Last 15 years Reid et al. 2016; in Global Change Biology

Future studies of freezing precipitation

.

Continue characterization of freezing events in

• Near surface temperatures and near surface atmospheric humidity
• Temperature and humidity profiles in the lower troposphere

Building a suite of meteorological variables that correspond to sufficiently high probability of freezing at the land surface and in the low troposphere:

• This suite can serve as a proxy for atmospheric conditions conducive for freezing

when in situ observations of freezing are not available

• Changes in these suite with time in the GCMs’ output will serve for projections
• f future frequency of freezing events