presntation_SCHICK_2010 Atmospheric Rivers

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Landfalling Impacts of Atmospheric Rivers:From Extreme Events to Long-term Consequences

Paul J. Neiman1, F.M. Ralph1, G.A. Wick1, M. Hughes1,J. D. Lundquist2, M.D. Dettinger3, D.R. Cayan3, L.W. Schick4,

Y.-H. Kuo5, R. Rotunno5, G.H. Taylor6

1NOAA/Earth System Research Lab./Physical Sciences Div., Boulder, CO2University of Washington, Seattle, WA

3U.S. Geological Survey, Scripps Institution of Oceanography, La Jolla, CA4U.S. Army Corp of Engineers, Seattle, WA

5National Center for Atmospheric Research, Boulder, CO6Oregon Climate Service, Oregon State University, Corvallis, OR

Presented at:The 2010 Mountain Climate Research Conference

Blue River, Oregon. 8 June 2010



Outline

1. Brief Review of ARs2. ARs as extreme weather events

3. Long-term impacts of ARs

4. Concluding RemarksA few acronym definitions:AR = atmospheric river IWV = integrated water vaporLLJ = low-level jet MSL = above mean sea levelSWE = snow water equivalent APDF = annual peak daily flow

NARR = North American regional reanalysis

Motivation: Atmospheric rivers (ARs) generate devastating floods, and also

replenish snowpacks and reservoirs, across the semi-arid West. Hence, it

is crucial to understand this key phenomenon, both as a major weather

producer and as one that contributes significantly to climate-scale impacts.



Zhu & Newell (1998) concluded in a 3-year ECMWF model diagnostic study:1) 95% of meridional water vapor flux occurs in narrow plumes in <10% of zonal circumference.2) There are typically 3-5 of these narrow plumes within a hemisphere at any one moment.3) They coined the term “atmospheric river” (AR) to reflect the narrow character of plumes.4) ARs constitute the moisture component of an extratropical cyclone’s warm conveyor belt.

5) ARs are very important from a global water cycle perspective.



Observational studies by Ralph et al. (2004, 2005, 2006) extend model results:1) Long, narrow plumes of IWV >2 cm measured by SSM/I satellites considered proxies for ARs.2) These plumes (darker green) are typically situated near the leading edge of polar cold fronts.3) P-3 aircraft documented strong water vapor flux in a narrow (400 km-wide) AR; See section AA’.4) Airborne data also showed 75% of the vapor flux was below 2.5 km MSL in vicinity of LLJ.

5) Moist-neutral stratification <2.8 km MSL, conducive to orographic precip. boost & floods.

IWV > 2 cmAtmos. river

cold air

warm air

400 km

Enhanced vapor fluxin Atmos. river

coldair

warmair



Global reanalysis melting-levelanomaly (hPa; rel. to 30-y mean)

Melting level ~4000 ft (1.2 km) abovenormal across much of the PacNW

during the landfall of this AR

Pacific Northwest Landfalling AR of early November 2006Neiman et al. (2008a)

~30”rain

SSM/I satellite imageryof integrated water vapor (IWV, cm)

This AR is also located near the leadingedge of a cold front, with strong vaporfluxes (as per reanalysis diagnostics)



Hydroclimatic analysis for the AR of 5-9 November 2006

Greatest 3-day precip.

totals during the periodbetween 5-9 Nov. 2006

>700 mm (28”)

>600 mm (24”)

Historical Nov. ranking for

the max. daily streamflowbetween 5-9 Nov. 2006

plus highmelting level

equals



Courtesy of Doug Jones , Mt Hood NF

Aftermath of flooding and a debris flow on the White River Bridge in Oregon

High-Impact Consequences!



• SSM/I satellite image shows AR.

• Frontal wave stalls AR on coast,causing prolonged heavy rains.• Stream gauge rankings for 17-

Feb-04 show regional extent ofhigh streamflow covering ~500 kmof coast.

• All 7 flood events on the RussianRiver between 1997-2006 weretied to land-falling ARs.

Russian River, CA Flooding250 mm of rain in 2 days

(Ralph et al. 2006)

Russian River flooding: Feb. 2004photo courtesy of David Kingsmill

AR stalls:heavy rains& flooding

Frontalwave

inflection



Given these results: What are the long-term hydrometeorological impacts oflandfalling ARs in western North America? Neiman et al. (2008b)

SSM/I Integrated water vapor (cm)

16-Feb-04;

p.m. comp.

IWV >2cm:<1000 km wide

IWV >2cm:>2000 km long

• Inspect 2x-daily SSM/I IWV

satellite composite images• 8 water years Oct97-Sep05:

• Identify IWV plumes >2 cm (0.8”):>2000 km long by <1000 km wide.

• AR landfall at north- or south-coast

• Focus on cool season when most

precip falls in western U.S., and onthe north-coast domain

1000 km

Approach: We developed a methodology for creating a multi-year AR inventory.



• The daily gridded NCEP–NCAR reanalysis dataset (2.5 x 2.5 ; Kalnay et al.1996) was used to create composite analyses during AR conditions – 29 dates.

• Composite reanalysis IWV plume oriented SW-NE from the tropical easternPacific to the coast.

• Composite plume situated ahead of the polar cold front.

• Wintertime ARs produce copious precip along coast, & frontal precip offshore.

• Reanalysis composites accurately depict the positions of the IWV plume and

precip. bands observed by the SSM/I composites... denoted by dotted lines.

Composite Mean Reanalyses – focus on North Coast Winter

IWV (cm) Daily rain (mm)Composite mean SSM/I axes

W i n t e r ( D J F )



• Strong vapor transport intersects coastline during winter, withmaximum on the warm side of the cold front.

• Transport originating from low latitudes

Composite Mean Reanalysis IVT (kg s-1 m-1) – North Coast winter



• Wintertime ARs are associatedwith trough/ridge couplet in the

mid-troposphere (~2-6 km MSL).

Composite Reanalysis Fields– North Coast WinterNorth-coast

5 0 0 h P a Z M e a n

( m )

9 2 5 h P a T A n o

m a l y ( C )

Wintertime ARs are associated withanomalous warmth at low levels.



Composite Winter Reanalysis Soundings at North Coast

Flow strengthenswith height...

...in pre-cold-frontalwarm-advection shear

Moisture decreaseswith height

Mountain top height

Max. moisture flux atmtn top... favors mtnprecip. enhancement.



1.8x the average snow accumulation

Sierras (119 sites)

snow pillow sites>1.5 km MSL

(~5000 ft)

Normalized Daily Precipitation and ΔSWE in CA* during DJF

Compared to the average of all precipitation days in the Sierra Nevada(observed by rain gauges and snow pillows), those days associated withlandfalling Atmospheric Rivers produced:

2.0x the average precipitation

*Qualitatively similar to, but quicker to explain than, north-coast results.



Seattle

HansonDam

Sauk

Queets

Satsop

Now let’s turn the problem on its head: What causes the largest annualrunoffs on major watersheds in western Washington? (Neiman et al. 2010)



Annual peak daily flows (APDFs) and atmospheric river (AR) events for WY1998-2009

AR non-AR [determined from 2x-daily SSM/I IWV satellite imagery]

APDF dates for WY 1998-2009

Green River Sauk River

Satsop River Queets River

46 of 48 annual peak daily flows in last 12 years at the 4 sites due to AR landfalls

Results consistent with Dettinger (2004) in CA: ARs yield daily increases instreamflow that are an order of magnitude larger than those from non-AR storms



Ranked APDFs for WY1980-2009 (NARR period)

Green River Sauk River

Satsop River Queets River

The APDFs occur most often Nov. - Jan.

T

o p

1 0

T

o p

1 0

Dates from the top-10 APDFs are used to create composite analyses from theNorth American Regional Reanalysis (NARR; Mesinger et al. 2006) to assess the

composite meteorological conditions that produced flooding in each of the 4 basins



Basin altitude attributes above gauges, and mean NARR top-10 melting-level altitudes**(300 m below 0°C altitude)

snow

rain

snowrain

snow

rain

snow

rain

mean mean

mean mean



Anomalously high melting levels + heavy precip = floods

NARR Composite Mean 2-day Precipitation (mm) for top-10 APDFs

(a) Green (b) Sauk

(c) Satsop (d) Queets



NARR Composite Mean Integrated Vapor Transports (kg s-1 m-1) for top-10 APDFs

(a) HHDW1 (b) SAKW1

(c) SATW1 (d) QUEW1



NARR Composite Mean Geopotential Heights (m) at 925 hPa for top-10 APDFs

(a) Green (b) Sauk

(c) Satsop (d) Queets



Seattle

Green

Queets

Sauk

Satsop



NARR Composite Mean profiles at coast for top-10 APDFs

weakstability

weakstability

Max. orographic forcingin AR conditions at

coast. Minimal terrainlift would place it inweakest stability –

optimal for heavy precip!

Green

Queets

SatsopSauk



Concluding Remarks

Atmospheric rivers (ARs) are long, narrow corridors of enhanced water vapor

transport responsible for most of the poleward vapor flux at midlatitudes.

Lower-tropospheric conditions during the landfall of ARs are anomalouslywarm and moist with weak static stability and strong onshore flow, resulting inorographically enhanced precipitation, high melting levels, and flooding.

Because ARs contribute significantly to precipitation, reservoir and snowpackreplenishment, and flooding in western North America, they represent a keyphenomenon linking weather and climate.

The highly 3-D character of the terrain in western Washington yields basin-specific impacts arising from landfalling ARs (i.e., strong dependence on flowdirection).

Next steps include quantifying the role of ARs in the global climate system andestimating the modulation of AR frequency and amplitude (and associatedextreme precipitation and flooding upon landfall) due to projected climatechange. Mike Dettinger is delving into this research (Dettinger et al. 2009).



References

Dettinger, M.D., 2004. Fifty-two years of “pineapple-express” storms across the west coast of North America. U.S.

Geological Survey, Scripps Institution of Oceanography for the California Energy Commission, PIER Energy-Related

Environmental Research. CEC-500-2005-004, http://www.energy.ca.gov/2005publications/CEC-500-2005-004/CEC-500-

2005-004.PDF, 15 p.

Dettinger, M.D., H. Hidalgo, T. Das, D. Cayan, and N. Knowles, 2009: Projections of potential flood regime changes inCalifornia: California Energy Commission Report CEC-500-2009-050-D, 68 p.

http://www.energy.ca.gov/2009publications/CEC-500-2009-050/CEC-500-2009-050-D.PDF.

Kalnay, E., and Coauthors, 1996: The NCEP/NCAR 40-year reanalysis project. Bull. Amer. Meteor. Soc., 77, 437-471.

Mesinger, F., and Coauthors, 2006: North American Regional Reanalysis. Bull. Amer. Meteor. Soc., 87, 343-360.

Neiman, P.J., F.M. Ralph, G.A. Wick, Y.-H. Kuo, T.-K. Wee, Z. Ma, G.H. Taylor, and M.D. Dettinger, 2008a: Diagnosis of an

intense atmospheric river impacting the Pacific Northwest: Storm summary and offshore vertical structure observed with

COSMIC satellite retrievals. Mon. Wea. Rev., 136, 4398-4420.

Neiman, P.J., F.M. Ralph, G.A. Wick, J. Lundquist, and M.D. Dettinger, 2008b: Meteorological characteristics and overland

precipitation impacts of atmospheric rivers affecting the West Coast of North America based on eight years of SSM/I

satellite observations. J. Hydrometeor ., 9, 22-47.

Neiman, P.J., L.J. Schick, P.J. Neiman, F.M. Ralph, M. Hughes, and G.A. Wick, 2010: Flooding in western Washington: The

connection to atmospheric rivers. J. Hydrometeor ., 11, to be submitted.

Ralph, F.M., P.J. Neiman, and G.A. Wick, 2004: Satellite and CALJET aircraft observations of atmospheric rivers over the

eastern North-Pacific Ocean during the winter of 1997/98. Mon. Wea. Rev.,132

, 1721-1745.Ralph, F.M., P.J. Neiman, and R. Rotunno, 2005: Dropsonde Observations in Low-Level Jets Over the Northeastern Pacific

Ocean from CALJET-1998 and PACJET-2001: Mean Vertical-Profile and Atmospheric-River Characteristics. Mon. Wea.

Rev., 133, 889-910.

Ralph, F.M., P.J. Neiman, G.A. Wick, S.I. Gutman, M.D. Dettinger, D.R. Cayan, and A.B. White 2006: Flooding on

California’s Russian River: The Role of Atmospheric Rivers. Geophys. Res. Lett., 33, L13801, doi:10.1029/2006GL026689.

Zhu, Y., and R.E. Newell, 1998: A proposed algorithm for moisture fluxes from atmospheric rivers. Mon. Wea. Rev., 126,

725-735.

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