Martin Schroeder Utah Center

Simon Wang and Robert Gillies Utah Climate Center / Department of Plant, Soils, Climate Utah State University Two types of Column water vapor :

 Zonal/Midlatitude

 Pineapple Express Impact: In Northern Essentially all major historical have domain been associated with AR events.

(Dettinger, 2011)  Global warming  tropical belt widening  moisture increase

  Pineapple Express frequency? Reanalysis: Pros and Cons

•Uniform / global coverage (✔)

•Changing observations/computer systems (✖)  Questionable trend analysis Thus we need multiple reanalyses

1.NCEP/DOE Reanalysis I

2.NCEP/NCAR Reanalysis II

3.NOAA-CIRES 20th Century Reanalysis V2 (20CR)

4.ECMWF Interim Reanalysis (ERA-Interim)

1.NASA Modern Era Reanalysis for Research and Applications (MERRA)

2.NCEP Climate Forecast System Reanalysis (CFSR)

1. JRA-25 (not there yet)

Northern California High-Impact Cases:

11–24 February, 1986 (Leung and Qian 2009)

29 December, 1996 – 4 January,1997 (Galewsky, J., A. Sobel, 2005)

16–18 February, 2004 (Ralph, F. M., P. J. Neiman, G. A. Wick, S. I. Gutman, M. D. Dettinger, D. R. Cayan, and A. B. White, 2006)

29 December, 2005 – 2 January, 2006 (Smith, B.L., S.E. Yuter, P.J. Neiman, and D.E. Kingsmill, 2010)

Column water vapor flux & its streamfunction 

Precipitation (USMEX)  Composite PE events from multiple (6) Reanalyses

CompositesComposites of of PE PE events events from from Six Six Reanalysis Reanalysis Datasets Datasets CompositesComposites of of PE PE events events from from Six Six Reanalysis Reanalysis Datasets Datasets CompositesComposites of of PE PE events events from from Six Six Reanalysis Reanalysis Datasets Datasets U (200mb) 145 ° W Longitude WinterWinter U U (200mb) (200mb) 145 145 ° ° W W Longitude Longitude

Linear Trend Linear Trend Linear Trend Linear Trend Linear Trend Linear Trend

Linear Trend Linear Trend Linear Trend Linear Trend Linear Trend Linear Trend

Linear Trend Linear Trend Linear Trend Linear Trend Linear Trend Linear Trend

(0.1 mm/(0.1 day)mm/ (0.1 day)mm/ day)

Analysis of winter (Nov-Mar) 200mb U AnalysisAnalysis of of winter winter (Nov (Nov-Mar)-Mar) 200mb 200mb U U winds reveals a northward shift and windswinds reveals reveals a a northward northward shift shift and and weakening in the mid-latitude jet, weakeningweakening in in the the mid mid-latitude-latitude jet, jet, coinciding with a decrease in winter -1 -1 coinciding with a decrease in winter Vectors show magnitude and direction of water vapor flux (Q) (kg*m*s -*kg1 -)1 from selected coinciding with a decrease in winter VectorsVectors show show magnitude magnitude and and direction direction of of water water vapor vapor flux flux (Q) (Q) (kg*m*s (kg*m*s-*kg1*kg-)1 )from from selected selected precipitation over highhighVectors impact impact show days. days. magnitude and direction of water vapor flux (Q) (kg*m*s-1*kg-1) from selected precipitation over northern California high impact days. 2* -1* -1 precipitation over northern California Contourshigh impact show streamfunctiondays. or rotation/circulation of water vapor flux (Q) (m 2*s -1*kg -)1 during the same time period. Contours show streamfunction or rotation/circulation of water vapor flux (Q) (m 2*s -1*kg -)1 during the same time period. ContoursContours show show streamfunction streamfunction or or rotation/circulation rotation/circulation of of water water vapor vapor flux flux (Q (Q) )( m(m2*ss-1*kgkg-)1 ) during the same time period.

PE identification: Procedure

1.PE Index 2.PE pattern

Requisite conditions: • ( Z-mean>0) , • (Uq>75, Vq>50), (Uq>75, Vq>0) (upstream) (downstream) UQ

FOR 2 OR MORE CONSECUTIVE DAYS UQ

Z(hgt) PE identification: Procedure

1.PE Index 2.PE pattern

Spa al correla on: Pa ern recogni on L

H Criteria: scorr > 0.85

H L

L H

-1.0 0.0 1.0 4 Panel plot showing the frequency and linear trends in the number of Pineapple Express days per year and the 44 Panel Panel plot plot showing showing the the frequency frequency and and linear linear trends trends in in the the number number of of Pineapple Pineapple Express Express days days per per year year and and the the numbernumber of of Pineapple Pineapple Express Express events events per per year. year. All All days days meet meet criteria criteria set set out out in in PE PE Index Index number of Pineapple Express events per year. All days meet criteria set out in PE Index Winter Mean Precipitation Trend in Northern California (Oct-Apr)

(0.1 mm)

1980 2010

Declining Trend in Winter Precipitation (N.CA)

PE contribution to winter precip Residual winter precip

(mm)

Trend in precipitation

What accounts for the residual?

* Precip came from USMEX based on reanalysis “dates” Identify other synoptic patterns • Used ensemble of six reanalyses, daily means. • Manual identification for multiple types.

Zonal case composite Identify other synoptic patterns

LW trough Northwest flow

Zonal flow

Subtropical H SW trough Zonal flow Northwest flow Climatology SW trough LW trough Subtropical H Pineapple Express

% contribution frequency(days) % per day ~90% explained Zonal flow Northwest flow Trends: 1979-2010 SW trough LW trough Subtropical H Pineapple Express

% contribution Trend in storm type (%) Possible Mechanisms: U wind (DJF )

200mb U-wind change Possible Mechanisms:

Precipitation (Oct-Apr) Big Picture

• The widening of the tropical moisture band may lead to an increase in moisture availability for Pineapple Express .

• However, this does not translate into an increase in precipitation from Pineapple Express storms. Contrarily, precipitation linked to these storms is decreasing over northern California

• A northerly shift in the upper-level winter jet over the flux region coincides with the decrease in Pineapple Express storms and total winter precipitation in northern California.

Future Work

• Identify what effect the northerly shift and weakening of the winter jet may have on Pineapple Express contributions in and the Pacific Northwest.

References:

Leung L. R, and Y. Qian, 2009. Atmospheric rivers induced heavy precipitation and flooding in the Western U.S. simulated by the WRF regional climate model. Geophys. Res. Lett., 36, L03820, doi:10.1029/2008GL036445.

Galewsky, J., A. Sobel, 2005: Moist dynamics and orographic precipitation in northern and central California during the New Year's of 1997. Mon. Wea. Rev., 133, 1594-1612, doi:10.1175/MWR2943.1.

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: Role of atmospheric rivers. Geophys. Res. Lett., 33, L13801, doi:10.1029/2006GL026689.

Smith, B.L., S.E. Yuter, P.J. Neiman, and D.E. Kingsmill, 2010: Water vapor fluxes and orographic precipitation over northern California associated with a land-falling atmospheric river. Mon. Wea. Rev., 138, 74-100, doi:10.1175/2009MWR2939.1.

Dettinger, M. (2011), Climate Change, Atmospheric Rivers, and Floods in California – A Multimodel Analysis of Storm Frequency and Magnitude Changes. JAWRA Journal of the American Water Resources Association, 47: 514–523. doi: 10.1111/j.1752-1688.2011.00546.x