(average ratio is 1.76)
DESCRIPTION
WINTER OROGRAPHIC-PRECIPITATION PATTERNS IN THE SIERRA NEVADA—CLIMATIC UNDERPINNINGS & HYDROLOGIC CONSEQUENCES Mike Dettinger 1 , Kelly Redmond 2 , & Dan Cayan 1 1 U.S. Geological Survey Scripps Institution of Oceanography La Jolla, CA 2 Western Regional Climate Center, DRI, Reno. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/1.jpg)
WINTER OROGRAPHIC-PRECIPITATION PATTERNS IN THE SIERRA NEVADA—CLIMATIC UNDERPINNINGS & HYDROLOGIC CONSEQUENCES
Mike Dettinger1, Kelly Redmond2, & Dan Cayan1
1 U.S. Geological SurveyScripps Institution of OceanographyLa Jolla, CA
2 Western Regional Climate Center, DRI, Reno
![Page 2: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/2.jpg)
1910 1920 1930 1940 1950 1960
Starting Year
1970 1980 1990 20000.50
1.00
1.50
2.00
2.50
3.00
Tahoe City / Sacramento Ratio
Ratio of June thru July PrecipitationTahoe City / Sacramento. 1909-10 thru 2000-01.Blue: 7-year running mean.
2001-02 :~1.7 thru Feb
(Average Ratio is 1.76)
![Page 3: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/3.jpg)
1910 1920 1930 1940 1950 1960
Starting Year
1970 1980 1990 20000.50
1.00
1.50
2.00
2.50
3.00
Tahoe City / Sacramento Ratio
Ratio of June thru July PrecipitationTahoe City / Sacramento. 1909-10 thru 2000-01.Blue: 7-year running mean.
2001-02 :~1.7 thru Feb
Why should we care?
Most of our water comes from high altitudes, and yet most of our observations of precip come from low elevations.
![Page 4: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/4.jpg)
Also, the strength of orographic gradients influences runoff timing and the sizes of floods.
Simulated Runoff Responses to Imposed Orograpic Gradients North Fork American River, Sierra Nevada 1983
![Page 5: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/5.jpg)
SimulatedSnowpack Changes with Imposed Orograpic Gradients North Fork American River, Sierra Nevada 1983
Basinwide
High vs low
--> Basinwide snowmelt comes earlier
![Page 6: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/6.jpg)
So, how and why does the ratio of precipitation at low- and high-altitude stations on the west slope of the Sierra Nevada vary?
High-altitude site
Low-altitude site
![Page 7: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/7.jpg)
+/- 10%?925 mb
Surface
850 mb
700 mb
300 mb
+
+
+
Water-vapor transport rates and directions were vertically integrated from surface to 300 mbars each day , 1948-2000, in the NCEP/NCAR Reanalysis products to arrive at a daily transport vector through each grid cell
(assuming linear variation of q, u, & v between levels)
+
+
…
q v dp/g =
![Page 8: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/8.jpg)
Transport vectors provide a focused perspective on storm-time thru seasonal-scale circulations & conditions
(New Years 1997)
![Page 9: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/9.jpg)
Differences between the averages of transports during 180 LARGE-STORM DAYS vs 180 SMALL-STORM DAYS, Dec-Feb 1949-99
L
![Page 10: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/10.jpg)
Differences between the averages of transports during 180 STRONGLY OROGRAPHIC STORMS vs 180 WEAKLY OROGRAPHIC STORMS, Dec-Feb 1949-99
L
![Page 11: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/11.jpg)
14 Low Ratio Winters
Composite
October-March
700 mb Departures
11 High Ratio Winters
![Page 12: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/12.jpg)
No obvious “special” layers or reversals to prohibit vertical averaging, at least in the means.
![Page 13: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/13.jpg)
Locally, orographic storms (winds) blow from somewhat more westerly directions than do “large” storms.
MODE OF OROGRAPHIC STORMS
MODE OF LARGE STORMS
IN MAP VIEW:
![Page 14: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/14.jpg)
Thus, orographic storms are NOT always the largest…
Although, almost by definition, they often are large.
![Page 15: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/15.jpg)
LL
Transport paths significantly associated with El Ninos
![Page 16: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/16.jpg)
La Nina storms are strongly inclined towards “orographic” approaches…
So they provide more of the most strongly orographic storms.
![Page 17: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/17.jpg)
Mean 1.76
-2.5 -2.0 -1.5 -1.0
June - Nov SOI
-0.5 0.0 0.5 1.0 1.5 2.0
1.00
1.50
2.00
2.50
3.00
TahoeCity / Sacramento Ratio
Ratio of Tahoe City / Sacramento Precipitation, July thru Juneversus June-November Southern Oscillation Index.1909-1910 thru 2000-2001. N = 68. r = 0.37 (p < .01) Mean 1.76.
7 9
51416
17
![Page 18: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/18.jpg)
Transport paths associated with North Pacific decadal variations
LL
![Page 19: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/19.jpg)
Despite large looking correlations, PDO modifies storm directions and orographic gradients only modestly.
![Page 20: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/20.jpg)
This approach might even be used to project how orographic precipitation would be under global warming scenarios.
e.g., PCM ---> marginally weaker orography
![Page 21: (Average Ratio is 1.76)](https://reader035.vdocument.in/reader035/viewer/2022070410/568146af550346895db3cbd7/html5/thumbnails/21.jpg)
Winds that carries moisture directly across the range yields most precipitation, but orographic influences may require a bit more westerly approaches.
La Ninas (and, perhaps, negative PDOs) may provide slightly more orography as a result.
Other factors being equal, stronger orographic gradients yield later snowmelt & river discharge; weaker gradients threaten larger flood peaks.
CONCLUSIONS
Wet
!
Orographic!