Observing Networks, Precipitation and Extreme Precipitation
Paul H. WhitfieldMeteorological Service of CanadaDepartment of Earth Sciences, Simon Fraser University
Can we learn more about extremes [and climatology in general] from networks of stations rather than single stations?
What do we learn when the 100 year event happens at one location?
• Background
• Multiple site precipitation
• Multiple site extremes
• Pineapple Express
A scheme for precipitation measures at two locations (Toews et al. 2009)
Multi-site Precipitation
Precipitation has many types (drizzle, hail, virga, graupel).
For some meteorological & climatological applications, it can be classified into:
Convective vs. stratiform
(Based on mechanisms of genesis)
And for some other applications
(e.g., Hydrology):
Local vs. regional:
(Based on distribution and impact)
Algorithms
Let PX and PY be daily precipitation amounts at X and Y
η =PX / PY (1)
For a suitable η > 1, η ≥ η ≥ η-1 is regarded as regional
Otherwise as local
Or λ = max(PX, PY) / (PX + PY) (2)
For a suitable λ > 0.5, λ > λ is regarded as local
λ ≤ λ is regarded as regional
Algorithms
• For precipitation measures
at multiple (M) locations,
(3)
where M is number of locations with precipitation (M ≥ 2), MH ≤ M / 2,
And P represents the precipitation amount, P1 ≥ P2 ≥ ··· ≥ PM ,
For a suitable Λ > 0.5, Λ > Λ is regarded as local
Λ ≤ Λ is regarded as regional
M
mm
M
mm
H
PPM
M H
112
Applications• The Dongting Lake Basin
Subtropical monsoonal
climate, wet in summer.
• The BC Inner South Coast
Mid-latitude coastal
climate, wet in winter.
Data• Daily precipitation data from the 10 climate stations
(1979 – 2008)
• NCEP/DOE AMIP-II Reanalysis datasets
(2.5°x2.5° grid, every 6 hrs) Wet season: 9 Apr – 8 Jul (DLB-HP) and 1 Nov – 30 Jan (ISC-BC)
Dry season: 15 Nov – 13 Feb (DLB-HP) 19 Jun – 17 Sep (ISC-BC)
Multi-Location Scheme
( 0.5 ≤ Λ ≤ 1 )
All year round
DLB-HPCross plots of daily precipitation between two of five selected climate stations in using a log-log scale.
Based on Eq. (2) with λ = 0.75
• Regional events
• Local events
Regression lines
Wet Season
DLB-HPCross plots of daily precipitation between two of five selected climate stations in using a log-log scale.
Based on Eq. (2) with λ = 0.75
• Regional events
• Local events
Regression lines
Dry Season
DLB-HPCross plots of daily precipitation between two of five selected climate stations in using a log-log scale.
Based on Eq. (2) with λ = 0.75
• Regional events
• Local events
Regression lines
(Multi-Location scheme with Λ = 0.75) Composites and anomalies from climatology
1333 Local
318 Regional
(Multi-Location scheme with Λ = 0.75) Composites and anomalies from climatology
777 Local
331 Regional
(Multi-Location scheme)
(with Λ = 0.75)
Climatological mean
850-hPa moisture flux & divergence
Composite local events:
Composite regional events:
All year round
ISC-BCCross plots of daily precipitation between two of five selected climate stations in using a log-log scale.
Based on Eq. (2) with λ = 0.75
• Regional events
• Local events
Regression lines
Wet Season
ISC-BCCross plots of daily precipitation between two of five selected climate stations in using a log-log scale.
Based on Eq. (2) with λ = 0.75
• Regional events
• Local events
Regression lines
Dry Season
ISC-BCCross plots of daily precipitation between two of five selected climate stations in using a log-log scale.
Based on Eq. (2) with λ = 0.75
• Regional events
• Local events
Regression lines
(Multi-Location scheme with Λ = 0.75) Composites and anomalies from climatology
1620 Local
577 Regional
(Multi-Location scheme with Λ = 0.75) Composites and anomalies from climatology
1128 Local
90 Regional
(Multi-Location scheme)
(with Λ = 0.75)
Climatological mean
850-hPa moisture flux & divergence
Composite local events:
Composite regional events:
Pineapple Express?
Extremes
Multi-Location Scheme
( 0.5 ≤ Λ ≤ 1 )
At least one station p>25mm
All year round
DLB-HPCross plots of daily precipitation between two of five selected climate stations in using a log-log scale.
Based on Eq. (2) with λ = 0.75
• Regional events
• Local events
Regression lines
At least one station p>25mm
(Multi-Location scheme with Λ = 0.75) Composites and anomalies from climatologyAt least one station p>25mm
331 Local
182 Regional
(Multi-Location scheme with Λ = 0.75) Composites and anomalies from climatology
At least one station p>25mm
27 Local
45 Regional
All year round
ISC-BCCross plots of daily precipitation between two of five selected climate stations in using a log-log scale.
Based on Eq. (2) with λ = 0.75
• Regional events
• Local events
Regression lines
At least one station p>25mm
(Multi-Location scheme with Λ = 0.75) Composites and anomalies from climatology
At least one station p>25mm
218 Local
183 Regional
(Multi-Location scheme with Λ = 0.75) Composites and anomalies from climatology
At least one station p>25mm
55 Local
11 Regional
Pineapple Express
Pineapple Express
Pineapple Expressa weather condition made of a jet stream of wet, warm air that reaches western North America from the Pacific Ocean, usually by way of Hawaii, and causes
heavy rainfall.
November 2006 flood, Granite Falls on the Stillaguamish River
Lake Bad Water – Death Valley Winter 2005
Pineapple Express
Mean seasonal cycles of the timing of pineapple-express circulations (bars) and the latitude of the jet stream core (maximum wind speeds at 250 hectopascals (hPa) pressure levels) north of Hawaii (curve); notice that the timing histogram has been reversed for comparison to the latitude curve.
Relations (a) between the NINO3.4 sea-surface temperature (SST) index of the El Niño-Southern Oscillation and the sum of water-vapor transports (Table 1) by pineapple-express circulations, and (b) between the Pacific Decadal Oscillation (PDO) index and the circulations. Red dots indicate (a) El Niños and (b) El Niño-like PDO years; blue dots indicate (a) La Niñas and (b) La Niña-like PDO years; green dots are neutral years. Lines are regression fits.
Exceedance probabilities for day-to-day changes in December–February discharges in the Merced River at Happy Isles, Yosemite National Park, under various circulation and precipitation conditions.
Det
tinge
r 20
04
Climate/weather questions:
• Does the distance from the jet stream affect the intensity? During events stations outside the ‘front’ should have less precipitation than those along the band. Using real observations can we detect if this is true? This needs a new way to structure data.
• Determine relative frequency of events in observations across a sample space of the climate network with some augmentation for the first 100 km south of Canada
• Effect of the Pineapple Express should both decrease with distance from the coast and have some significant effects in some regions of the interior. Is this more prevalent in some locations?
• Does the angle of transit affect intensity of precipitation [i.e. does it explain Tropical Punch?]
• Can we understand better the connection to ENSO and PDO to occurrence?
• Will these events change in a warmer climate – is there a way to tease out any part of the pineapple express variability to warmer/cooler periods/years?
Flood/streamflow questions:
• Does the distance from the jet stream affect the intensity? During events stations outside the ‘front’ should have less precipitation than those along the band. Using real observations can we detect if this is true? This needs a new way to structure data.
• Determine relative frequency of events in observations across a sample space of the climate network with some augmentation for the first 100 km south of Canada
• Effect of the Pineapple Express should both decrease with distance from the coast and have some significant effects in some regions of the interior. Is this more prevalent in some locations?
• Does the angle of transit affect intensity of precipitation [i.e. does it explain Tropical Punch?]
• Can we understand better the connection to ENSO and PDO to occurrence?
• Will these events change in a warmer climate – is there a way to tease out any part of the pineapple express variability to warmer/cooler periods/years?
Discussion questions:
• Will climate change shift the landing of Pineapple Express northward?
• Can information from multiple sites be useful in validating models?
• Can we apply EVT to multiple stations?
• How to deal with processes that are important at local scale and not resolved in GCM?