Tropical Moisture Exports and Extreme Rainfall
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Transcript of Tropical Moisture Exports and Extreme Rainfall
Tropical Moisture Exports and Extreme Rainfall
Mengqian Lu and Upmanu LallEarth and Environmental Engineering, Columbia University, NY, NY, United States.
Columbia Water Center: Global Flood Initiative
Flood Risk and Changing Climate Typical Hypothesis: Since the water holding
capacity of the atmosphere increases with warming, extreme rain events will become more frequent
But where … and in which seasons? Are most extreme floods over large basins due to
local convection or large scale moisture transport? What aspects of circulation are important for
floods? Specifically, what role is played by organized
tropical moisture exports (TME)?
AV. ATMOSPHERIC MOISTURE TRANSPORT ASSOCIATED WITH THE TOP 10 FLOODS AT DIFFERENT LOCATIONS
Source: Hyun-Han Kwon
Columbia Water Center Global Flood Initiative
Major TME Source regions and their seasonality for N Hemisphere1979-2011
Knippertz & Wernli 2010, 2013
50˚N
45˚N
46˚N
47˚N
48˚N
49˚N
3˚W4˚W5˚W 2˚W 1˚W
High:420Low:-81 (m)
Brittany
A Flood in France & Germany in January 1995 Lu et al 2013
The TME Train Day by DayLu et al 2013
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1st 6th 11th 16th 21st 26th 31st
No. of TracksΔQ (g/kg)
TME birth date in January 1995
No. of Tracks entered the areaTotal Specific Humidity Released
Daily TME’s entering the French region and associated Specific Humidity release for the French region
Lu et al 2013
17 Jan 1995 to 28 Jan 1995 mid-latitude daily SLP anomaly field evolution Lu et al 2013
(a)
(b)
Leading PC modes of mid-latitude daily January Sea Level Pressure fields that are correlated with January rain in the French regionDiagnosed from MERRA January data excluding 1995
GLM based prediction of area averaged daily rainfall using SLP PC’s Model built without using January 1995 data 53% variance explained in out of sample prediction
Lu et al 2013
Back to the USA…………
Where do the storm tracks for the N. E. USA come from?
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
-0.8
-0.6
-0.4
-0.2
0
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Monthly Correlation with number of tracks entering Northeast USA
Days with Rain>90%Days with Rain<10%Monthly DQ
Corre
latio
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1989-2010 data
Major TME Source regions and their seasonality for N Hemisphere1979-2011
Knippertz & Wernli 2010, 2013
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
-0.10
0.00
0.10
0.20
0.30
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0.60 Probability of a Track entering the NE from a given source by Month
P(NE|PE)P(NE|WP)P(NE|GS)P(NE|GP)
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec0.00
0.10
0.20
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0.40
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Probability that a track entering the NE came from a particular source by month
P(PE|NE)P(WP|NE)P(GP|NE)P(GS|NE)
FLOODS EXCEEDING THE 10 YEAR FLOOD ACROSS OHIO RIVER SUB-BASINS
Robertson et al, 2013
(a) Vertically integrated 600 mb - surface moisture flux in kg m s-1 (strongest 20 percent of values shown as arrows) and moisture convergence in gm-2s-1 (contours) for drainage basins (size > 103 km2) within the Ohio Valley averaged over the nine days leading to the 10-year flood.
Full field Anomaly
Nakamura et al, 2013
Large-scale anti-cyclonic moisture flow & convergence (Bermuda High)
700 mb geopotential height anomalies (in m) in contours and vertical pressure velocity (in mb day-1) colors (blue/purple is upward motion).Left: 20 event averageRight: April 2011
Nakamura et al, 2013
The dipole pattern of a significant positive geopotential high anomaly to the east of the flooded basins together with a weaker but negative anomaly to the west, are established on day -9 and persist throughout the days leading to the flood event.
Summary• Our exploratory analyses suggest that persistent, consistent
anomalous circulation and moisture transport patterns may determine large floods in a specific region implications for climate scenario “downscaling” and prediction.
• Tropical Ocean moisture sources and associated circulation patterns that focus meridional transport into the US Midwest, along the East coast, and into N. Europe can be identified even across event composites. flood determinism ?
• For such events, persistent wave like patterns and synoptic circulation types potentially related to ENSO and MJO activity may be identified Tropical SST/OLR Anomalies?
• Short to medium range probabilistic forecasts of the extreme events, as well as seasonal stochastic simulation may be feasible, and are being explored.
Columbia Water Center Global Flood Initiative