Analysis of climate trends in tropical rainfall C.-H. Sui - - PowerPoint PPT Presentation

Analysis of climate trends in tropical rainfall

C.-H. Sui 隋中興 隋中興 隋中興 隋中興 J.-J. Sun 孫既仁 孫既仁 孫既仁 孫既仁

• Dept. of Atmospheric Sci., National Taiwan Univ

Peng Liu 刘鹏 刘鹏 刘鹏 刘鹏 Nanjing Univ. of Information Science and Technology

Analysis of climate trends in tropical rainfall

• I. Global-Scale Features of Multidecadal Trends
• II. Climate Trends in Rainfall

Observed climate variations (forced component) and (free component) (by GHS, aerosols, SW), (due to coupled climate processes) The two components can be further divided as thermodynamically induced dynamically induced Forced residual Dynamical Contribution Free

• Fig. 3

EOF (Low-pass filtered, detrended SSTA)

1st mode HadISST 2nd mode HadISST 2nd mode ERSST 1st mode ERSST Primarily a Pacific oscillation Primarily an Atlantic oscillation 1990 1970 1950 1930 1910 1890 1990 1970 1950 1930 1910 1890 60 yrs 20 yrs 60 yrs

Pacific Decadal Oscillation Atlantic Multidecadal Oscillation

PDO ( ~ 55 yr , ~ 20 yr) AMO (~ 65 yr)

1

Combined EOF WOD, NCEP (U, V, w, Z, T, Q) at 8 pre. levels ERA40

Linear trend 1980-2009 (K/30yr)

a

Regressed T2m on the 1st PC (the PDO-like) from HadISST EOF analyses

a

Regressed T2m on the 2nd PC (the AMO-like) from HadISST EOF analyses

N S

↗ Northward Ocean Heat Transport ↘ Northward Atm Heat Transport

Hadley cell strengthening & Northward shift of ITCZ AMO phase

• - ↗ +tive

Walker circulation strengthening PDO phase +tive ↘ --

stream func./NCEP Contour (1980-2007 mean) Shadings (2007-1994) minus (1993-1980) [unit:1010kg/s]

Liu and Sui (2013) STgm GISS [SAT GHCN, HadISST1 1880-Nov 1981, NOAA OISSTv2, Dec 1981-present]

The Partial Least Squared (PLS) Regression Analysis

Predictors: Xij ( j denotes grids in space) Predictant: Yi ( i denotes time) The PLS-regression method seeks to predict Y with the predictors (a linear combinations of X) and to maximize (1) variance in Y , and (2) correlation between X and Y

Centennial trends in original (R0) & PLS-regressed (RPLSR) rainfall time series at four stations in Taiwan

[ ERSST (1900~2011) is used in PLS regression ] Taipei Tainan Hentsung Taidon Mean

(mm/d)

5.10 5.28 6.63 5.42 R0

(% /100yr)

12.6

• 14.2
• 28.6
• 13.7

RPLSR

(% /100yr)

7.4 0.1 0.1

• 3.5

SSM/I rainfall data for the period of 1988-2009

Mean rainfall Trend in Rainfall amount (mm/day per decade) Trend in Rainfall Intensity (% per decade) “ rich → richer, poor→poorer”

• verall increasing

tendency

SSMI GPCP Es+(∇• ∇• ∇• ∇•qv)b Es (∇• ∇• ∇• ∇•qv)b Mean (mm/d) 3.62 2.92 3.72 4.49

• 0.77

trendoriginal (% /decade) 1.9 0.53 2.47 2.38 1.9 trendPLSR (% /decade)

• 0.8
• 0.73
• 0.1
• 0.23
• 1.25

Trends in rainfall amount over tropical oceans 1988-2009

SSMI

SSMI GPCP

Trends in original data (Ro) Trends in original data (Ro) Trends in PLS regressed data (Ro) Trends in PLS regressed data (Ro)

Decadal trends in rainfall amount over tropical oceans (30oS-30oN)

dw n p dw n p p dw n p p

w w w w w w

• ⋅

∆ + ∆ ⋅ = ∆

• ⋅

=

(1995-2010)−(1979-1994)

dr n p dr n p p dr n p p

r r r r r r

• ⋅

∆ + ∆ ⋅ = ∆

• ⋅

=

20N 10N 10S 20S

GPCP: (1995-2010)− − − −(1979-1994) SSMI V7: (2000-2011)− − − −(1988-199

(1995-2010)− − − −(1979-1994)

Global-Scale Features of Multidecadal Trends Two dominant modes : PDO/IPO and AMO. PDO-like oscillation : ENSO-like and hemispheric symmetric AMO : hemispheric asymmetric In recent decades since 1980 The two oscillations contribute significantly to the increasing trends in STgm [almost half of the warming ] (Liu and Sui 2013)

Conclusions - I

In recent years 1988-2009 Decadal oscillations contribute significantly to an increasing general circulation.

• 1. Trends in PLS regression analysis:

“dynamic part of rain amount ” major cause of “rich→ → → →richer” “residual rain amount ” weakening

• 2. Trends in w-rain combined analysis:

“thermodynamic part of heavy rain” overall increasing Caution: reliability limited by the short record of data

Conclusions - II

As the climate warms:

Held and Soden (2006) radiative cooling ↗ → subsidence ↗ Good global constraints , How about tropics where deep and shallow clouds respond to climate forcing differently ?

• Obs. Rainfall record , short, mix with multiscale oscillations

Stephens and Ellis (2008)

) 6 . ~ (b W W b R R ∆ ≈ ∆

1

07 . /dT ln , / /

−

≈ ≡ + = K e d T M M P P

s

α αδ δ δ

Mass exchange between the boundary layer & free troposphere

－300K ---305K

4%/K 8%/K CWV BWV 5%/K~1%/0.2K~1%/decade (C. J. Muller & P. A. O’Gorman 2011) 99.9% 99.99% BWV

CRM : The Physic of Precipitation

The earth’s surface temperature warmed by 0.19±0.04K/decade according to the Global Historical Climatology Network between 1987-2006

More Precipitation Extreme?

(D. M. Romps , 2010)

Time series of boreal summer (MJJAS) mean indices

Wang et al. 2013 PNAS

U850 averaged over the equatorial Pacific (10°S–10°N, 140°E–120°W) .

(mm·d−1) averaged over the entire NH monsoon rainfall domain (U850-U200) ave (0°–20°N, 120°W–120°E)

(r = 0.85)

• Max. |cross-equatorial, zonal mean meridional mass stream

function (1010 kg·s−1)| ERAI and GPCP, version 2.2, 1979–2011

Domain: 30S-30N Detrended SST by 30S-30N mean trend 30S-30N Mean: 3.6175(mm/day)

(a) Time series of the averaged values over tropical oceans (30oS-30oN) for the

• riginal GPCP rainfall (R0, red), and the residual rainfall after a partial least

squared regression analysis (PLSRA) applied to SST and rainfall fields to suppress the natural oscillations in precipitation data (after the first and second PLSRA, R1 in green and R2 in blue). The dashed lines indicate the corresponding linear trends. (b) The same as (a) except for SSM/I Units in mm d-1. 2.92 0.53 %

• 0.73 %

(10y)-1 3.62 1.9 %

• 0.8 %

(10y)-1

GPCP Qbdy EVP Qconv

mean 2.92 3.72 4.49

• 0.77

R0 0.53 2.47 2.38 1.9 R1 0.29 0.39 0.36

• 1.1

R2

• 0.73
• 0.1
• 0.23
• 1.25

% (10y)-1

SSMI GPCP Es+(∇• ∇• ∇• ∇•qv)b Es (∇• ∇• ∇• ∇•qv)b Mean (mm/d) 3.62 2.92 3.72 4.49

• 0.77

trendoriginal (% /decade) 1.9 0.53 2.47 2.38 1.9 trendPLSR (% /decade)

• 0.8
• 0.73
• 0.1
• 0.23
• 1.25

Decadal trends in rainfall amount over tropical oceans

SSMI

SSMI GPCP

Trends in original data (Ro) Trends in original data (Ro) Trends in PLS regressed data (Ro) Trends in PLS regressed data (Ro)

1.9 0.53 %DY

20N 10N 10S 20S

GPCP: (1995-2010)− − − −(1979-1994) SSMI V7: (2000-2011)− − − −(1988-199