Bodo Bookhagen

Geography Department, University of California, Santa Barbara

ENSO, orographic barriers, and TRMM rainfall along the eastern Andes

Rainfall along the Andes – TRMM2B31

Bookhagen and Strecker, 2008

TRMM platform

PR Precipitation Radar

TMI TRMM Microwave Imager

VRS Visible Infrared Scanner

LIS Lightning Image Sensor

CERES Cloud and Earth’s Radiant Energy System

•High-resolution weather parameter measurement between 36°N and 36°S

•Several instruments on the platform

•Followed by the GPM (Global Precipitation Measurement) project

Calibration – TRMM2B31

Bookhagen and Strecker, 2008

Calibration of TRMM rainfall

Bookhagen and Burbank, in review

Validation – TRMM2B31 and TRMM3B42

TRMM 3B42 – combination of several satellite products scaled to match gauge data Bookhagen and Strecker, 2008

Rainfall variations along the Andes

North and south of 17°S – TRMM2B31

elevation asl (km), m

ean annual rainfall (m/yr),

3-km-relief (km

)

North and south of 17°S – TRMM3B42

elevation asl (km), m

ean annual rainfall (m/yr),

3-km-relief (km

)

North and south of 17°S – relief

elevation asl (km), m

ean annual rainfall (m/yr),

3-km-relief (km

)

Rainfall along the Andes – all swaths

Rainfall along the Andes – all swaths

Río Pastaza

Fitzcarrald arch

Rainfall along the Andes – all swaths

Rainfall along the Andes – relief relation

Rainfall along the Andes – relief relation

Rainfall along the Andes – relief relation

Rainfall along the Andes – relief relation

Santa María Basin, NW Argentina (~27°S)

Relief-Rainfall Relationship

Simplified geologic structure of eastern Andes margin north of ~17°S

Simplified geologic structure of eastern Andes margin at ~25°S

Rainfall in the Andes knee (orocline)

Impact of ENSO on South America

ENSO oscillations

BEST index is a combination of (1) an atmospheric component of the ENSO phenomenon (the Southern Oscillation Index or "SOI") and (2) an oceanic component (Nino 3.4 SST, which is defined as the SST averaged over the region 5N-5S and 170W to 120W), defined by Smith and Sardeshmukh, 2000

Note: No change of pos. or neg. ENSO events if Multivariate ENSO Index is used (MEI)

TRMM 3B42 – mean monthly rainfall

3-hr time intervals achieved through a combination of observations from several satellite platforms (TRMM, SSM/I, AMSR, AMSU)

data combined with some ground-station data and gridded to 0.25x0.25° ~30x30km)

Validation – TRMM2B31 and TRMM3B42

TRMM 3B42 – combination of several satellite products scaled to match gauge data Bookhagen and Strecker, 2008

TRMM 3B42 – neg. ENSO

TRMM 3B42 – pos. ENSO

TRMM 3B42 – pos. ENSO anomaly

TRMM 3B42 – neg. ENSO anomaly

TRMM 3B42 – neg. ENSO 3-day anomaly

Determining rainfall intensity

•analyze the timeseries of each pixel separately (>30,000 measurements) by first calculating cumulative rainfall amounts, which integrate rainfall over the previous 1, 2, 3, or 5-day periods (‘smoothing’)

•Identify mean of each pixel timeseries

•Count number of events above mean

By varying the integration timescale from 1 to 5 days, we take into account the different storm timescales: we observe that the integration over longer time periods (3 or 5 days) limits the relative storm occurrence to the elevated Andes and the Altiplano-Puna Plateau, suggesting that longer lasting storms occur more frequently there.

TRMM 3B42 – neg. ENSO 5-day anomaly

TRMM 3B42 – neg. ENSO 3-day anomaly

TRMM 3B42 – pos. ENSO 3-day anomaly

TRMM 3B42 – no ENSO 3-day anomaly

Drainage Subbasins of the Amazon

Drainage Subbasins of the Amazon

Drainage Subbasins of the Amazon