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El Niño and La Niña refer to abnormal cold and warm sea
surface temperature (SST) events respectivelly, which initiate along the
western coast of Peru and expand west to the central equatorial Pacific Ocean. Scientists have found that El Nño and La Niña have profound
effects on weather and climate in the whole tropics and subtropics, as well
as in the middle and high latitudes. To understand El Niño /La
Niña and further predict them is a challenging task, and needs to
treat the ocean and the atmosphere above as an integrated system: SST
affects the atmosphere mainly by providing latent heat and sensible
heat fluxes; and the atmosphere behavior, such as wind and precipitation,
in turn, affects SST. Scientists gain their knowledge of El Niño and
La Niña by analyzing observed data and carring out the experiements with
numeric atmospheric, ocean, or coupled ocean-atmosphere general circulation models.
It is well known that the low-frequency variation of tropic precipitation
with an irregular 4-5 year period is mainly corresponding to SST cold/warm
events. TRMM data by themselves provide a uniquely accurate rainfall data set,
but the sampling becomes inadequate for short intervals and small areas.
However, by combinining TRMM data with other satellite rainfall estimates and
rain gauge analysis, the product TRMM 3B43, titled TRMM Other Data Source, extends TRMM-like accuracy to finer space and time resolutions.
Scientists have shown that TRMM rainfall data document the
interannual variability during 1998-2000. The following figure depicts
the El Niño and La Niña signature in the TRMM 3B43 data.
The top panel is the two-month mean rainfall rate (mm/month) for
Jannuary and February 1998 over the tropical and subtropical regions.
Heavy rainfall appears over the South Pacific Convergence Zone (SPCZ),
South Indian Ocean, and the South America. The bottom
one is the difference in the two-month mean rainfall between 1999 and 1998
(subtracting the mean of 1998 from that of 1999).
The difference figure shows a typical ENSO patterns in precipitation field
corresponding to El Niño and La Niña events of SST.
To see this relation clearly, the SST anomaly (C o) averaged on the 5S-5N belt is plotted on the longitude (horizontal axis) and time (vertical
axis) dimension below.
This SST anomaly figure depicts the peak of the 1997-1998 El Niño at
the start of the year and the entry into the 1998-1999 La Niña by the
end of the year. The corresponding changes in the tropical precipitation field
are characterized by a dipole pattern: a belt with reduced precipitation from
the eastern equatorial Pacific Ocean to the Central part, and an area with
increased precipitation over the western Pacific Ocean and the southwestern
Pacific Ocean.
Scientists at GSFC explore the use of TRMM precipitation
data in their numerical ocean model simulation. With TRMM precipitation data
as an input, their model reproduces the real SST variations over the Indian
ocean, as well as over the eastern equatorial Pacific and the equatorial
Atlantic Oceans, for the El Niño period of fall 1997 to spring 1998.
TRMM data successfully document the interannual precipitation variation,
coordinating the SST changes beneath the atmosphere.
Reference:
Murtugudde, R., J.P., McCreary Jr., A.J., Busalachi, 2000: "Oceanic processes
associated with anomalous events in the Indian Ocean with relevance to
1997-1998", Journal of Geophysical Research , Vol. 105, No. C2
TRMM 3B43 includes
precipitation rate (mm/hr) and its root-mean-square (RMS) error estimates
derived from TRMM and other data sources. These gridded estimates are on a
calendar month temporal resolution and a 1-degree by 1-degree spatial
resolution global band extending from 40 degrees south to 40 degrees north
latitude.
The algorithm 3B-43 combines four independent precipitation fields:
monthly average unclipped TRMM Microwave Imager (TMI) estimate (intermediate
product from Algorithm 3B-42), the monthly average Special Sensor
Microwave/Imager (SSM/I) estimate (TRMM product 3A46), the pentad-average
adjusted merged-infrared (IR) estimate (TRMM product 3B42), and the monthly
accumulated Climate Assessment and Monitoring System (CAMS) or Global
Precipitation Climatology Centre (GPCC) rain gauge analysis (TRMM product 3A45).All input data sources are on the calendar month temporal resolution with the
exception of the adjusted merged-IR data which is on the pentad (5-day)
resolution. To obtain the requisite calendar month average of adjusted
merged-IR data, the algorithm 3B-43 averages the adjusted merged-IR pentads
that span the calendar month of interest. Also, prior to combination with the
SSM/I, adjusted merged-IR, and rain gauge data, the monthly average unclipped
TMI data is converted (re-calibrated) to TRMM Combined Instrument (TCI)
data using the TMI/TCI calibration parameters from Product 3B-31. After the
preprocessing is complete, the four independent precipitation fields are
merged together to form the final precipitation rate and RMS
precipitation-error estimates.
A complete description of Algorithm 3B-43 is provided in the
Algorithm 3B-43 User's Guide, available from the TRMM Science Data and
Information System (TSDIS). The file content description for Product 3B-43 is also available from TSDIS.
The data are stored in the Hierarchical Data Format (HDF), which includes
both core and product specific metadata, gridstructure, and precipitation rate
and relative error. The file size is about 0.2 MB (uncompressed). Sample
Fortran and C programs to read this data set are available at Hydrology
Online Information.
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Atmos Composition
![[rainfall of
TRMM 3B43]](images/trmm3b43.enso_000.gif)
![[SSTA longitude- time]](images/SSTA_98_99_000.gif)
