SOWER Introduction
SOWER/Pacific
The Soundings of Ozone and Water in the Equatorial Region/Pacific
Mission (SOWER/ Pacific) has been running on a campaign basis since
1998 to improve our knowledge on the ozone and water vapor
distributions in the tropical Pacific region by making coordinated
radiosonde observations at three equatorial places, the Galapagos
Islands (Ecuador), Christmas Island (Kiribati), and Indonesia.
In addition to establishing the climatology and variabilities in
ozone and water vapor, we also intend to explore controlling
dynamical/chemical processes for these species and to collect
correlative data for satellite data validation.
Scientific issues
Total ozone variations in the equatorial region are characterized
by the annual cycle, Quasi-Biennial Oscillation (QBO), and those
related to El Nino/Southern Oscillation (ENSO).
The annual maxima take place around August-September period,
while the minima are observed in the northern winter.
The zonal structure is known to show a persistent wave-one pattern
with the minimum located around the date line.
The QBO in ozone is characterized by zonally uniform variations,
while the ENSO component has both zonally symmetric and zonal wave
components.
Due to lack of observational data, however, the contribution of
the tropospheric ozone to these features and ozone variations
around the tropopause have not been well described yet,
making it hard to understand even the fundamental processes
responsible for those variations.
Water vapor distributions in the tropical upper troposphere (UT)
and lower stratosphere (LS) are of crucial importance for two reasons.
Water vapor in UT is a main emitter of the Earth's infrared radiation,
controlling the Earth's radiative balance.
Thus, the so-called water vapor feedback, including the role of
clouds, associated with the man-induced global warming is one of
the most important current scientific issues.
The other point is the water vapor transport processes from UT to LS
in the tropics, which is known to greatly affect the stratospheric
ozone photochemistry and the recovery of the higher-latitude
stratospheric ozone depletion.
However, again, due to the lack of observational data, even the
distribution of water vapor in the UT/LS region has not been
well characterized yet.
Tropical Pacific is characterized by east-west contrast both in
dynamical and chemical point of view.
Prevailing easterly wind near the surface brings about a marked
contrast in the sea surface temperature (SST) distributions along
the equator.
In the western Pacific (Indonesia to Tarawa) where SST is high,
much moisture from the warm seas and the efficient solar heating
on the islands together make the region one of the most active
convective regions in the world. Vigorous convections there
sometimes transport near surface airmasses up to the tropopause
region, the highest and coldest tropopause in the world.
On the islands they maintain the rich biomass which may result in
emitting various chemical species related to the tropospheric
ozone photochemistry.
In the eastern Pacific (the Galapagos) where the cold upwelling
results in low SST, the atmosphere is not highly convective but rich
in layering structures, and the large (and warm) outgoing
longwave radiation from this region plays a crucial role in the
Earth's radiative balance. The cold upwelling also causes rich
biological activity, which may affect the photochemistry in the
marine boundary layer in this region.
The above east-west pattern is sometimes greatly disturbed in
association with ENSO, and the central Pacific (Christmas Island)
could have both characteristics depending on the phase of ENSO
and would be the most sensitive region to the climatic variability.
Observation bases and previous campaigns
Figure 1 shows the current SOWER/Pacific bases in the tropical
Pacific, (1) Watukosek (and some other places), Republic of Indonesia
in the western Pacific, (2) Christmas Island, Republic of Kiribati
in the central Pacific, and (3) the Galapagos Islands, Republic of
Ecuador in the eastern Pacific.
Figure 1. SOWER/Pacific bases.
For the ozone measurement, we use the meteorological balloon-borne
electrochemical concentration cell (ECC) ozonesondes.
For the water vapor measurement, we use four different balloon-borne
sensors (often at the same time), i.e.,
(i) the relative humidity sensor of the meteorological radiosonde,
(ii) a Swiss-made commercial chilled-mirror hygrometer
named "Snow White,"
(iii) a US-made cryogenic chilled-mirror hygrometer developed at
National Oceanic and Atmospheric Administration (NOAA), and
(iv) another US-made cryogenic chilled-mirror hygrometer
CU-CFH developed at University of Colorado.
Previous observational campaigns are summarized here.
[The Galapagos Islands]
March-April 1998; August-September 1998; February-March 1999;
September 1999; March 2000; September 2000; November-December 2000;
September 2001; March 2003; July 2004.
[Christmas Island]
February-March 1999; September 1999; March 2000; November-December 2000;
November-December 2001; June 2002; August 2002; October-November 2002;
January 2003.
[Tarawa]
December 2003; December 2004; January 2006; January 2007.
[Indonesia]
September 2000; November-December 2000; July 2001; November-December 2001;
January 2003; December 2003; December 2004; January 2006; January 2007.
[Hanoi]
September 2004; December 2004-January 2005; January 2006; January 2007.
In September-October 1999, we made a ship cruise from Hawaii to
Mexico through the equatorial eastern Pacific (between Christmas
Island and the Galapagos) onboard R/V Shoyomaru
(Japan Fisheries Agency).
In December 2004-January 2005, we made another ship campaign
near Palau onboard R/V Mirai (JAMSTEC).
We have made the "Match" type coordinated soundings in the
tropical western Pacific in December 2004, January 2006,
and January 2007.
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