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OCR for page 10
international GVaP is to be commended for recognizing this need and
for attempting to bring together the diverse measurement and research
communities under a single project devoted to water vapor. The pane'
believes that one of GVaP's most enduring legacies may indeed lie in
the communication it can establish among the measurement, analysis,
and research communities.
Comments on the
Science and Implementation Plans
The overarching goal, approach, and research objectives listed in
the draft Science Plan (IGPO, 199Sa) are at once meritorious and
extremely ambitious. The GEWEX Pane] believes that some aspects of
the proposed program, especially those positioning GVaP as an
interface between data providers and users, are more tractable than
others. In particular, attempts to deal with cloud-scale processes will be
especially difficult given the resolution of the observing systems
discussed in the GVaP Implementation Plan. Nevertheless, the
microphysics of hydrometeors for example, their re-evaporation in
the tropical upper troposphere is critical for understanding water
vapor-radiation feedbacks. In this connection, however, GVaP can be
especially valuable to the modeling community by synthesizing the
larger-scale measurements that are an important component of de-
veloping improved parameterizations within global models.
Moving forward with its plans, GVaP should pay particular at-
tention to the following activities:
Gather, assess, and distribute existing water vapor data sets and
products.
The proposed effort to gather all relevant water vapor data sets
should include careful attention to incorporating metadata so that
updated versions of data sets can be properly identified and linked
to previous versions. Other documentation, such as error estimates,
also will be critical to future reprocessing efforts. Because of the
large number of existing and planned data sets, a primary initial
objective should be to assess their quality so that users are made
10
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aware of the strengths and limitations of each observational
product, including its utility in documenting long-term trends. This
will also enable the measurement community to define the
performance characteristics of prospective observing systems to
resolve these deficiencies.
.
.
Coordinate data set intercalibratior' arid comparison with results
from validation experiments.
The GVaP project should take specific responsibility to examine
and understand the systematic differences between available water
vapor data sets and those resulting from its own analyses. This
effort would be the first step in developing and applying new,
consistent calibrations to water vapor data. The pane! recommends
that the development and implementation of a reference radiosonde
be a high priority. Given the crucial importance to climate research
of detecting long-term trends in tropospheric water vapor and the
limited lifetime of GVaP, the implementation of a reference radio-
sonde is important to ensure the ongoing calibration of different
moisture sensors.
Highlight upper tropospheric water vapor.
Upper level water vapor feedbacks are a major source of
uncertainty in global warming simulations. The proposed GVaP
focus on global upper tropospheric water vapor could yield
especially large benefits in addressing this issue, given the known
strengths and weaknesses of the principal data sets to be
-assimilated. Because of the growing collection of existing, and
often conflicting, measurements for this region, GVaP needs to
give additional thought to how it can best contribute to this subject.
Close collaboration with the work of the SPARC program should
be established, in particular with SPARC's work to better
understand upper troposphere-stratosphere interactions.
· Create new water vapor products, including a merged global water
vapor product.
The emphasis here should be on a hierarchy of products, including,
for example, higher resolution regional products and global
products of different space-time resolutions. The pane! recognizes
that for many users, however, a single merged, "final" product
11
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would be most useful and should be generated. The pane! strongly
recommends that access to the base data used to derive a merged
product be maintained, in light of the diverse applications of such
data for which properties of "optimal" analyses may differ
substantially. The techniques to be employed for a merged product
should be drawn from the mathematical tools associated with data
assimilation in support of numerical weather prediction. In
applying data assimilation approaches to create water vapor
products, the direct input of radiances may be preferable to the
input of retrievals. Quantification of uncertainties, including bias
and error covariance properties, should accompany the creation of
any new water vapor data products intended for broad use.
.
Foster broad community involvement and sponsor workshops.
End users of GVaP products must have mechanisms for providing
feedback about the quality of these products. The free and open
international exchange of GVaP data and products must be
supported in order for the measurement, analysis, and modeling
communities to be properly engaged. It is especially important for
GVaP to engage those responsible for maintaining operational,
global climate observing capabilities so that the advances of GVaP
can extend beyond its proposed lifetime. GVaP should also involve
those responsible for developing new measurement capabilities by
documenting and prioritizing deficiencies in current data bases so
that performance characteristics of new observing systems
(including sampling strategies and optimal mixes of measurements
and models) can be designed to remedy the most important
problems. Furthermore, in addition to the focused workshops
described in the draft Implementation Plan, GVaP ought to help
sponsor more broadly based conferences organized by others
interested in water vapor-related issues. Community interaction
might also be facilitated through the effective use of Web-based
tools.
To accomplish the goals discussed above, the Data Development
activities described in sections 2.2.4 and 2.2.5 of the draft Imple-
mentation Plan provide a structure that can deliver meaningful and
necessary products to users. The panel believes that the heart of this
structure, the Global Processing Center envisioned in the draft
12
Representative terms from entire chapter:
vapor data
