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OCR for page 13
Implementation Plan, ought to assume a broader role, as a Central
Processing and Assessment Facility for Water Vapor Data and
Analyses, by actively ensuring that the goals cited above are achieved.
Within the currently planned structure, GVaP should explicitly
involve centers that collect and compare special, high-quality, high-
resolution water vapor measurements with the measurements made by
various global observing systems. Especially important, too, is the need
to involve operational weather centers in GVaP, which will not only
benefit the creation of a merged product, but, conversely, will also
expose the operational centers to ongoing developments in the
measurements. One of the more tangible benefits of the GEWEX
Continental-Scale International Project (GCIP) has been the im-
provement of the National Centers for Environmental Prediction
(NCEP) operational weather analysis system using results obtained
from the measurement campaigns (NRC, ] 998~. The pane! believes that
the operational centers would accrue similar benefits were they to be
linked to GVaP through the Central Facility. This goal could be
accomplished by including an Operational Weather Analyses and Data
Center on equal footing with the other Centers in the Implementation
Plan's Data Development Procedure. The outputs from such a Center
could, for instance, be effectively used to inform the process of
defining the vertical structure needed for computing water vapor fluxes.
As noted in the draft Implementation Plan (IGPO, 199Sb), models
for structuring GVaP already exist in both the International Satellite
Cloud Climatology Project and the Global Precipitation Climatology
Project. There is every reason to believe that a GVaP similarly
organized around a scientifically strong, active Central Facility will
also be successful. Like these two projects, one of the greatest benefits
of GVaP will be the creation of carefully synthesized water vapor data
sets to serve the research community.
U.S. Opportunities
To understand the role of water vapor in the climate system, a
comprehensive and ambitious program is required, as recognized by the
GVaP Science and Implementation Plans. GVaP could make major
13
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contributions to this effort by focusing on the data collection,
processing, and analysis tasks, in a fashion similar to that of other
GEWEX Radiation Projects. In making these contributions, GVaP
must maintain close ties to the relevant research communities to ensure
that its products are being developed with maximum utility. A U.S.
national research program would benefit considerably from a
foundation grounded thusly on quality-controlled, comprehensive data
sets.
To realize the key contributions noted above, the panel
recommends that U.S. agencies consider targeting support for one or
more of the individual Data Centers and/or the Central Facility, as
appropriate. For example, NCEP, the only civilian operational
meteorological center in the nation, might be selected by the federal
agencies to host a center focused on the utilization of operational
products related to water vapor. Competitive proposals and bids for
operating any of these organizations will help ensure that the best
possible expertise is brought to bear on the challenge of measuring and
analyzing water vapor. The pane! wishes to emphasize, however, that in
no way should such support, including that for a scientifically strong
and active Central Facility, be regarded as a substitute for maintaining a
vigorous, well-funded extramural research community. Agency support
for research outside the GVaP data development structure needs to be
part of an overall GVaP effort, and the activities of individual
investigators need to be properly considered by GVaP.
The first step in advancing understanding of water vapor and its
role in the climate system is to obtain an accurate quantitative
description of the variations of water vapor in space and time; several
global data sets already exist, but, as alluded to at the outset, their
quality is less than desirable. The U.S. program can leverage its limited
resources to accomplish this step most effectively by participating in
the international GVaP project. Contributions that the United States
should make in addition to its current activities such as remote
sensing include the following: (a) improve instruments, analysis
techniques, and sampling strategies to make better water vapor
measurements, with special emphasis on efforts to increase vertical and
temporal resolution and to improve accuracy in the upper troposphere-
lower stratosphere region; (b) implement use of reference radiosondes
to facilitate the ongoing calibration of different moisture sensors; (c)
provide critical, high quality data sets from the U.S. DOE ARM
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program sites and WVSS to validate satellite remote sensing results; (~)
lead the effort to compare and evaluate available and new data sets; and
(e) undertake a new synthesis of existing and new sources of
information about water vapor to produce a global water vapor data set
with the needed improvements in accuracy.
Although the above are necessary first steps, it is essential that a
U.S. GVaP effort recognize the importance of combining water vapor
observations with other data to understand the complete water
exchange process. For example, a close association between GVaP and
the GEWEX Cloud System Study will help advance understanding of
cloud-water vapor interactions. In addition, effort should be made to
collect improved and more detailed water vapor measurements as part
of the GEWEX America Prediction Project. A goal of U.S. hydrologic
research programs should be to quantify the rates of evaporation from
the land and ocean surface, the rates of water transport by large-scale
atmospheric motions, and the rates of conversion of water vapor into
clouds and precipitation. Thus, the products of the GVaP program must
be capable of being integrated with other analyses of evaporation,
clouds, precipitation, convection, and winds, over Earth's entire
surface. For instance, improvements in wind observing capabilities,
particularly in the lower troposphere, will be required if water vapor
transport is to be accurately estimated. It is therefore necessary that the
development of new data products within GVaP be undertaken with an
awareness of how the data will be used (e.g., for analysis and modeling
estimates of large-scale transport, radiative effects, energy cycling) to
ensure that the research objectives of the scientific community are met.
15
Representative terms from entire chapter:
vapor measurements
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