[Comments from CLIVAR AIP on the PIRATA Status and Perspectives
Document]{.underline}

**1. Introduction**

At the PIRATA X (Fortaleza 2004) and PIRATA XI meeting (Toulouse 2005),
Brazilian, US and French partners in the PIRATA program expressed their
desire to extend the program, but decided that an assessment should take
place by CLIVAR and GOOS. Members of the Atlantic Implementation Panel
of CLIVAR and the Ocean Observations Panel for Climate of GOOS performed
the review based on the document "PIRATA; accomplishments of PIRATA :
1997-2005. Status and Perspectives".

In general CLIVAR strongly supports the PIRATA program. According to
CLIVAR it is of the foremost importance to maintain the current mooring
array and to strongly support the currently planned extensions. This
would enable PIRATA to be firmly established as the main backbone of the
tropical Atlantic observing system. The failure to do so would be a
disaster for climate science community. The new Northeast, Southwest and
Southeast extensions of the mooring array are strongly supported.
Concerns rise as well. Some of these are of practical nature, in
particular the issue of vessel support and vandalism. To guarantee a
sustained observing system these should be addressed. Also, some of the
goals of PIRATA are broad and one should be cautious about predicting a
quick, large and positive impact of PIRATA data on the results coming
out of (seasonal) prediction systems and ocean state estimation. There
is a need for an integrated framework in order to see how all the
different actions (in situ, modelling, data assimilation, satellite
observations, etc) interact constructively with each other. This would
be important in terms of setting priorities for new actions to be
launched in the future.

CLIVAR would like to commend the participants of this project for their
perseverance in the face of numerous adversities to obtain a major
improvement in the description of the conditions in the tropical
Atlantic region.

On behalf of the CLIVAR Atlantic Implementation Panel,

Wilco Hazeleger

**2. General remarks**

The *Pilot Research Moored Array in the Tropical Atlantic* (PIRATA)
review document is well written and very concisely summarizes the status
and accomplishments of the various PIRATA teams.

The goals of the PIRATA project extend from description through
understanding to prediction of variability in the coupled
ocean-atmosphere system in the Tropical Atlantic, and by implication to
improved understanding and predictability in the regions influenced by
the tropical Atlantic. These are clearly very broad and challenging
goals, particularly given the shortage of technical and research
capacity initially available in the region.

PIRATA is largely motivated by the expected societal benefits to be
derived from an improved ability to predict ocean conditions and
ocean-atmosphere exchanges in this region and the influences on weather
and climate -- for both the ocean and the atmosphere. Major effects
include variability in fisheries, winds, precipitation and air
temperatures. There is also a need for improved understanding of the
horizontal and vertical ocean circulations in the equatorial band, the
associated cross-equator transports of heat and how these might be
influenced by local or remote variability.

To address the above challenges, the first step was (and continues to
be) to develop an improved description of basic conditions and the
variability in these conditions. Thus a major sustained field program in
this region was clearly essential. Fulfilling this objective has been
complicated by limited financing and the lack of adequate local vessel
and technical support, and the situation has been exacerbated by
additional challenges including unexpected interruptions in vessel
availability and costly vandalism, presumably by some of the people that
the project aims to benefit.

The PIRATA project has wisely built on the expertise and technical
developments previously established for the TAO array in the equatorial
Pacific and it has benefited from additional technical developments
during its lifetime. Noteworthy are improved satellite measurements of
sea level, SST, rainfall and winds, improved rain and salinity
measurements from the ATLAS buoys, and improved information on the
larger scale variability in upper ocean conditions supplied by the Argo
project. Tide gauge, air pressure, SST and SSS data from São Tomé and
new meteorological stations at Fernando de Noronha Island and St. Peter
& St. Paul Rocks also contribute to the near-real-time data that is now
available and all of this information can now be ingested into
operational modelling systems that have developed very significantly
since the initiation of PIRATA.

In addition to the rapid-access information mentioned above, a suite of
measurements (ADCP, surface temperature and salinity, CTDs, XBTs,
meteorological observations etc.) are made during each servicing of the
PIRATA observation network and continuous ADCP measurements are
available over the upper 130m since late 2001 from a mooring located at
23°W-0°N, coincident with an ATLAS buoy site. All of these observations
have greatly increased the baseline information available for the
region.

Finally, it is clear that the PIRATA field program has and will continue
to form the foundation for some programs and to complement others;
noteworthy examples include Argo, AMMA (African Monsoon
Multidisciplinary Analyses), TACE (Tropical Atlantic Climate Experiment
-- endorsed), BCLME (Benguela Current Large Marine Ecosystem), GOOS
(Global Ocean Observation System), SOLAS (Surface Ocean -- Lower
Atmosphere Study), GODAE (Global Ocean Data Assimilation Experiment) and
CLIVAR (Climate Variability and Predictability). The importance of this
"foundation role" in an area where data coverage is sparse and field
programs are particularly challenging to mount should not be
underestimated.

**3. Achievements**

It is clearly demonstrated that the PIRATA array has provided an
invaluable amount of data for numerous and varied applications, among
which one can cite for instance, analysis of climate variability at
seasonal-to-interannual timescales, equatorial dynamics, mixed-layer
temperature and salinity budgets, air-sea fluxes, data assimilation,
weather and climate forecasts etc ... It is of the foremost importance
to maintain the current mooring array and to strongly support the
currently planned extensions. This would enable PIRATA to be firmly
established as the main backbone of the tropical Atlantic observing
system. The failure to do so would be a disaster for climate science
community. The CLIVAR science community desperately needs long and
coherent datasets to study interannual to decadal fluctuations and their
interaction with anthropogenic climate change.

It is clear that the basic goal of improved description of oceanic
conditions and air-sea exchange (including variability in these
conditions) has been achieved by PIRATA and the policy of making
observations freely and rapidly available via the internet has gone a
long way towards optimizing the use of this information. Capacity
building is an additional aspect of the observational program that
should not be overlooked, particularly given the well-known inadequacies
of observations in the southern hemisphere, and the relatively poor
funding in the region. Hopefully, the increased technical and research
capacity developed through projects like PIRATA will eventually help
reduce the imbalance between observational programs north and south of
the equator. Overall, the participants in this project are to be
commended for their perseverance in the face of numerous adversities to
obtain a major improvement in the description of the conditions in this
region.

Given that the field program goals of PIRATA have been (and continue to
be) successful, we must ask if the additional information collected is
being put to good use. The publications listed in the status and
perspectives document make it clear that the data have been used to
address numerous descriptive and technical issues, including the
provision of improved descriptions of seasonal and interannual
variability in ocean conditions and air-sea fluxes and the
reliability/uncertainty of the information that has been collected both
by the PIRATA array and from satellites. Further, the goal of using
budget calculations to help determine the relative roles of surface
fluxes and oceanic processes in the determination of surface and
upper-ocean variability has been realized to the extent possible. In
addition, many other technical issues and descriptive works have been
successfully addressed. It is clear that the data collected is of high
quality, but it remains somewhat sparse -- a fact that is, at least to
some extent, being addressed by recent and proposed extensions. However,
PIRATA seems to focus on seasonal and interannual time scales.
Intraseasonal variability is also of importance in the region. In
addition to seasonal outlooks, meteorological agencies in the region (eg
the South African Weather Service) are also concerned with extended
range forecasts, particularly for agricultural applications.

To justify the transition of PIRATA from a pilot project to a sustained
operational observing system providing real-time information for use in
weather and climate prediction, definitive evidence of economic value is
essential. The demonstration of such value will inevitably require
predictive models with useful skill. An important issue is whether or
not strong evidence of net economic value will be available by the end
of the present consolidation phase. In this regard, the recent and
proposed extensions are encouraging since they increase the potential
for skillful predictions of events like the Benguela Niño and its
effects on local rainfall. This type of predictive work seems essential
to justify the transition to a long-term observing system with secure
funding commitments, but has not been planned in a coordinated way (the
TACE project is a first step toward this goal).

Also important are projects like TACE and AMMA that will make use of
PIRATA data and build on the PIRATA backbone to address clearly
complementary goals. The resulting prospects for improved understanding
of dynamical processes and applications to the development of predictive
systems certainly increase the prospects for successful transition to a
sustained operational system. In particular, it is clear that to improve
forecast capabilities over any/all timescales, observations must be used
to improve model initializations and to constrain and/or validate model
variability. With the baseline data provided by PIRATA and other
programs (including satellite observations, Argo data and meteorological
observations) this is now possible and is being put into practice.

A great deal of work has been achieved on validation of existing remote
sensing data, in particular satellite SST products, with some very
interesting new results (among others the overestimation of the latent
heat flux by reanalysis products and the thorough validation of the
EUMETSAT OSISAF data products). All these activities are strongly
supported by CLIVAR.

This being said, a complete, detailed and coherent assessment of the
scientific potential of the PIRATA array is a delicate and complex task.
It is not obvious and sometimes impossible to objectively assess the
real impact of PIRATA data for some of the objectives, just because the
number of years is still limited and/or due to non homogeneity in the
observing system (for instance, it may not be realistic to study the
impact of assimilating PIRATA data on the quality of seasonal forecasts
in the tropical Atlantic region, this would require a much larger
dataset -10 years is barely enough - in terms of temporal coverage). In
terms of the main goals (stated page 6), it is probably fair to say that
the first two have been quite successful while the third one is a little
bit behind. The third goal is "to provide a set of data that could be
used to develop and improve the predictive models of the
ocean-atmosphere system". This covers both the estimation of the initial
ocean state to be used for the prediction and the coupled models used to
perform the forecast. These are obviously long-term goals and the role
of PIRATA data is certainly important, but many other factors are
probably as or even more important. Thus, one should be cautious in
predicting a quick, large and positive impact of PIRATA data on the
results coming out of the prediction systems. This is likely going to be
a very long and difficult task with an unknown outcome at this time. The
last point is the position of PIRATA with regard to other current or
planned initiatives. There is a strong need to better define the global
picture which encompass all these projects. This suggests the need for
an integrated framework to be developed in order to see how all the
different actions interact constructively with each other. This would
also be important in terms of setting priorities for new actions to be
launched in the near future.

**4. Recommendations and comments**

**4.1 General**

Based on the fact that high-quality data is being successfully collected
and used in both research and operational projects, and the fact that
each of these applications shows great promise to grow and complement
the other, we recommend that the PIRATA project be continued and
transitioned to a long-term system to the extent possible. However,
several issues need to be carefully addressed to ensure that the project
is cost-effective and hence sustainable. Some specific considerations
and concerns include:

1.  The most obvious issue that needs to be addressed is vessel support.
    It is clear from Appendix 8 of the Status and Perspectives document
    that this issue has been carefully considered and it appears that
    the status quo may become the option of choice more because of
    inertia than for good scientific or logistical reasons. We encourage
    the PIRATA Resources Board to continue to push this issue to find a
    more permanent and reliable solution. Any such solution should
    attempt to take into account the need for additional observations,
    particularly to the south, in addition to the PIRATA program.

2.  The ongoing efforts to reduce the losses associated with vandalism
    must obviously be continued.

3.  We support continued efforts to extend the PIRATA array in
    scientifically justified and cost effective ways. The proposed SW
    extension off Brazil, the SE extension off Angola and the NE
    extension along 23°W are each well-justified in the report and
    warrant support to the extent possible. However, it should be noted
    that the SE extension is a pilot project supported by BCLME (Angola,
    Namibia, South Africa) and not by South Africa as the PIRATA
    document states. The mooring has been deployed near 6S, 8E in June
    2006 during an EGEE cruise. Also, Benguela Nino's influences
    rainfall over western Angola and northwestern Nambia, but there is
    not much evidence as yet for a broader impact.

4.  CLIVAR supports the complete instrumentation of the PIRATA fluxes
    reference sites. This is crucial if one wants to go further in the
    understanding of coupled air-sea processes at various time scales.

5.  Although one of the main objectives of PIRATA was to monitor the
    equatorial and meridional modes, it is unclear whether the actual
    network is optimally calibrated to assess the fluctuations of these
    modes. Figure 7 shows that there are instances where the simple
    index derived from PIRATA is not in good agreement with the usual
    SST dipole index (1999 and 2001). The diagnostic provided to show
    the lag-relationship between the two modes isn't very clear (figure
    9). A more detailed assessment of the capability of the current
    network to depict the links between the two modes is certainly
    required. In this regard, the proposed extensions to PIRATA would
    certainly be very useful. Also, a higher resolution near the equator
    is required to resolve the waveguide. CLIVARs WGSIP has indicated
    that a denser network is needed to make progress in seasonal
    forecasting. Another interesting question is the frequency
    dependence (and in particular at sub-annual time scale) of this
    relationship, which can certainly be examined with PIRATA data.

6.  In terms of longer plans, it is striking to see that the document
    focus on the meridional resolution of the equatorial waveguide and
    the Gulf of Guinea region only while the region of the north Brazil
    current is not mentioned, contrasting with the strong statement made
    on page 39. This is a bit surprising as this region has a strong
    influence on western tropical Atlantic SST anomalies which are very
    important in terms of tropical-extra tropical teleconnections.

7.  Finally, there are obvious questions and concerns about whether or
    not the full (extended) PIRATA array can be maintained in a
    long-term program. A careful determination of the most critical
    elements of the array is clearly needed in case program cuts are
    required. Such an evaluation should consider the consequences for
    funding, R&D and operational programs if specific elements of the
    array are eliminated. This evaluation needs to take into account
    other data sets (e.g., observations from satellite platforms and
    Argo) that may help fill the gaps.

**4.2 Links with the modelling and synthesis community.**

The use of PIRATA data in operational ocean and atmospheric modeling is
very encouraging. The development of coupled data-assimilative
ocean-atmosphere models is a challenging area of research that needs to
be supported if maximum long-term benefits to society are to be
achieved. This is particularly true for medium to long range weather
forecasting where the evolution of ocean conditions are important and
are unlikely to be well-represented by persisted ocean anomalies. CLIVAR
encourages more work in this area and particularly:

1.  PIRATA data could be used more in terms of validation of existing
    coupled models. Most coupled models have 0-order biases in their
    representation of the basic features of the tropical Atlantic
    climatology. The current PIRATA data could be used to better
    understand why the coupled models have such large biases in terms of
    the zonal SST gradient mean state (it is indeed a coupled problem
    and has to be analyzed as such). The use of PIRATA fluxes to
    validate coupled climate models in terms of the SST-heatflux (both
    radiative and turbulent components) feedback is strongly encouraged
    even though one has to devise a clever way to compare in situ data
    with model gridded data. This is essential as it will provide an
    indication of the persistence of the SST anomalies which is likely
    to play an important role in terms of potential predictability. It
    is useless (in terms of improving predictability) to have the best
    array of moorings as well as the best data assimilation system if
    the initial state ocean (sub-)surface anomalies are unrealistically
    washed away by the coupled models used in climate forecasts. It is
    encouraged that the PIRATA community liaises well with WGOMD and
    WGSIP panels of CLIVAR and WCRP to improve this.

2.  Tuning of high resolution ocean models through their representation
    of the EUC (Clipper and MOM simulations) as well as process studies
    such as the role of TIWs upon the transport of the EUC, the
    behaviour of the EUC in the Gulf of Guinea. This is clearly a very
    important topic as it has very important consequences in terms of a
    better understanding of the equatorial dynamics in the Atlantic and
    improvement of ocean physical parameterizations. These types of
    studies should be strongly encouraged in the future (for instance
    the importance of the diurnal cycle on the representation of coupled
    processes and the links with the vertical resolution needed in ocean
    models). Again, liaising with the modelling panels is encouraged.

3.  Ocean state estimation: much more work is needed to really prove the
    positive impact of PIRATA data upon the ocean state estimation.
    Comparison of simulations with and without PIRATA data assimilation
    has to be performed with independent data and for longer periods.
    Reasons for the not-so-large improvement when using PIRATA data
    should be better understood although it seems probable that it
    partly lies in the data assimilation technique that is currently
    used in the MERCATOR prototype (it is hoped that MERCATOR will
    slowly evolve towards variational techniques which have proved to
    outperform OI schemes in the tropical Pacific).

**4.3** **Links with other programs**

Supplementing the backbone PIRATA observations with additional research
projects such as TACE and AMMA is also encouraged. Strong links exist
between PIRATA and the Atlantic Implementation Panel of CLIVAR. Similar
interaction with the Working Group on Seasonal and Interannual
Prediction (CLIVAR-WGSIP) and Working Group on Ocean Model Development
(WGOMD) is encouraged. These types of R&D projects are essential to
maximize the benefit from the investments made in the PIRATA program. In
addition, PIRATA is relevant to the biogeochemical cycles and ecosystems
research communities (e.g. impact on low oxygen zones and fisheries).
Specific comments:

1.  The links seem obvious but are not sufficiently detailed in the
    document. In particular, the scientific links with AMMA are
    considered as obvious, however this is not the case since AMMA is
    mostly concerned with the hydrological cycle over the continents.
    The same could be said with regard to TACE.

2.  More generally, there is a need to better define the roadmap to
    optimally link on one hand very detailed process studies and the
    observations network, and on the other hand the more global and
    integrated climate picture.