Forecasting atmospheric and oceanic circulations accurately over the Eastern Mediterranean has proved to be an exceptional challenge. The existence of fine-scale topographic variability (land/sea coverage) and seasonal dynamics variations can create strong spatial gradients in temperature, wind and other state variables, which numerical models may have difficulty capturing. The Hellenic Center for Marine Research (HCMR) is one of the main operational centers for wave forecasting in the eastern Mediterranean. Currently, HCMR's operational numerical weather/ocean prediction model is based on the coupled Eta/Princeton Ocean Model (POM). Since 1999, HCMR has also operated the POSEIDON floating buoys as a means of state-of-the-art, real-time observations of several oceanic and surface atmospheric variables. This study attempts a first assessment at improving both atmospheric and oceanic prediction by initializing a regional Numerical Weather Prediction (NWP) model with high-resolution sea surface temperatures (SST) from remotely sensed platforms in order to capture the small-scale characteristics

Anagnostou, Emmanouil N.

Case, Jonathan L.

Chronis, Themis

Haines, Stephanie L.

Mecikalski, John R.

Papadopoulos, Anastasios

NASA Technical Reports Server

I!
8.8 TOWARDS IMPROVED FORECASTS OF ATMOSPHERIC AND OCEANIC CIRCULATIONS
OVER THE COMPLEX TERRAIN OF THE EASTERN MEDITERRANEAN
Themls Chronls*_,Jonathan L Case2,
Anastas=osPapadopoulos3, Emmaneuil N. Anagnoetou4, John R Meclkalski_, and Stephanle L Haines5
_NASAMarshall Space FNghtCenter, Huntsville, AL
2ENSCOInc/Short term Pred_cbonResearch and Transition (SPORT)Center, Huntsville, AL
_Hellen=cCentre for Manna Research, Athens, Greece
4Unrvorsltyof Connecticut, Storrs, CT
_Umversltyof Alabama in Huntsville/SPoRT Center, Huntsville, AL
t. INTRODUCTION
Forecasting atmospheric and oceanic
circulations accurately over the Eastern
Mediterranean has proved to be an exceptional
challen_le The existence of fine-scale topographic
vanabllJty (land/sea coverage) and seasonal
dynamics vanations can create strong spatial
gradaents in temperature, wind end other state
variables, wh=chnumerical models may have ddt=culty
capturing
The Hellenic Center for Marine Research
(HCMR) is one of the main operational centers for
wave forecasbng in the eastern Mediterranean
Currently, HCMR s operational numencal
weather/ocean pred=ctlon model is based on the
coupled EtaJPrmeeten Ocean Model (POM) Since
1999, HOMR has also operated the POSEIDON
floabng buoys as a means of state-of-the-art, rea]-
time observations of several ocean=c and surface
atmospbenc vanables This study attempts a first
assessmem at =mprov=ng both atmospherLc and
oceanic prediction by inltlahzmg a regional Numerical
Weather Prediction (NWP) model w_thhigh-resoJut_on
sea surface temperatures (SST) from remotely
sensed platformsm order to capture the small-scale
charactenst_os
2. DESCRIPTION OF POSEIDON SYSTEM
QuaJityweather forecasting of the Mediterranean
Sea =s a distinct challenge as well as of utmost
_mportance More than 145 m=lhonpeop]e Lnhablthe
Mediterranean coast line and b{lhonsof tons of cargo
are transferred along sh=p trade routes, w=th the=r
number nsmg every year The complex coasthnes
and corresponding shadowing effects, coupled with
strong topographic and seasonal venations, make the
Mediterranean basra an excellent candidate for the
study of rigorous air-sea-land mleractlone
To address the observing and forecasting
challenges of the Mediterranean region, the HCMR
estabNshed the POSEIDON system, dedicated to the
operational mon=tonng and integrated fcrecasbng of
the manne environmental condit=ons of the eastern
Mediterranean basin and the Greek seas (NLttlset al
2001) The pnmary nblectlve of the POSEIDON
system Is to prowde real-t=me analys=s and
*Corresponding author address Dr Thernls ChronB, NASA
MarahatlSpace FlightCenter, 320 Sparkman Dr, HuntswIJe,
AL, 35805 Emall Th_mls,Ohronls-l@nasa gov
short-medium range forecasting for several
meteorological and oceanic variables over coastal
areas and open seas The POSEIDON system
currently consists of fwo ma_n components
observations and numencal modeling POSEIDON's
observat=onal part consists of 10 oceanographic
buoys (Figure 1) The mare phys=cal parameters
monitored consist of mean sea level pressure,
temperature, wind speed and direct=on,wave height
and direction (Figure 2), as well as water chem=stry
proxies such as eat_n_ly, d_seotved oxygen,
chlorophyll-A, etc
3, POSEIDON'S ATMOSPHERIC AND
OCEANIC FORECASTING
To sabsfy the forecasting requirements, a fully
operational coup(ed modehng system has been
developed consisting of meteorological deep and
shallow wave hydrodynamicsand sudace pollutant
diapers=on The POSEIDON weather forecasting sub-
system is based on the SKIRONIEta model and is
fully operational since September 1999, providing
daily 72-hour weather forecasts (Figure 3) The
SKIRON/Eta is an evolution of the 1997 version of the
NCEP/Eta (National Centers for Environmental
Pred=ctlons) model, developed at the University of
Athens (Papadopoules et aL 2002). POM is an
evolut=onfrom the re{hal numerical model designed by
Blumberg and Mel]or (1987). POSEIDON's POM
products include among others, predicted wave
height, direction and period (Rgure 4) The
eforemenboned _n 81tu buoy meteorological
o_servetlons are currently LJsedto assess the vehd_ty
of the weather forecasting model, whdelwave-he=ght
measurements are used to evaluate systemat=c
errors =n order to prowde adjustments to the wave
model
The POSEIDON operational NWP (SKIRON/Eta)
requires SST as bottom boundary cend=tions,which
in certain cases have an important impact on the
qualrty of the forecasts (eg fog format=on,
cyclogenesis, precipitat=on and air-sea flux
calculat=ons) POM provides a full 4-dimensional
desonptlon of the ocean at a variety off vertical and
horizontal spabal resolutions SST data are used as a
boundary cond=bonand in data &sSlmllatlon schemes
within these mode]rag systems For real-t=me
apphcat=cne, SST data must be accurate and
ava=[able=na t=melymanner from operationallyrobust
systems An important_ssueanses directly related to
the SST resolution used to imt=ahzeboth forecasting
https://ntrs.nasa.gov/search.jsp?R=20080013545 2019-08-30T04:06:26+00:00Z
models:theextensiveisland[andmaseesof the
Easternpartof theMediterraneanSealeadto
substantialheatcapacitydifferentialsndresu[tlng$STgradientsfromnear-shoretofewkilometersinto
theopenArchipelago.Moreover,air/seainteraction
phenomenasuchasEkmanupwellingdueto the
comp]excoastalorientation,or thermohaline
circulationinducedby the predominant wind direction,
can give rise to limited-area strong SSI differentials.
All the aforementioned regional characteristics can
cause unresolveable features in the analyses of
surface wind, temperature, and humidity, which can
subsequently lead to erroneous forecasts.
At present, the highest-resolution, continuous
and global SST products availab]o consist of the
1/12° Real-Time Global (RTG) product generated by
NCEP (Thi_baux et aL 20031. However, subjective
examination of these data by the authors suggest that
the product does not capture data at rasolutlons as
high as 1/12 °. The Met Office has recently deve]oped
a new Operational Sea Surface Temperature and
Sea Ice Analysts (OSTIA) system that provides global
products at 1/200-(~6 kin) resolution each day (Stark
et aL 2007). OSTIA has been designed to provide an
estimate based on a multi-scale optimal interpolation
(el) scheme which combines infrared and microwave
satellite and in situ SST measurements from ships,
buoys, etc. (Martin et aL 2006). Meanwhile, Haines et
aL (2007) have demonstrated the eapab[llty of
generating very high-resolutlon (1 km) SST
composites from the Earth Observing System Aqua
and Terra satellites for regional weather and
modeling applications.
This study seeks to take advantage of these
available datasets by aasim[[atlng these fields into a
high-resolution senfiguration of an NWP model, wLth
the ultimate goal of improving predictions of sensible
weather e[ements ever the Eastern Mediterranean.
4. PRELIMINARY EXPERIMENT
A first comparison is attempted between a
control run (CR) (i.e. SST originating from the R,G
product) and the experimental run (AR) (i.e. SST
originating from the OSTIA productl. The NWP model
used for these runs is the Weather Research and
Forecasting (WRF) model, using version 2.1.2 of the
Advanced Research WRF dynamical core
(Skamarock et aL 2005). A one-way nested
simulation was initialized at 0000 UTC 7 January
2008, with 12-kin hodzontal grid spaoing on the outer
domain, and 4-km horizontal grid spacing on the
inner domain centered on Greece and the Aegean
Sea. The nested run was integrated for 36 hours to
1200 UTC 8 January.
The ARW dynamioa] core is used with physics
options consisting of the rapid radiative transfer
model (M[awor et aL 1997) and the Dudhia scheme
(Dudhia 1989) for Iongwave and shortwaveradiation,
respectively. The WRF Single Moment 6-class
microphysics scheme (WSMS, Hang et aL 2004;
Skamaresk et aL 2005) is used in conjunctionwith
the modified Kain Fritash convectiveparameterizatian
scheme (Kain 2004) on the 12-kin domain only, and
without any convectiveparameterizationon the 4-km
inner nested grid. The planetary boundary layer and
turbulence processes are parameterized by the
Mellor-Yamada-Janii_ scheme (Janji_: 1990, 1996,
2002). The Noah land surface model (LSM, Ek et aL
2003) provides interactions between the land and
atmosphere. Surfaca-layar calculations of friction
velooities and exchange coefficients needed for
sensible and latent fluxes in the LSM are provided by
the NCEP Eta similarity theory scheme (Janjid 1996,
2002). Horizontal diffusion is handled by the two-
dimensional Smagorinskyfirst-order closure soheme
(Smagorinsky et aL 1965).
Figure 5 illustrates the SST of the CR (°C, upper
left), SST of the AR (°C, upper right) and their
respective difference (°C, AR-CR, bottom), all valid at
00Z (no forecasting is performed). AR-CR reveals
some kay observations:
• the 1-4 °C colder waters over the Bosporous
Straits (1),
the colder waters orlginating from the Ekman
upwel[ing layers across the eastern Aegean
Sea (2) and Thermaikos Gulf coasts (3),
• the colder waters from the Peloponnesian
gyre (4) and the associated thermohaline
(deep oceanic convection)
• the typically warmer waters of the Levantine
basin (5), overall one of the Mediterranean
areas with the highest SST recordings,
• the positive SST differences surroundingthe
Greek islands (6), depicting the heat
capacity gradients originating from the
tend/oceantransition.
Most of the aforementioned features are
translated into the sensible weather elements after
several hours of forecast (note the 30-h forecast 2-m
temperatures in Figure 6, valid at 0600 UTC 8
January). Both variables have a direct effect of the
forecast quality of other state variables such as
humidity, heat fluxes, and precipitation forecasting.
Figure 7 and Figure 8 show the 30-hour foreo_.st
sensible heat flux end simulated 1000-mb
frentogenasls (also valid at 0600 UTC ,8 January)
from the OR (upper left), the AR (upper right) and the
AR-CR (lower panel). The sensible heat flux
differences approach +_?.5-50W m-2,an amount that
is well beyond the measurement uncertainties
(Krahmann et aL 2000). Also, note the differences in
1000-rob frentogenesis axes over the Aegean Sea
and Mediterranean Sea northeast Of Crete,
correspond'ng o d'apacements in the ,predicted
• i I
convergence zones and shower act vty (not shown).
, , , i JThis sample s_mulatlon wth the hgherreseluton
OSTIA data clearly shows the sensitivity _fl the NWP
solution and the importance of resolvng _fne-scale
SST structurein the Aegean Sea region.
5. SUMMARY
This paper dasoribed ways of improving the
HCMR's POSEIDON forecasting capabilities.
Forecasting over the eastern Mediterranean basin,
due to its partioular physiography, is particularly
sensitive to smal!-scale variations in SST. WRF
forecastsbasedon SSTproductsof different
resolutionwere presented and shown to be sensitive
to the static SST fields used in the simulations.
Further test-oases combined with regional ground
and satellite validation is required to underline the
overall forecast improvement. Ongoing efforts in
assimilating surface and satelhte-retrieved winds, soil
moisture, humidity, and atmospheric temperature
profiles, focused over the eastern Mediterranean
basin will fuither enhance the POSEIDON's
meteorological and oceanic forecasting skills,
6. ACKNOWLEDGEMENTS/DISCLAIMER
The European Free Trade Association (EFTA)
and the Greek Ministry of National Economy have
funded the POSEIDON system. Mention of a
copyrighted, trademarked or proprietary product,
service, or document does not constitute
endorsement thereof by the authors, the National
Aeronautics and Space Administration, the Hellenic
Center for Manne Research, ENSCO Inc., or the
United States Government. Any such mention is
solely for the purpose of fully informing the reader of
the resources used to conduct the work reported
heroin,
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Figure 1. Locations of the 10 POSEIDON oceanic buoys.
Figure 2. Sample plot of significant and maximum wave height (m) at the POSEIDON
Mykonos buoy.
Figure 3. Sample numerical forecast of 1O-m winds from the coupled atmospheric/oceanic
SKIRON/Eta model.
Figure 4. Sample prediction of significant wave height and direction from the Princeton
Ocean Model as run at HCMR.
RTG SST (C) valid 080107/0000VDOO OSTIA SST (C) valid 080 107/0000VDOO
SST Diff (OSTIA. RTG) valid 080107/0000VOOO
Figure 5. Initial SST fields at 0000 UTC 7 January 2008 for the Control Run (Le. RTG, upper-left),
Experimental Run (OSTIA, upper-right), and difference field (OSTIA-RTG, bottom panel). Major geographical
features referred to in the text include (1) Bosporous Straits, (2) eastern Aegean Sea, (3) Thermaikos Gulf
Coast, (4) Peloponnesian gyre, (5) Levantine basin, and (6) Greek islands.
RTG 2·m Temperature (C) valid OSOlOS/0600V030 OSTIA 2·m Tempel'ature valid OSOlOS/0600V030
4
2
o
B
6
4
2
o
2
4
2
o
B
6
4
2
a
2
2·m Temp Diff (OSTIA. RTG) valid OSOlOS/0600V030
Figure 6. WRF simulated 2-m temperatures at the 30-hour forecast valid 0600 UTC 8 January for the
Control Run (upper-left), OSTIA run (upper-right), and difference fields (OSTIA-RTG, bottom).
RTG Qh (W 1ll"''''.2) valid OSOlOS/0600V030
00 00
00 00
00 00
00 00
a a
5 5
a 0
5 5
10 10
25 25
50 50
100 100
OSTIA Qhvalid OSOlOS/0600V030
Sensible HF Diff (OSTIA· RTG) valid 080108t0600V030
Figure 7. WRF simulated sensible heat flux at the 3D-hour forecast valid 0600 UTC 8 January for the
Control Run (upper-left), OSTIA run (upper-right), and difference fields (OSTIA-RTG, bottom).
lO00-mb Frontogen_ds (10100km/3hr)_[li.d 080108/@600V030
_0
_5
10
n_
(coler=OSTIA; gray=CO N)
Figure 8. W RF simulated 1000-mb frontogenesis and 10-m wind vectorsat the 30-
hour forecast vafid 0600 UTC 8 January for the Control F_un(gray shading), and
OSTIA run (color shading, accordingto scale provided).


Towards Improved Forecasts of Atmospheric and Oceanic Circulations over the Complex Terrain of the Eastern Mediterranean

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