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Water and energy budget over the
Mediterranean Sea,
East-West differences
(M-Atlas)
AOSC 658N
Martina Ricko
Dec 5, 2007
Introduction:
Many studies have been focused over the Mediterranean area:
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Present and past precipitation and temperature variability, large scale dynamics and trends in the
Mediterranean (Xoplaki, et al 2004),
-- Mediterranean summer air temperature variability and its connection to the large scale atmospheric
circulation and SSTs (Xoplaki, et al 2003)
Mediterranean climate variability (Lionello, et al 2006)
The energy and water budgets of the Mediterranean Sea (Pinardi and Masetti 2000)
River discharge into the Mediterranean Sea: Climatology and aspects of the observed variability
(Struglia, et al 2004)
Ocean processes in climate dynamics: global and Mediterranean examples (Malanotte-Rizzoli, 1994)
Influenced by teleconnections with some major climate variability modes:
- - Correlation between ENSO and Western Mediterranean precipitation with opposite signs in autumn
and in spring and varying at the multidecadal time scale (Rodo et al, 1997; Mariotti et al, 2002; Park,
2004; Brönnimann et al, 2007, …).
- - Mechanism involving partly the atmospheric bridge between tropical Pacific and Atlantic, the
perturbation of the Atlantic Walker and Hadley circulation and the propagation of the signal through
stationary Rossby waves and transient eddies (Rodo, 2001; Cassou, 2001; Mariotti et al, 2005, …).
-- Correlation between NAO and Mediterranean precipitation with negative (positive) anomalies for
positive (negative) phase of the oscillation (Hurrell et al, 2003…).
-- Mechanism involving the northward (southward) shift of the storm track during the positive (negative)
phases of the oscillation (Hurrell et al, 2003…).
--Correlation between the semi-permanent subsidence structure over the Eastern Mediterranean and
the onset of the Asian Monsoon. Mechanism involving a Rossby wave propagating northwestward
from the monsoon region (Rodwell and Hoskins, 1996; Ziv et al, 2004; …).
-- Correlation between hot summers in the Mediterranean and the monsoon regime over West Africa.
Mechanism involving moisture transport and meridional thermal contrast (Rowell, 2003;…)
Questions/Objectives:
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Documenting the components of the hydrological cycle over the
Mediterranean (P, E, E-P, SST, S, etc.)
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Estimation and understanding of the interannual variability
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The Variations of the components (time series of anomalies, annual cycles)
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Detection of the trends
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East/West Mediterranean Basin differences
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Evaporation-Salinity connection over the East Mediterranean
Data:
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GPCP: 1979-2004, monthly, (2.5°x2.5°), 1 level
CMAP2:1979-2006, monthly, (2.5°x2.5°), 1 level
CRU: 1979-2001, monthly, (0.5°x0.5°), 1 level
ERA40: 1958-2001, monthly, (2.5°x2.5°), 23 levels
OAFlux (Objectively Analyzed Air-Sea Fluxes for the Global Oceans):
1981-2002, monthly, (1°x1°), 1 level
QuikScat: 1999-2006, monthly, (1°x1°), 1 level
ISCCP radiation: 1984-2004, monthly, (2.5°x2.5°), 1 level
GRDC (Global Runoff Data Center, UNH): Climatology (1807-1991)
HadSST: 1901-2003, monthly, (1°x1°), 1 level
Reynolds SST: 1981-2005, monthly, (1°x1°), 1 level
MedAtlas: Climatology (2002), (0.2°x0.2°), 25 levels
Levitus94: Climatology (1994), (1°x1°), 19 levels
WOA05: Climatology (2005), (1°x1°), 24 levels
SODA1.4.2: 1958-2001, monthly, (0.5°x0.5°), 40 levels
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new GODAS!
New River discharge data – NCAR (Trenberth, Dai), monthly
Climatological mean precipitation and evaporation from ERA40 (1979-1999).
Amplitude and phase (1st harmonic), contours are mean annual cycle in mm/day.
Climatological mean Hadley SST and Medatlas Salinity.
Amplitude and phase (1st harmonic), contours are mean annual cycle in deg C.
Clim: Precipitation (mm/day) ERA40 (58-01)
P over the sea:
- Direct measurements: complex and rare
- Use of reanalysis helps
- No validation and/or low resolution data over sea
- Strong variability
Clim: Evaporation (mm/day) ERA40 (58-01)
E over the sea:
- Leading term of the water budget variability
- Very few measurements
- Low resolution and low quality of the current database
- Problem with physical parametrizations: low confidence in the reanalysis estimations
Clim: E-P (mm/day) ERA40 (58-01)
Motivations for E-P Climate Change:
- Strong impact of the climate change on E-P-R (E increases, P and R decrease)
- large uncertainties (Somot et al, 2006)
- E-P-R is a key term of the Medit. Slow water cycle
- it drives the dense water formation process
Clim: Vertically integrated Moisture Flux (1000-300 hPa) ERA40 (58-01)
Atmospheric humidity convergence:
-Difficult to compute (non-linearity, non conservative in reanalysis,
high temporal and spatial variability, complex Med catchment limit)
-External influences: NAO, African and Indian monsoon
-Impact of the air-sea coupling
Brown=divergence, green=convergence
River runoff fluxes:
-Large uncertainties in the models
-Local and global impact on the Med sea hydrology
Total runoff (mm/mo)
Clim: Runoff GRDC (58-01)
Clim: MSLP (hPa) ERA40 and QuikScat sfc winds (m/s)
- More northward westerlies during summer, descending branch of the Hadley circulation
- the influence of the westerlies over Med during winter
Clim SST and S MedAtlas
sfc level
ISCCP (84-04) Net SW radiation (W/m2)
ISCCP (84-04) Net radiation=SWd-SWu+LWd-LWu (W/m2)
-Positive radiation budget
- low albedo of the sea
Why do we need air-sea heat fluxes?
The atmosphere interacts with the ocean through the exchange of heat, fresh
water, and momentum at the air-sea interface. The air-sea heat exchange
includes a number of processes: solar radiation, longwave radiation, sensible
heat transfer by conduction and convection, and latent heat release by
evaporation of sea surface water. The amount of heat exchange resulting from
these radiative and turbulent heat transfer processes is called air-sea heat
flux.
OAFlux clim (81-02)
ERA40 clim (79-01)
OAFlux clim (81-02)
ERA40 clim (79-01)
The water budget
Terms of the Mediterranean Water Budget:
-Atmosphere-land-hydrology-sea interaction
-Local cycle under global influence (atmosphere, ocean)
-Non regular Mediterranean river catchment
Water budget
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2.
3.
Heat budget
1. Solar and latent heat fluxes are dominant
2. Weak net heat flux
3. Significant seasonal variabilities
Important E values (leading term of the buoyancy), poorly known!
Large seasonal variability of E; long term trend???
Great differences due to the source data, to their resolution, to their variability
Hymex Wokshop, Tolouse, 2007, January, 9-11th, G. Caniaux, L. Prieur, H. Giordani
Med. Atmospheric water budget
P+MFD=E
Era40 79-01 (m2/s2)/100
QuikScat 00-06wind (m/s)
0m
5m
P (1979-2001), 4 seasons of seasonally-averaged time series
r(cmap/era)=0.940
r(gpcp/era)=0.915
r(cmap/gpcp)=0.973
r(cmap/era)=0.961
r(gpcp/era)=0.967
r(cmap/gpcp)=0.996
r(cmap/era)=0.881
r(gpcp/era)=0.864
r(cmap/gpcp)=0.972
r(cmap/era)=0.944
r(gpcp/era)=0.916
r(cmap/gpcp)=0.973
r(95%sl) = 0.43
E (1979-2001), 4 seasons of seasonally-averaged time series
r(oaflux/era)=0.849
r(oaflux/era)=0.918
r(oaflux/era)=0.763
r(oaflux/era)=0.923
r(95%sl) = 0.43
E-P (1981-2001), 4 seasons of seasonally-averaged time series
r(oaf-cmap/era)=0.841
r(oaf-gpcp/era)=0.843
r(oaf-cmap/oaf-gpcp)=0.981
r(oaf-cmap/era)=0.916
r(oaf-gpcp/era)=0.932
r(oaf-cmap/oaf-gpcp)=0.997
r(oaf-cmap/era)=0.785
r(oaf-gpcp/era)=0.798
r(oaf-cmap/oaf-gpcp)=0.989
r(oaf-cmap/era)=0.704
r(oaf-gpcp/era)=0.716
r(oaf-cmap/oaf-gpcp)=0.990
r(95%sl) = 0.43
Hadley SST (1901-2003), seasonally-averaged time series
SODA S (1979-2001), seasonally-averaged time series, 5m
Hadley SST (1901-2003), 4 seasons of seasonally-averaged time series
S (1979-2001), 4 seasons of seasonally-averaged time series
DJF Trends
MAM Trends
JJA Trends
SON Trends
E / W Med!!!!
Atmospheric water balance!
Spatial correlations between GPCP precipitation and local Hadley SST (1979-99)
- based on monthly data (Lag referred to SST)
R(95%sl) = 0.25
Spatial correlations between GPCP precipitation and local SODA Salinity (1979-01)
- based on monthly data (Lag referred to S)
R(95%sl) = 0.24
Spatial correlations between GPCP precipitation and local SODA Salinity (1979-01)
- based on monthly data (Lag=-1 referred to S)
Lag = -1
S FMA with P MAM
S MJJ with P JJA
S ASO with P SON
R(95%sl) = 0.24
Spatial correlations between OAFlux evaporation and local SODA Salinity (1981-01)
- based on monthly data (Lag referred to S)
R(95%sl) = 0.25
Negative corr b/w SST and P => atmosphere is forcing ocean!
Positive corr b/w SST and P => ocean is forcing atmosphere!
W Med
E Med (DJF, MAM)
E, SST
P
S
E Med (JJA, SON)
Contributions/Conclusions:
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Comprehensive view of hydrological components over the Med (new data)
The connection between the anomalies - an evolution of the anomalies in last decades
shows strong signal of recent climate change!
East/West Mediterranean basin differences - understanding the mechanisms of the
hydrological components (ocean-atmosphere interaction) and ocean thermohaline
circulation
The role of salinity has been neglected until recently (the historical lack of
observations and predictive skill enabled by wind forcing and subsurface temperature
observations)
The relative importance of SSS in the context of understanding the mechanisms
The impact of the Mediterranean ocean-atmosphere coupling is dominant at the
regional scale and significant at the global scale.
Mediterranean Sea is an important point of interest (local, regional, global), with a
teleconnection with the general atmospheric circulation
The first preliminary results – a comparison of new available data, a new method of
analyzing anomalies, trends and differences in the east/west Mediterranean with the
mechanism explanations!