Synoptics and dynamics Long Term Mean Climatological overview Possible impacts of the NAO on atmospheric pollution over the WM First evaluation of the climatological conditions during Summer ID: 414754
Download Presentation The PPT/PDF document "Atmospheric conditions featuring the sum..." is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
Atmospheric conditions featuring the summer over the WM
Synoptics and dynamics – Long Term Mean Climatological overview.Possible impacts of the NAO on atmospheric pollution over the WM.First evaluation of the climatological conditions during Summer Charmex campaigns – 2012, 2013, and 2014.
1Slide2
H
L
L
L
H
H
H
Azores High
Thermal low – West African Monsoon
Saharan High – Subtropical High
SLP
GPH – 500
hPa
GPH – 850
hPa
GPH – 700
hPa
Summer synoptic conditions over the WM (LTM 1981-2010) Slide3
Hadley and Walker
circulations affecting the Med. Basin
African Monsoon
Asian Monsoon
3Slide4
Closed cell circulation of the Asian Monsoon
depicted by the vertical zonal cross section averaged over the 20-35°N latitudinal band of wind vectors for July-August (NCEP/NCAR LTM 1957-98) (from: Ziv, et al., 2004).
The WM is further away from the descending branch of the Asian Monsoon cell leading to weaker subsidence
4
Walker Cell - Asian Monsoon
Inversion in the winds (upper level subsidence vs. low-level rising air) is distinctly different for both basins!
Western Mediterranean
Eastern MediterraneanSlide5
Subsiding air masses over the WM is tenfold weaker as compared to the EM!
(0.1 – 1 cm s-1 )
Both combined cell circulations result in a weaker subsiding air masses as compared to the EM possibly acting as lid for dispersion of pollutants over the Med. Basin.
Downdraft
Updraft
Updraft generated by the West African Monsoon
5
1.0
0.1
Jun-Aug. LTM Omega vertical motion (Pa s
-1
) at 850
hPa
(NCEP/NCAR LTM (1981-2010)Slide6
Air mass transport – Climatology JJA 1981-2010
Wind Vector – 1.5 km
Wind Vector – 5.5 km
Wind Vector – 3.0 km
Wind Vector – 9.0 km
1 – 4 m/s
13 – 16 m/s
10 – 13 m/s
6 – 8 m/s
6
Stronger mid-
tropospheric
flow over the WMSlide7
7
Atmospheric dispersion and transport conditions over both Med. Basins during summer (NCEP/NCAR Reanalysis LTM)
Subsiding air mass bases
Western Med.
Eastern
Med.
Asian
Monsoon – Walker Cell
4.5 km
1.0 km
Omega
850hPa Downdraft motion0.1 cm s-1
1.0 cm s-1Wind Vector 3-5.5 km
8 – 11 m s-1 6 – 8 m s-1
The WM is characterized by weaker subsiding conditions and stronger
winds at mid-tropospheric layers.Slide8
NAO +
NAO -
This winter type oscillation controls the strength and direction of westerly winds and storm tracks across the north Atlantic.
Beside climatic conditions NAO affects climatic derived conditions (i.e., air pollution transport)
8
Possible impacts of the NAO on atmospheric pollution over the WM.Slide9
9
Composite means and anomalies of meteorological parameters characterizing extreme NAO+ and NAO- years over the WM over the 65-yr recordSlide10
10
SLP composite means and anomalies for JJA NAOI extreme summers (1950-2014)
NAOI
83
= 1.26
NAOI
94
= 1.07
Mean (1983,1994)
SLP slightly higher over the WM
NAOI
2012
= - 1.61
NAOI
2009
= - 1.18
SLP slightly lower over the WM
NAO
+
NAO
-
Anomaly = Mean
83,94 – LTM1981-2010
Mean (2009, 2012)
Anomaly = Mean
09,12 – LTM1981-2010Slide11
11
(From: Allan, R. J., and T. J. Ansell, 2006: J. Climate, 19, 5816–5842.)
The positions of SLP anomalies for the 2 highest NAO
+
and NAO
-
years derived are consistent with the study of Allan and Ansell based on 122-y (1881-2003)
NAO
+
NAO
+
NAO
-
NAO
-Slide12
12
U
925
composite means and anomalies for JJA NAOI extreme summers (1950-2014)
NAO
+
NAO
-
Slightly weaker zonal wind over the WM
Slightly stronger zonal wind over the WM
Mean (1983,1994)
Mean (2009, 2012)
Anomaly (1983,1994)
Anomaly (2009, 2012)Slide13
13
T
925
composite means and anomalies for JJA NAOI extreme summers (1950-2014)
NAO
+
NAO
-
Slightly warmer air over the WM
Much warmer air over the WM
Mean (1983,1994)
Mean (2009, 2012)
Anomaly (1983,1994)
Anomaly (2009, 2012)Slide14
New
results
from
Pierre
Nabat
Dust
outbreaks
and
weather regimes
NAO-
Atlantic
Low
/ NAO +
Blocking
Atlantic
Ridge
Dust
AOD
Sea
level
pressure
Summer
(JJA)
weather
regimes
(anomalies
) / Climatologies 1980/2012Slide15
Conditions during Summer ChArMEx
campaigns – JJA Composite Means and Anomalies for 2012, 2013, and 2014.15
Sea-level pressure
700
hPa
Zonal Wind
925 hPa
Air Temperature Slide16
SLP Mean: Jun-Aug 2012
SLP
Anom
: Jun-Aug 2012
Anomaly = Mean
2012
– LTM
1981-2010
NAO = - 1.61
Deepening of the Icelandic low and withdrawal west and weakening of the Azores High, whole Med. Basin more cyclogenetic.
Negative SLP anomalies over the Med. Basin.
Summer 2012
16
Sea-Level PressureSlide17
SLP Mean: Jun-Aug 2013
SLP
Anom
: Jun-Aug 2013
Anomaly = Mean
2013
– LTM
1981-2010
NAO = 0.72
Intensification and progression eastward of the Azores High and less cyclogenetic conditions over WM.
Positive SLP anomalies over the Western Med. Basin.
Summer 2013
17
Sea-Level PressureSlide18
SLP Mean: Jun-Aug 2014
SLP
Anom
: Jun-Aug 2014
Anomaly = Mean
2014
– LTM
1981-2010
NAO = - 0.81
Near normal strength and position of the Azores High.
Slight negative SLP anomalies over the Western Med. Basin.
Summer 2014
18
Sea-Level PressureSlide19
Stronger zonal wind comp. (3 km) during NAO
- summers (2012, 2014)Weaker zonal wind comp. (3 km) over the basin during NAO+
summer (2013)
19
700
hPa
Mean - 2012
700
hPa
Mean - 2014
700
hPa
Mean - 2013
U
700
composite means for JJA
NAOI for summer 2012/13/14 Slide20
20
925
hPa
Temp
Anom
. 2012
925
hPa
Temp
Anom. 2014925
hPa Temp Anom. 2013Colder air temperature over the WM during NAO
+ summer (2013)
Warmer air temperature over the WM during NAO- summer (2012)
Air TemperatureSlide21
Daily
weather
regimes
in
2012
Summer
2012
NAO –
Blocking
Atlantic Ridge
Atlantic Low / NAO +Slide22
22
Large-scale atmospheric dispersion and transport conditions
are favored
over
the WM
contrary to
the EM.
In spite of the summer NAO (SNAO) smaller variability and spatial extent, extreme SNAO suggest that:
SNAO- : WM more
cyclogenetic, stronger winds, warmer as compared to SNAO+
Summer 2012 (NAOI = -1.6) Weak Azores High, Med. Basin more cyclogenetic than its summer LTM as indicated by stronger zonal winds at mid-
tropos. and warmer air temp.
Summer 2013 (NAOI = 0.72) Eastward penetration of Azores High, less cyclogenetic conditions over W. Med., weaker winds at mid-
tropos. and colder air temp.
Summer 2014 (NAOI = -0.81). Slightly lower SLP, slightly stronger zonal winds over the W. Med.
Very preliminary conclusions….Slide23
The following slide exposes the possible issues for the discussion
23Slide24
24
Is the first statement true and does it hold for all summers? Is the second statement true ?
If indeed true, can this rule of thumb be turned upside down by internal climate variability (e.g. NAO)?
Can we point on the responsible for the unexpected low pollution concentration (emitting sources/ diluting conditions) in 2012,13 and 14?
Do we have enough pollutants data to
assess
if these conditions differ much for 2012, 2013 and 2014?
1. Large-scale atmospheric dispersion and transport conditions
are favored over
the WM contrary to
the EM: The WM is characterized by weaker subsiding conditions and stronger winds. 2. Summer NAO
- years favor dispersion and transport over the WM: More cyclogenetic and stronger winds.