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full low cloud covariance per standard deviation of omega
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
synoptic only covariance
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
diurnal covariance
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.06
−0.04
−0.02
0
0.02
0.04
0.06
Covariance of ISCCP adjusted low cloud with EIS. Posi9ve values (red) in the subtropics and eastern tropical Atlan9c and Pacific Oceans indicate cloud amounts are greater for more stable condi9ons. Nega9ve values (blue) poleward of 45° la9tude show cloud amount increases for unstable condi9ons.
• Synop9c (1-‐30 day) covariance is responsible for most of the total covariance (posi9ve and nega9ve) poleward of ±15° la9tude, including in the stratus regions.
• In the deep tropics, seasonal covariance of cloud and EIS is responsible for much of the total covariance, especially over the eastern tropical Pacific and Atlan9c Oceans.
Amplitudes are normalized to represent cloud frac9on anomalies associated with a standard devia9on of EIS.
References Clement, A. C., R. Burgman, and J. R. Norris, 2009: Observa9onal and Model Evidence for
Posi9ve Low-‐Level Cloud Feedback. Science, 325, 460-‐464. Klein, S. A., and D. L. Hartmann, 1993: The seasonal cycle of low stra9form clouds. J.
Climate, 6, 1588-‐1606. Rossow, W. B., and R. A. Schiffer, 1999: Advances in understanding clouds from ISCCP. Bull.
Amer. Meteorol. Soc., 80, 2261-‐2287. Wood, R., and C. S. Bretherton, 2006: On the Rela9onship between Stra9form Low Cloud
Cover and Lower-‐Tropospheric Stability. J. Climate, 19, 6425-‐6432, 10.1175/JCLI3988.1.
The authors acknowledge Joel Norris for his guidance in adjus@ng for satellite ar@facts in ISCCP cloud. This work was supported by the Office of Science (BER) U.S. Department of Energy grant DOE ASR DE-‐SC0006994.
Marine low clouds and inversion strength Simon P. de Szoeke1*, Sandra E. Yuter2, David B. Mechem3
1Oregon State University, Corvallis. 2North Carolina State University, Raleigh. 3University of Kansas, Lawrence. *corresponding author email address: [email protected]
low cloud standard deviation
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
0
0.1
0.2
0.3
low cloud synoptic standard deviation
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
0
0.1
0.2
0.3
low cloud seasonal standard deviation
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
0
0.1
0.2
0.3
CERES "D1" 2000−2011 daylight low cloud amount
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
0
0.2
0.4
0.6
0.8
Top: Mean low cloud amount (CERES daylight-‐only) shows subtropical marine stra9form cloud decks near the Klein and Hartmann (1993) stratus regions (squares). Low cloud is defined to have cloud top below 560 hPa to include clouds in deep boundary layers. Right: ISCCP standard devia9on of low cloud amount (~0.3) is dominated by synop9c varia9ons, with a 0.1 contribu9on from the seasonal cycle in the southern stratus decks.
diurnal
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.02
−0.01
0
0.01
0.02
interannual
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.015
−0.01
−0.005
0
0.005
0.01
0.015
full−(interannual+seasonal+synoptic+diurnal)
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.015
−0.01
−0.005
0
0.005
0.01
0.015
Low clouds cool the climate by reflec9ng sunlight, shading the ocean surface, and emijng thermal radia9on at a warm temperature. Marine low cloud amount is correlated to lower tropospheric stability (θ700hPa-‐θsfc) on seasonal and interannual 9me scales (Klein and Hartmann 1993). Low cloud parameteriza9ons in many models are ac9vated by lower tropospheric stability criteria. Es9mated inversion strength (EIS, Wood and Bretherton 2006) measures inversion strength using standard analysis levels. A stronger inversion is presumed to limit entrainment of dry air into the boundary layer, aiding cloud forma9on and limi9ng cloud evapora9on. As surface climate warming would reduce inversion strength and thus cloud amount, the control of the inversion strength on marine low cloud represents a posi9ve climate feedback. We inves@gate the low cloud-‐EIS rela@on on sub-‐daily to interannual 9me scales with 26-‐years of ISCCP D1 adjusted low cloud frac9on (Rossow and Schiffer 1999, Clement et al. 2009) and EIS from NCEP reanalysis. We find: 1. Synop@c variability is responsible for most EIS-‐low cloud covariance throughout the subtropics and midla9tudes. Nega9ve synop9c covariance (unstable-‐cloudy) is found at 45-‐60° la9tude. Synop9c storm structure explains the midla9tude covariance.
2. The seasonal EIS-‐low cloud (stable-‐cloudy) correla9on (Klein and Hartmann 1993) dominates only in the southeastern tropical Atlan9c and Pacific Oceans. Beware of using Klein-‐line low cloud parameteriza@ons on @mescales other than seasonal.
3. Diurnal and interannual low cloud-‐EIS covariance are 10x smaller than seasonal or synop9c variability.
4. Synop9c covariance of low cloud with downward ver@cal velocity is found in midla9tude storm tracks, especially over the western north Pacific and Atlan9c Oceans.
The seasonal inversion strength varia@ons explain a small frac@on of low cloud variance around the globe. The processes responsible for marine low cloud correla@ons should be considered carefully when extrapola@ng these correla@ons to climate feedbacks.
Interannual to diurnal power spectra of ISCCP adjusted cloud, EIS, and 700 hPa pressure velocity in the tropical stratus regions. Considerable energy lies in the broad synop9c band around 10-‐day period. We separate EIS and low cloud amount covariance into orthogonal interannual, seasonal, synop9c, and diurnal bands.
longitude
la9tud
e
Low cloud varia9ons associated with diurnal and interannual varia9ons of EIS are small.
longitude
la9tud
e
full low cloud covariance per standard deviation of omega
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
synoptic only covariance
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
diurnal covariance
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.06
−0.04
−0.02
0
0.02
0.04
0.06
la9tud
e
4. longitude
upward-‐cloudy
downward-‐cloudy
3.
What is responsible for the synop@c midla@tude low-‐cloud EIS covariance?
Synop9c pamerns of EIS and low cloud regressed on downward 700-‐hPa pressure velocity at 44°S, 61°E (cross).
The EIS regression on pressure velocity 9lts northeast-‐southwest in the southern hemisphere, while low cloud amount 9lts northwest-‐southeast. Thus more low clouds are found in stable condi9ons equatorward of 45° and more low clouds are found in unstable condi9ons poleward of 45°, explaining the synop9c low cloud-‐EIS correla9on (1) at len.
Low clouds increase ~0.15 for a standard downward anomaly of 700 hPa pressure velocity (ω700) in midla9tudes, especially the western Pacific and Atlan9c storm tracks, and the Atlan9c and Indian Southern Ocean.
Low cloud response to ver9cal velocity is weak outside the midla9tudes, with clouds increasing slightly for upward mo9on outside of tropical convergence zones.
low cloud−EIS covariance per standard EIS anomaly
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.1
−0.05
0
0.05
0.1
synoptic
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.1
−0.05
0
0.05
0.1
seasonal
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.1
−0.05
0
0.05
0.1
low cloud−EIS covariance per standard EIS anomaly
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.1
−0.05
0
0.05
0.1
synoptic
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.1
−0.05
0
0.05
0.1
seasonal
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.1
−0.05
0
0.05
0.1
low cloud−EIS covariance per standard EIS anomaly
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.1
−0.05
0
0.05
0.1
synoptic
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.1
−0.05
0
0.05
0.1
seasonal
60 90 120 150 180 −150 −120 −90 −60 −30 0 30 60−60−45−30−15
0
15304560
−0.1
−0.05
0
0.05
0.1
less stable cloudy
more stable cloudy
longitude
la9tud
e
1.
2. la9tud
e la9tud
e
10!3 10!2 10!1 100
NEP20-30°N120-130°W
10!3 10!2 10!1 100
NEA15-25°N25-35°W
10!3 10!2 10!1 100
SEP10-20°S80-90°W
10!3 10!2 10!1 100
SEA10-20°S0-10°E
10!4
10!3
10!2
10!1
100
101
102
103
10!4
10!3
10!2
10!1
100
101
102
103
10!4
10!3
10!2
10!1!1
100
101
102
103
10!4
10!3
10!2
10!1
100
101
102
103
powe
r spe
ctral
dens
ity [p
ower
/ day
]
!1frequency [day ]
inversion strength [K]
cloud amount
" [Pa s ]700 hPa!1
seasonal diel
inversion strength
20 40 60 80 100 120−70−65−60−55−50−45−40
−35
−30
−25
−1
−0.5
0
0.5
1
longit
ude
low cloud
20 40 60 80 100 120−70−65−60−55−50−45−40
−35
−30
−25
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
omega (+downward)
longitude
20 40 60 80 100 120−70−65−60−55−50−45−40
−35
−30
−25
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
K
EIS anomaly correlated to downward velocity at
H L
inversion strength
20 40 60 80 100 120−70−65−60−55−50−45−40
−35
−30
−25
−1
−0.5
0
0.5
1
longit
ude
low cloud
20 40 60 80 100 120−70−65−60−55−50−45−40
−35
−30
−25
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
omega (+downward)
longitude
20 40 60 80 100 120−70−65−60−55−50−45−40
−35
−30
−25
−0.15
−0.1
−0.05
0
0.05
0.1
0.15
H L la9tud
e stable-‐cloudy
unstable-‐cloudy
low cloud anomaly correlated to downward velocity
longitude
geopoten9al height contours every 10 m
rms:0.12
rms: 0.09
rms:0.04
rms:0.05
rms:0.005
diurnal
interannual
In lower panel, outline-‐contour EIS anomaly over shaded cloud anomaly, to see posi9ve and nega9ve covariance bands bemer.
This is due to compe99on between low clouds and high clouds. High clouds obscure low clouds to the satellite.
!
!
room 1 poster 57
45°S
clow’s’ < 0
clow’s’ > 0 ____
____ – – –
– – –
–
+ + + +
+
+
+
–
+ +
+ +
+ +
+ +
+
– – –
– –
–
– – –
– –
– –
+ + + + +
+
southern hemisphere