ERA40 surface fluxes (DJF) trade wind belts warm advection cold - - PowerPoint PPT Presentation

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ERA40 surface fluxes (DJF) trade wind belts warm advection cold air outbreaks Lecture 14, Slide 1 Cloud-topped BL processes Siems et al. 1993 Lecture 14, Slide 2 Some marine boundary-layer cloud types WMO cloud classification:

SLIDE 1

Lecture 14, Slide 1

ERA40 surface fluxes (DJF)

cold air outbreaks

warm advection trade wind belts

SLIDE 2

Lecture 14, Slide 2

Cloud-topped BL processes

Siems et al. 1993

SLIDE 3

Lecture 14, Slide 3

WMO cloud classification:

http://www.srh.noaa.gov/jetstream/synoptic/clouds_max.htm#max

Some marine boundary-layer cloud types

Cumulus (Cu) Cu under Sc Cumulonimbus

ARM Image Library

Stratocumulus (Sc) Stratus (St) Fractostratus

SLIDE 4

Lecture 14, Slide 4

June 9, 1994 GOES-West

Deep convection Shallow cumulus

Marine boundary layer clouds from space

Stratocumulus Stratus

SLIDE 5

MBL Lecture 1, Slide 5

Observations over the oceans

Transition from Sc - shallow Cu - deep Cu as temperature of sea-surface

rises compared to that of mid-troposphere. JJA Cb Cu Sc St

SLIDE 6

Lecture 14, Slide 6

‘stratus’ = stratus + stratocumulus + fog

SLIDE 7

MBL Lecture 1, Slide 7

Boundary-layer cloud amount and cloud radiative effect

Marine boundary-layer cloud is the most radiatively

important cloud type for the current climate.

Low cloud amount (%) Net CRE [W m-2] correlated with… CRE = change in net (shortwave+longwave) radiation into TOA due to clouds. BL clouds reflect sunlight but are too warm to much affect

utgoing longwave radiation,

producing a negative SWCRE and little LWCRE, for negative net CRE.

SLIDE 8

MBL Lecture 1, Slide 8

Warren surface cloud climatology

http://www.atmos.washington.edu/CloudMap
45 years of routine ship observations

advection from warm to much colder SST advection from warm land to cold SST

Coasts Cold tongue

N of Gulf Stream, Kuroshio

Norris et al. (1998, J Climate)

SLIDE 9

MBL Lecture 1, Slide 9

Cold-ocean MBL cloud types

Weak air-sea temperature differences Deep storm systems

Norris et al. (1998, J Climate)

SLIDE 10

MBL Lecture 1, Slide 10

Cool-ocean MBL cloud types

Cold advection, cool SST

Cold air outbreaks

Cold advection, medium SST

SLIDE 11

Lecture 14, Slide 11

SLIDE 12

MBL Lecture 1, Slide 12

Cumulus-topped MBLs

Over warm oceans, Cu-topped MBLs > 70% of time.

Norris et al. (1998, J Climate)

SLIDE 13

Lecture 14, Slide 13

Subtropical PBL soundings

Sc and St clouds favored by strong, low inversions, which go with

large lower tropospheric stability.

LTS

Bretherton 1997, after Albrecht et al. 1995

SLIDE 14

Measures of lower-tropospheric stratification

Lecture 14, Slide 14

Lower tropospheric stability (Klein&Hartmann 1993) LTS = θ700 - θ1000 Estimated Inversion Strength (Wood&Breth 2006) EIS = LTS – Γma,850(z700 – zLCL) WB06 WB06

SLIDE 15

EIS correlated to low cloud everywhere, LTS correlated to low cloud in low latitudes

Lower tropospheric stability correlated with low-latitude marine low cloud (Klein and Hartmann 1993) EIS also captures midlat BL cloud underlying a cooler free troposphere: EIS is a more ‘temperature- invariant’ predictor of low cloud response to stratification change.