Global Cloud Phase Distribution Derived from CloudSat and CALIPSO Measurements

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3 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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Global Cloud Phase Distribution Derived from CloudSat and CALIPSO Measurements

Combined Lidar
-
radar Cloud

Phase Identification


An Example of Cloud Phase Identification



Supercooled water or mixed
phase or ice clouds may exist in the
temperature range 0
-

-
40
O
C.



Combing lidar
-
radar
measurements from space can
provide better cloud phase
identification than lidar or radar
measurements separately:



Radar is more sensitive to ice
particles (lower concentration and
larger size) while lidar is more
sensitive to water droplets (higher
concentration and smaller size)



May avoid the challenge of
multiple scatter effect on lidar
depolarization measurements.



More completed measurements to
cover optically thin and thick clouds.

Cloud Phase Distribution Statistics

water

Ice

-

40
°
C

0
°
C

Supercooled water

or mixed phase

or ice

Cloud Temperature

Ice



Weak

Very

strong

Strong

Mixed


phase

Strong

-

moderate

Ice

Weak

Strong

Water

Radar signal

Lidar signal

Phase

Zhien Wang

University of Wyoming, zwang@uwyo.edu

Kenneth Sassen

University of Alaska

The Flowchart of Combined Lidar
-
Radar Cloud

Phase Identification


a) The fraction of total cloud layer with
cloud base temperature >
-
38.5

C
and top temperature < 0

C.

b) The cloud top temperature
distribution of the above clouds at
a given latitude band.


c) The water cloud occurrence
within a given latitude and
temperature bin.


Ice

Water

Mixed
-
Phase

Cloud Top Temperature


Occurrence (%)


Day and night differences
in occurrence of different
clouds at different latitude :

Day


solid lines

Night


dashed line

The general features of lidar and radar signal
from water, ice, and mixed
-
phase clouds.

Cloud phase identification main inputs:


CloudSat Ze profile


CALIPSO cloud layer products


ECMWF temperature


Z
: Layer thickness


Z_lidar
: Layer thickness from lidar only

B
max
: Layer maximum attenuated backscattering coefficient

Ze
max
: Layer maximum radar reflectivity

T
: Temperature estimated from ECMWF

T
base

<
-
35

C ?

Start
: for a given

cloud layer

Ice

Yes

No

T
top

>
-

5

C ?

Water

Yes

Do both lidar and radar

detect the cloud layer?

Does only lidar detect

the cloud layer?

(T
base

<
-
15) or

[(T
base

<
-
5) and

(T
top

<
-
38.) and

(Ze
max

< 10)]

No,

Only radar
detect the

cloud layer

{(T
base

<
-
5

C) and

[(B
max

< B0) or [(

Z >1.2)


and (B
max

< 1.5 B0)]] and


[(

Z >0.5 or (
T
base

<
-
25

C)]}


or {(
T
base

<
-
25

C) and

(B
max

< 2 B0) and

(T
top

<
-
37

C)}



(

Z <1.2) and

{[(B
max

> B0) and (T
top

>
-
38

C)]


or [(T
base

> 0) and


(T
top

>
-
10)]}

No

No

Water

Yes

Yes

(B
max

> B0) and


(T
top

>
-
35

C) and

(Ze
max
<
-
20 dB)

and (

Z <1.2)

{(T
base

< 0

C) and

[ [(B
max
< B0) or ( T
base_lidar

<
-
30) ]


or [(

Z_lidar >0.85

Z ) and (B
max

< 1.8 B0)

and [ (

Z_lidar >1.7 or (
T
base

<
-
25

C)] ]]}


or {(
T
base

<
-
25

C) and

(B
max

< 2.5 B0) and

(T
top

<
-
37

C)}


Ice

Yes

Water

Yes

Mixed

No

Mixed

No

(

Z <= 0.24) and

(Ze
max

<
-
25 dB)

Ice

Yes

Yes

Ice

No

Water

Yes

Mixed

No

No

Yes

No

19:42 19:44 19:46


19:48 19:50

Time UTC

Height MSL (km)

Radar mask

Lidar mask

Cloud Phase:

Ice

Water

Mixed

Satellite track

Lidar depolarization

532 nm

Ze

T

Jan + Feb

Mar + Apr

May + Jun

Jul + Aug

Sep + Oct

Nov + Dec

Temperature

Temperature

Temperature

Temperature

Latitude Latitude Latitude Latitude Latitude


Latitude

%

Occurrence (all)

Water cloud

Mixed
-

Phase

Ice cloud

a

b

c

d

e

d) The ice cloud occurrence
within a given latitude and
temperature bin.


e) The mixed
-
phase cloud
occurrence within a given
latitude and temperature bin.