Cloud observations: the state of the art Alexander Chernokulsky A.M. Obukhov Institute of...

Cloud observations:the state of the art

Alexander Chernokulsky

A.M. Obukhov Institute of Atmospheric Physics Russian Academy of [email protected]

NABOS 2013Ak. Fedorov, August 21 – September 22, 2013

Outline

I. Cloudiness in the Earth climate system.

II. A brief history of cloud observations and up-to-date cloudiness data.

III. Cloud observations training on NABOS-2013.

Alexander Chernokulsky Cloud observations: the state of the art

I. Cloudiness in the Earth climate system


Two roles of cloudiness

Cloudiness play two important roles in the Earth climate system:

1.Clouds are essential stages in the cycling of water between the earth and atmosphere. Clouds act both as sources and sinks of water vapor and in its turn water vapor is fundamental to the formation of clouds.

2.Clouds are a key component of the Earth radiation balance. The �thermal absorbent character of water is greatly enhanced when in a �condensed phase. On a molecule-by-molecule basis, water in either solid or liquid form in the atmosphere absorbs more than 1000 times more strongly than in gaseous form. So clouds contribute to the greenhouse effect. On the other hand, clouds reflect a fraction of the solar radiation that would otherwise be absorbed at the Earth’s surface.


The global annual mean energy balance


Numbers indicate best estimates for the magnitudes of the globally averaged energy balance components together with their uncertainty ranges, representing present day

climate conditions at the beginning of the twenty first century. Units W m-2 . Wild et al., 2012

Cloud radiative forcing (effect)


Harrison et al., 1990; Stephens et al., 2012

Annual mean net (SW+LW) cloud radiative forcing

Cloud radiative forcing (effect) can be estimated as the difference between clear-sky and total-sky fluxes (for LW and SW).



Global annual mean shortwave cloud radiative forcing (so-called albedo effect of clouds):

-47.5 ± 0.3 W m-2

The main contributor to the SW CRF: stratus and strato-cumulus decks over eastern part of the oceans with high albedo (up to 70%) and small temperature contrast with the underlying surface (just 10ºC colder => small greenhouse effect) – potential for geoengineering+ clouds in midlatitude stormtracks in summer hemisphere.

Global annual mean longwave cloud radiative forcing (so-called greenhouse effect of clouds):

26.4 ± 0.4 W m-2

The main contributor to the LW CRF: high thin (subvisible) cirrus cloud decks in tropics with very cold tops. They transmit downward solar radiation without significant scattering or absorption, while blocking a larger fraction of the outgoing longwave radiation and reradiating it to space at very low temperatures.



Global annual mean net cloud radiative forcing:

-21.1 ± 0.5 W m-2

So, globally, clouds cool the Earth (mostly by reflection of sunlight from clouds in the mid-latitude summer hemisphere).

Regional values of cloud radiative forcing can reach 100-150 W m-2 of both signs.

Thus, clouds play an important role in the Earth climate system, they act in both global and regional scales.We should observe cloudiness with the accuracy.

II. A brief history of cloud observations and up-to-date cloudiness data.


A history of cloud classifications


• 1776. The first classification of clouds by naturalist J.-B. Lamark from France (he suggests 5 and after that 7 cloud types, but his classification had no spreading).

• 1802. Pharmaceutist Luke Howard from England invent Latin-based names for three main morphological type of clouds: Cirrus (means “feather”), cumulus (means “heap”) and stratus (means “layer”). His classification with some amendments (the major ones were proposed in 1887 by Hilderbrandson and Aber-Cromby) is used for now.

• 1896. The first international cloud atlas with 30 color lithographs. 1930: the second edition of the international cloud atlas (75 photo pictures: from land and from planes); 1956: the third edition (101 photos) and so on...

• 1980-90s. Satellite cloud classification (not morphological, clouds divided by cloud optical thickness and cloud top pressure).

Morphological cloud classification


NimbostratusNs

StratusSt

CumulusCu

StratocumulusCu

AltocumulusAc

CirrocumulusCc

AltostratusAs

CirrostratusCs

CirrusCi

CumulonimbusCb

High-levelclouds(Hbase>7-10 km,In the Arctic: Hbase>5 km)

Middle-levelclouds(Hbase>2 km,In the Arctic: Hbase>1.5 km)

Low-levelClouds

Satellite cloud classification


Rossow and Schiffer, 1999

Cloud datasets


Cloud datasets

Observations

Surface-based

Aerological

Satellite

Results of numerical simulations

ReanalysesGeneral circulation

models

From airplanes

Meteorologicalradars

Visualobservationsby observers

Automated(sky-cameras etc.) Passive Active

Combined

Annual zonal mean of total cloud fraction (TCF)SH NH


Seasonal difference of zonal mean of TCF

Zonal-mean difference of total cloud fraction between June-July-August and December-January-February


SH NH

Satellite observationsGround-based observationsReanalyses data

GCM simulations

Global annual mean of total cloud fraction

Cloud fraction over the ocean

Clou

d fr

actio

n ov

er la

nd

0.3 0.4 0.5 0.6 0.7 0.80.3

0.4

0.5

0.6

0.7

0.8

Cloud fraction over

land and ocean

over the ocean:~0.7 (от 0.6 до 0.77)

over land:~0.55 (от 0.41 до 0.69)

TCF according to observations:

Over ocean and land:~0.66 (от 0.56 до 0.75)


Chernokulsky, 2010

III. Cloud observations training on NABOS-2013


Why it is so important?


All meteorological observations from ships go to International archive and provide unique information

about oceans’ weather (including clouds of course)

Monthly means number of cloud observations

(average for 1956-2007).

Cloud observations: the state of the art Alexander Chernokulsky A.M. Obukhov Institute of...

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