Introduction to Cloud Structures

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Do you see yonder cloud that's almost in shape of a camel?

By the mass, and 'tis like a camel indeed.

Methinks it is like a weasel.

It is backed like a weasel.

Or like a whale.

Very like a whale.

William Shakespeare: Hamlet, Prince of Denmark: ACT III. Scene II

- The Cloud Structures

- Methods
- Data Presentation


Clouds are the most mobile and changeable structure in the aspect of our live planet. Approaching the Earth it is impossible to look over their deversity, complexity and striking beauty.

The following work is to describe some cloud formations over the ocean as well as present examples of some of the most frequently found cloud structures.
The work includes the analysis of the notion "a cloud structure" (also known as "a cloud pattern"), the description of these structures, some of inherent physical parameters thereof, the statistics on allocation and a wide range of images.
The data that was received during many years from the MERIS - a programmable, medium-spectral resolution, imaging spectrometer installed on the ESA's satellite ENVISAT served as the source material; the Software BEAM VISAT developed by the Brockmann Consult, Germany, was used as the basic tool.
The work was conducted at the Brockmann Consult, Germany, within the framework of the "Image of the Day" project.

The Cloud Structures (CS)

While observing the Earth from the height of 500-5000 km it is possible to notice that the cloudy envelope of the planet is a ranked rather than a chaotic accumulation of clouds as far as it concerns their forms. These forms either repeat themselves or differ but in any event they reflect definite process taking place in the atmosphere. The outward appearance of CS remains invariable within a year and on the whole does not depend on their geographical location.
All this allows to try to unify them on the base of appropriate criteria and thus to speak about the cloud structures and systemize them.
In this work a "cloud structure" means a compact cloud formation

  • of a distinct spatial form
  • with the dimensions of more than 10-20 km
  • and reflecting a definite state of the atmosphere and the underlying surface.

Very often some CSs may be associated to these or that geographic realities. Formation and expansion of CSs also depend on the season. Some CSs consolidate in large mega structures (MCS). Most of CSs are so large, that to observe them from the surface of the Earth or from one side, for example from the board of an airplane, means to obtain an incomplete picture.
Observation from above, namely from a satellite, may give the information only about the top layer of the structure, but at the same time to cover the whole object.
To see CSs from all sides would be, of course, the perfect choice.

The Distinction between Cloud Structures and Clouds

A Cloud Structure usually differs from the clouds that constitute it. This difference concerns:

  • the dimensions (a CS is much larger)
  • the way of interacting with the environment (the Cloud structures effect on the processes in the atmosphere and the ocean is much more profound than the one of the clouds)


  • CSs may transform in other CSs
  • the processes taking place within a SC may change its looks in different spots whereas it still keeps its integrity and houses various kinds of clouds
  • different CSs may include identical types of clouds.

The clouds constituting CS may serve as markers (an indicator) of the air mass movement. Being structurally unified they themselves influence the atmospheric phenomena.


The firm Brockmann Consult is one of the receivers of the ESA satellite ENVISAT information.
Since 2002 the MERIS data has been transmitted to the firm and then distributed to the ESA consumers world-wide. The software developed by Brockmann Consult processes and collects all arriving fresh data and visualizes it in real resolution (1120 pixels width, pixel Size 1040m x 1200m), so that the data could be studied just after it had arrived.

In 2003 an Internet project "Image of the Day" was launched.
According to the said project the whole body of MERIS level 1 data (covering already more than 27000 orbits) is examined in order to discover interesting nature phenomena, and is then represented as RGB colour pictures. These colours have near resemblance to natural ones.
Thus certain weather events and cloud structures arrested special attention and were stored as RGB pictures.

In 2006 the systematization of the new as well as of the already existing cloud data started.
As the result the data was stored as JPG pictures and grouped pursuant to its types.
The BEAM VISAT software developed on the Brockmann Consult allows visualizing and processing both the MERIS level 1 satellite data and supplementary information.
Fragments of interest will be cut out from whole orbit and visualized e.g. from the TOA radiance band 1 MERIS channel (wavelength: 412.691nm, range 9.937nm) (where the clouds are easily recognized).
They are first possibly contrasted and geographically referenced and then stored, possibly along with the additional information. The name of the stored file contains the date and the orbit number of the fragment.

The BEAM VISAT software allows to observe the MERIS level 2 data as well.
The values of Cloud top pressure, Cloud albedo and Cloud type index, contained in the MERIS level 2 data, are important as cloud characteristics.
The Cloud top height can be calculated by the formula
         h [km] = -8 * LOGS (cloud_top_press [hPa]/1013).

The type of the clouds contained in a cloud structure is indicated in the ESA Cloud type index table.

Optical thickness
Pressure (hPa)

0 - 3.6
3.6 - 23
23 - 379
50 - 440 135 (Cirrus) Ci 136 (Cirrostratus) Cs 137 (Deep convection) Cb
440 - 680 132 (Altocumulus) Ac 133 (Altostratus) As 134 (Nimbostratus) Ns
680 - 1000 129 (Cumulus) Cu 130 (Stratocumulus) Cs 131 (Stratus) St

An example of the "of the Morning Glory" Cloud Structure of 2007.02.08, orbit 25836: (from right to left) RGB image in the visual 412,691 Nm channel, Cloud top height with the Scale in [km], Cloud type index with the Scale.

The BEAM VISAT software allows the whole orbit to be projected on the world map (in the case in question the geographical projection is used). Therefore each cloud structure revealed can be interactively superposed on the map of the world and geographically referenced. Using the daily MERIS data (14 orbits per day) it is possible to make up the picture of the global occurrence, season changes and theobservation frequencies of different cloud structures.
This does not only help to describe the cloud structure, but also enables to better understand the Earth's climate processes.

Examples of observation frequency diagrams (the statistic work is carried on the period of 04.2006-10.06 and 02.07). The darker the point is, the more often observations were made. 
"Close Cells" observation diagram for 06.06"Enhanced Cumulus" observation diagram for 10.06


Data Presentation

To present the most of structures the following data will be offered:

  • The MERIS level 2 data
    • Cloud top height [km]
    • Cloud albedo
    • Cloud type (the clouds, which are contained in structure)
  • Statistic data
    • Global Occurrence
    • Diagram Observation Diagrams (for some structures)
  • The physical explanation for a structure emergent
    • Because the origin and developing of structures is sometimes unclear, the explanation of the physical nature of a structure emergent is offered only as basis for a discussion
  • Pictures of corresponding structure for the time period (mostly) 2006-2012
    • MERIS level 1 RGB or black-and-white with or without geographical references
    • The MERIS level 2 can be attached:
      • cloud top height false colour images
      • albedo false colour images
      • cloud type index false colour images
      • cloud optical thickness false colour images
    • Cloud anaglyph image (in some cases)

Michael Paperin, May 2007 - June 2012, Hamburg, Germany