Observation of upper atmospheric clouds

(Section 2.7.8)

The nacreous clouds and noctilucent clouds should be identified primarily based on the definitions and descriptions of upper atmospheric clouds.

When these upper atmospheric clouds are observed, an exact record must be kept of the date, time and location of the observation. The position of the clouds in the sky should be recorded, and photographs should be taken, whenever possible.

In the case of noctilucent cloud, the azimuth (left and right extent) of the display, and the elevation above the horizon of the upper edge of the cloud (and lower edge if there is one) should be recorded. The brightness of the cloud, on a five-point scale, and, if possible, its structure and classification should also be determined — (see Table 11 for specific details of the brightness scale and noctilucent cloud classifications). Variations in brightness and classification through the period of observation should also be recorded.

The general observing conditions should also be noted; for example, the presence of haze, mist and any tropospheric clouds. The presence of aurora occurring simultaneously with noctilucent clouds should also be noted.

If the observer is unable to determine the azimuth or elevation of noctilucent clouds at the time of the observation, a careful note should be made of the extent of the cloud relative to topographic features, and the elevation relative to any bright stars that are visible in the vicinity of the clouds. By providing such reference marks, the extent and elevation of the clouds may be determined later.