Cloud the bottom of the hierarchy. Clouds in the troposphere assume five physical forms based on structure and process of formation. These forms are commonly used for the purpose of satellite analysis. They are given below in approximate ascending order of instability or convective activity. "Non-convective" stratiform clouds appear in "stable" airmass conditions and, in general, have flat sheet-like structures that can form at any altitude in the troposphere. The stratiform group is divided by altitude range into the genera cirrostratus (high-level), altostratus (mid-level), stratus (low-level), and nimbostratus (multi-level). Fog is commonly considered a surface-based cloud layer. The fog may form
Sheet music the band to play together. Many guitar players and electric bass players learn songs and note tunes using tablature, which is a graphic representation of which frets and strings the performer should play. "Tab" is widely used by rock music and heavy metal guitarists. Singers in many popular music styles learn a song using only a lyrics sheet, learning the melody "by ear" from the recording. Sheet music can be used as a record of, a guide to, or a means to perform, a song or piece of music. Sheet music enables instrumental performers who are able to read music