Synoptic conditions producing cirrus during the FIRE cirrus IFO

Although direct observations of cirrus clouds by the FIRE research aircraft were usually confined to the area of Intensive Field Observation (IFO) surface network, these cirrus were generally part of a more extensive zone of upper level cloudiness. It is these large scale patterns of cirriform cloud and their relationship to the corresponding synoptic environment which are the prime focus. Three conceptual models are presented and each of the individual cases are classified into one of these categories. Although the cases manifest significant differences in intensity and small scale structure, it is believed that they are best viewed in this unified context. The descriptions given are mostly qualitative, however, quantitative descriptions of the synoptic control and its relationship to cloud structure for all the IFO cases are summarized. The synoptic situations in which extensive cirriform clouds were observed are classified into three basic types: warm front cases, cold front cases, and closed low aloft cases. A simplified summary of each type of situation is presented.