Bioprecipitation, the concept of rain-making bacteria, was proposed by David Sands from Montana State University. Such microbes – called ice nucleators – are found in rain, snow, HP Pavilion dm4-1008tu Battery and hail throughout the world. These bacteria may be part of a constant feedback between terrestrial ecosystems and clouds and may even have evolved the ability to promote rainstorms as a means of dispersal. They may rely on the rainfall to spread to new habitats, much as some plants rely on windblown pollen grainsHP Pavilion dm4-1008tx Battery.
Howard’s original system established three general cloud categories based on physical appearance and process of formation: HP G62-120SW Batterycirriform (mainly detached and wispy), cumuliform or convective (mostly detached and heaped, rolled, or rippled), and non-convective stratiform (mainly continuous layers in sheets). These were cross-classified into lower and upper families. Cumuliform clouds forming in the lower level were given the genus name cumulus, HP G62-121EE Battery and low stratiform clouds the genus name stratus. Physically similar clouds forming in the upper height range were given the genus names cirrocumulus (generally showing more limited convective activity than low level cumulus) and cirrostratus, respectively. HP G62-125EK BatteryCirriform category clouds were identified as always upper level and given the genus name cirrus. To these, Howard added the genus nimbus for all clouds producing significant precipitation.
Around 1840–41, HP G62-125EL Battery German meteorologist Ludwig Kaemtz added stratocumulus as a mostly detached low-cloud genus of limited convection with both cumuliform and stratiform characteristics, similar to upper level cirrocumulus. About fifteen years later, HP G62-125EV Battery Emilien Renou, director of the Parc Saint-Maur and Montsouris observatories, began work on an elaboration of Howard’s classifications that would lead to the introduction of altocumulus (physically more closely related to stratocumulus than to cumulus) and altostratus during the 1870s. These were cumuliform (of limited convection) and stratiform cloud genera, HP G62-125SL Batteryrespectively, of a newly defined middle height range above stratocumulus and stratus but below cirrocumulus and cirrostratus, with free convective cumulus and non-convective nimbus occupying more than one altitude range as clouds with vertical extent. In 1880, HP G62-130 BatteryPhilip Weilbach, secretary and librarian at the Art Academy in Copenhagen, and like Luke Howard, an amateur meteorologist, proposed and had accepted by the International Meteorological Committee (IMC) the designation of a new free-convective vertical genus type, cumulonimbus, HP G62-130EG Batterywhich would be distinct from cumulus and nimbus and identifiable by its appearance and ability to produce thunder. With this addition, a canon of ten cloud genera was established that came to be officially and universally accepted. At about the same time, several cloud specialists proposed variations that came to be accepted as species subdivisions and varieties determined by more specific variable aspects of the structure of each genus. HP G62-130EK Battery One further modification of the genus classification system came when an IMC commission for the study of clouds put forward a refined and more restricted definition of the genus nimbus renamed nimbostratus.