Dependence of Snowfall on Temperature
D'OOGE has reported1 a correlation between amount of snowfall in inches and temperature at the time of snowfall. His data showed that maximum depth of snowfall occurred at a daily mean temperature of − 11° C. ; Bossolasco2 correlated frequency of occurrence of snowfall with temperature and found maximum occurrence at approximately the same temperature. These observers assumed that the mean daily temperature recorded at the level of observation was a reasonable estimate of the temperature at the level of formation of the snow. From the data presented, conclusions were drawn concerning nucleation of snow crystals.
Snowfall and Temperature on a California Mountain
A SNOWFALL and temperature analysis has been completed for six winter seasons (1948–54) on White Mountain, California (elevation 10,600 ft.). Snowfall and the temperature maxima and minima were measured for every 24 hr. at 0800 Pacific Standard Time. Fig. 1a shows the total snowfall as a function of the mean air temperature of the day on which the snow fell. An interesting peak occurs at − 11 ° C., just as Bossolasco reports1 for the case of snowfall at Weissfluhjoch. Rau's laboratory work2 indicates that the majority of atmospheric nuclei induce freezing between − 10° and − 12° C. Silver iodide begins its activity as a freezing nucleus in the laboratory at − 4° C. 3, and at this point Fig.1a shows another peak. Bossolasco has also mentioned that Mason and Ludlam4 report this point as a secondary maximum in laboratory frequency of atmospheric freezing nuclei. However, it is believed that the − 4° C. peak may be related to large cloud-seeding experiments utilizing silver iodide smoke carried on in the Sierra Nevada Mountains about thirty miles up wind to the west5 during the seasons 1951, 1952 and 1953. Vonnegut6 expected that unusual and far-reaching effects must be expected in the case of such seedings, since silver iodide is much more active than any known natural ice nucleus.
Palaeomicrobiology: current issues and perspectives
Palaeomicrobiology is an emerging field that is devoted to the detection, identification and characterization of microorganisms in ancient remains. Data indicate that host-associated microbial DNA can survive for almost 20,000 years, and environmental bacterial DNA preserved in permafrost samples has been dated to 400,000–600,000 years. In addition to frozen and mummified soft tissues, bone and dental pulp can also be used to search for microbial pathogens. Various techniques, including microscopy and immunodetection, can be used in palaeomicrobiology, but most data have been obtained using PCR-based molecular techniques. Infections caused by bacteria, viruses and parasites have all been diagnosed using palaeomicrobiological techniques. Additionally, molecular typing of ancient pathogens could help to reconstruct the epidemiology of past epidemics and could feed into current models of emerging infections, therefore contributing to the development of appropriate preventative measures.