| OCR Text |
Show Introducing the numerical values for the above constants yields: s- o. 75'/ g- 2 p£ ff / j p T R ^ a ^ C ^ ^ c l a u ^ ( 19) 2L/. 5 ' J With the mass flux approximated in terms of quantities measurable in the field, we next estimate the time required for depth hoar crystals of given size to form from this vapor supply. Assume a layer of depth hoar crystals equal in thickness to the average crystal size, d ( centimeters), has formed from sublimation of this vapor supply. The amount of mass required can be calculated if the density of this layer is known. Field observations fortunately furnish a basis for estimating this density. Time profile records over several years at Berthoud Pass, Colorado, where depth hoar formation is common, show that such layers commonly approach a bulk density of 0.25 to 0.30 as this crystal type becomes fully developed. ( See Report F- l). We adopt here a mean bulk density of 0.28 for the purpose of computation. The time required to form this layer of thickness is d is then given by •£,= O-^ feoL ^--. 37cjp^ A , T C y \ j s |
