Melting of snow flakes below freezing level in the atmosphere
Melting of snow flakes below freezing level in the atmosphere
复制标题
大气中雪花在冰点以下融化
DOI：
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发表时间：
1981
期刊：
影响因子：
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通讯作者：
Y. Sasyo
中科院分区：
文献类型：
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作者：
T. Matsuo;Y. Sasyo
本文从理论和观测两方面对大气中冰点以下的雪花融化现象进行了解释。理论方法的一个主要目的是研究空气相对湿度对雪花融化的影响，这是迄今为止从未提到过的。它是基于这样的考虑，即除了由于从环境空气到雪花的热扩散引起的热传递之外，伴随着来自雪花表面或在雪花表面上的水蒸气的升华或冷凝的潜热对雪花的融化速率施加显著的影响。在理论计算中，我们使用了以前由Matsuo和Sasyo（1981）提出的雪花融化速率的经验公式作为基本方程。雪花直径，液态水含量，和下降速度的函数的距离低于冻结水平，通过使用参数，如空气的相对湿度，雪花的大小和密度的计算。在冰点以下的饱和空气中，雪花从冰点以下开始融化，雨滴中等效直径为1-5 mm的雪花在数百米内完全融化。这样形成的熔化层的宽度随着所含雪花的尺寸和密度的增加而增加。另一方面，在冰点以下的亚饱和空气中，由于水蒸气升华使雪花冷却，所以在冰点以下相当远的距离处雪花不会融化。这样形成的非熔化层的宽度随着相对湿度的降低而几乎线性地增加;例如，相对湿度为90%时约为120 m，RH= 50%时约为700 m。在非融化层下，由于空气温度和水蒸气密度的增加，来自环境空气的热传递增加，雪花开始融化。熔融层的宽度随着层变得干燥而减小。随着距冻结面以下距离的增加，非融化层中的雪花下落速度略有减小，融化层中的雪花下落速度迅速增大。在观察中，同时测量了雪花的含水量、下落速度、质量和横截面积。观测结果表明，雪花的下落速度和液态水含量与其质量的函数关系取决于0 * 以上的地面气温和相对湿度。特别是在高表面空气温度（*1*），下降速度几乎是恒定的，相对于他们的质量和他们中的一些在小质量范围内高于那些在大质量范围。这一发现表明了与Magono（1953）和Langleben（1954）观察到的结果不同的趋势。理论计算很好地解释了这些观测结果。
A theoretical and observational approach was made to elucidate the phenomena of melting of snowflakes below freezing level in the atmosphere. A main purpose of the theoretical approach was to examine the effect of relative humidity of air on snowflake melting that has never referred so far. It is based on the consideration that latent heat accompanied with sublimation or condensation of water vapor from or on snowflake surface exerts a significant influence on the melting rate of snowflakes in addition to heat transfer due to heat diffusion from the ambient air to snowflakes. In the theoretical calculations, we used an empirical formula of the melting rate of snowflakes proposed previously by Matsuo and Sasyo (1981) as the basic equation. Snowflake diameter, liquid water content, and fall velocity as a function of distance below freezing level were obtained by the calculations using parameters such as relative humidity of air, snowflake sizes, and densities. In saturated air below freezing level, snowflakes commenced melting from just below freezing level and snowflakes with equivalent diameter 1-5 mm in raindrops completed melting within several hundred meters. The width of the melting layer thus formed increased with increasing sizes and densities of snowflakes contained. In subsaturated air below freezing level, on the other hand, melting of snowflakes did not take place as far as a considerable distance below freezing level because of cooling of snowflakes by sublimation of water vapor. The width of the non-melting layer thus formed increased nearly linearly as relative humidity decreased; for example, it was about 120 m for relative humidity of 90%, and 700 m for RH=50%. Under the non-melting layer, snowflakes commenced melting because of increase in heat transfer from the ambient air due to increase in air temperature and water vapor density. The width of the melting layer decreased as the layer became dryer. Fall velocity of snowflakes decreased slightly in the non-melting layer and increased rapidly in the melting layer with increasing distance below freezing level. In the observations, simultaneous measurements were carried out for snowflake water content, fall velocity, mass, and cross-sectional area. The observational results showed that fall velocity and liquid water content of snowflakes as a function of their mass were dependent on surface air temperature above 0 * and relative humidity. Especially at high surface air temperature (*1*), fall velocities were almost constant with respect to their masses and some of them in small mass range were higher than those in larger mass range. This finding shows a different tendency from the results observed by Magono (1953) and Langleben (1954). These observational results were interpreted well by the present theoretical calculations.