求助一段积雪变质物理过程方面的英文文献段落的翻译

求助一段积雪变质物理过程方面的英文文献段落的翻译
A new snowfall occurred on December 18 followed by a clear night, and on December 19 the snowpack, 32 cm deep, was composed of surface hoar (E = 3.0 mm) overlaying a layer of fresh snow 6 cm deep, formed by decomposed precipitation particles and rounded particles (E = 0.3 mm), as well as a crust due to refreezing of the previously melted layer and other layers with faceted crystals (in some cases rounded particles with few faceted, E = 0.5 mm), and some rounded polycrystals caused by the heating of snowpack on December 17. The crust was the result of the strong nocturnal irradiation.
疑惑如下：
1. surface hoar (E = 3.0 mm)是formed by decomposed precipitation particles and rounded particles (E = 0.3 mm)?
2. the snowpack, 32 cm deep,是由 surface hoar (E = 3.0 mm) 、a crust 和some rounded polycrystals 组成的吗?
3. 最后一句“The crust was the result of the strong nocturnal irradiation.”不知怎么理解,文章前后貌似没有讲什么是nocturnal irradiation.