A Mesoscale Model of the Planetary Boundary Layer Over the Ocean

那些熟悉加利福尼亚海岸天气的人可以证明云量的变化。有时一层平流层积云可以持续数百英里数小时或数天。在其他时候，这样一层云可能在相对较短的时间内形成和消散。云顶夹带不稳定性是层积云甲板分裂成分散积云的机制。人们普遍认为，该过程的开始取决于温度和混合比在反演上的不连续。即当等效电位温度差小于某一临界值时，反转是不稳定的，夹带可以自由发生。然而，最近的证据表明，尽管这种不稳定，云甲板可能仍然稳固。这需要其他机制维持夹带不稳定性；一些例子包括云层内的湍流，云和次云层之间的耦合，以及剪切引起的夹带。在这项资助下，大卫·罗杰斯博士将利用海洋上方行星边界层的中尺度模型研究这些物理机制。这些结果将增加我们对海洋层积云演化的认识。

Those familiar with the weather off the California coast can attest to the variability of cloudiness. Sometimes a deck of strato-cumulus clouds may persist for hundreds of miles for hours or days. At other times such a layer of clouds may form and break up within a relatively short period of time. Cloud-top entrainment instability is the mechanism whereby a stratocumulus deck breaks up into scattered cumulus clouds. It is generally accepted that the onset of the process depends on the temperature and mixing ratio discontinuity across the inversion. That is, whenever the equivalent potential temperature difference is smaller than a critical value, the inversion is unstable and entrainment can occur freely. However, recent evidence suggests that despite this instability the cloud deck may remain solid. This requires that other mechanisms sustain the entrainment instability; some examples include turbulence within the cloud layer, coupling between the cloud and subcloud layers, and shear induced entrainment. Under this grant, Dr. David Rogers will study these physical mechanisms using a mesoscale model of the planetary boundary layer over the ocean. The results should increase our understanding of the evolution of marine stratocumulus.