Evening, Feb. 1

I've been working on understanding fortran code that Steve wrote to calculate the cloud work function and associated minimum entrainment rates after Moorthi and Suarez 1992. After perhaps 3 days of work, I have it working in Matlab in a very generalized way so that changing just a few variables in one place will consistently work through the rest of the code. GIGA-LES profiles are automatically read in from the stats file for any choice of times, a variable number of layers at the bottom of the profile can be averaged together to represent an idealized mixed layer, etc. I was able to reduce the loop run time from 20 seconds per loop down to about 0.25 s, so I can see the results of changing a few parameters over the 290 time loops in seconds instead of more than an hour.

However... what has this gotten me? Curious figures with mysterious gaps... what do they represent, how can they help answer the research question? Below is a plot of the calculated normalized entrainment rate. The full matrix actually has values over the whole domain, but some are negative, and a negative entrainment rate doesn't make physical sense in the context of the RAS model. Furthermore, just to see detail in the regions, I took the base 10 log of all values before mapping to color because the highest values (which surround the blank negative regions) are enormously higher than elsewhere. The highest values immediately transition to negative values, which to me screams of a calculation error.

There are several things to see in the plot, however. First in the circled region note that at a level, over time, a larger and larger minimum entrainment rate allows a parcel to reach that height as its non-buoyancy level (NBL). This illustrates the shifting of the already unstable profiles to be more and more unstable. At about 6 hours in we see the peak that coincides with the observed transition to deep, over-shooting convection with heavy precipitation. In the square region the values are quasi-constant, illustrating that the transition to quasi-equilibrium of the cloud work function has occurred.

Yesterday Steve and I both confirmed we had thought of a physical way to consider the blank regions, his was simpler and more intuitive: Consider a valley or depression like a crater with a peak or bump in the middle. A ball rolled from the edge may travel a variable distance up to the other crater wall depending on variable forces like friction, etc. However, if passing the hill in the center of the crater, it will either make it up and over this obstacle, or roll back and settle at the foot of the hill. There could never be a ball reaching an equilibrium level on the slope of the middle hill. In the same way, if there is a "bump" in the saturation moist static energy profile, given certain initial conditions, no parcel may come to a NBL within that region, but above or below it might be possible from a calculation view. However, the sat. MSE profile really has no serious "bump" to explain the region.

Why does the blank space shrink after the transition time (marked with arrows)? This is approximately the time precipitation is evaporating in those levels. I feel very close to mastery of the code and understanding where the error is coming from. But even if I could, is it a good use of time moving forward? Will it help with understanding what it is that allows the transition to deep convection? I think it is at least worth a few more hours. Once I can confirm the code is working properly I can move forward with our Giga-LES analysis plan and decompose the changes in the CWF into parts due to cumulus and due to the large scale forcing. Depending on the timing of changes caused by each part, it may be one step closer to understanding why deep convection doesn't take off in the simulation right away.