CompositesI

I will be showing composites of three different surge criteria:

(1) SAZ Zone IWVF above 90th ( 342 Total: 12 per Year: 3 per month)
(2) SAZ Zone IWVF above 90th for 2 consecutive days ( 146 Total: 5 per Year: 1.3 per month)
(3) All Zones IWVF above 90th ( 47 Total: 1.7 per year: 0.4 per month)

These criteria were chosen empirically, and simply based on which results I found interesting or best told a story.

All composites will be shown for 3 Days Before through 3 Days After an event.
====================================================================
First, let's look at plot (1)
I suppose my choosing this criteria was slightly less empirical than the other two simply because I felt as though looking at results for southern Arizona might provide some strong signals. The strongest signal composite appears to be between IWVF and precipitation. A clear northward flux of precipitation over the Great Basin can be seen to correlate temporally with Day -1 through Day +1. Precipitable Water values do appear larger during this same time period, but since the general spatial pattern of values for this parameter does not appear to be dynamic I am wondering if IWV results should be suspect. Having tried to use IWV in the past for defining surges and looking at other composites this issue has come up before. So, I believe that these values might be a little shifty in the model output. Again, there does seem to be a clear signal in the precipitation field in relation to these IWVF events.

====================================================================
Next, I wanted to look at events of two consecutive days of the above criteria. I felt that by further restricting my dataset, i.e., number of events, that I would get a clearer picture of patterns in the system.
Patterns here are very similar to what was seen in the previous composite. There is still a strong temporal agreement between IWVF and precipitation. Something I found interesting in this plot though is that on Day +1 there seems to be a more intense region of precipitation further north into southern Utah and Colorado. I believe that this is indicative a stronger surge event, which would agree with our criteria of needing two consecutive days to reach or exceed the 90th percentile in SAZ.

====================================================================
Finally, I looked at events of all three zones meeting or exceeding their 90th percentile on the same day. This criteria should allow us to look at the very strong surge events, and hopefully show us heightened signals compared to the previous two plots.
Indeed, we are seeing signals that one would suspect to be associated with strong surges of the NAM. Precipitation appears to be moving quite far northward now, and it also seems augmented compared to previous plots. At first, I felt as if my calculation might have been off based on the fact that precipitation seemed so heavy in Arizona for Day -1, and even Day -2. I don't believe this is an error, but is simply the first stages of the northward flux of moisture. If we looked at events for SAZ we would see that the majority of them are centered around Day -1 for this criteria, in place of the event day. This is shown in Figure 1 from 5 Sept 2009.

Again, the IWV values seem rather questionable. They do show some sign of being heigthened on Day -3 through Day -1, but I still have my reservations about trusting this data. One feature I have noticed in all plots is the elevated values of IWV in southeastern Arizona. I realized after looking at numerous plots that this region of elevated values of IWV is spatial correlated to a region of very low, for the region, precipitation values. This only makes me question this data more as I feel like this just does not make solid physical sense. The only connect I could make between the two is that the model is representing moisture that has not been precipitated out yet in this region. I am baffled.

You may have noticed that I left out dewpoint from this figures. Plots of dewpoint for all figures were ineffective at showing any association with the larger pattern or with IWVF events. I assumed, again, that my calculations were off, but after looking back through codes I found that dewpoint was calculated no different than any other parameter, and thus should not be showing signs of bad data manipulation. Once again, I am baffled.

I feel that the strong composites between IWVF and Precipitation is good, and expected, sign. This is showing that we are not only picking up events of IWVF, but that those events are associated with elevated precipitation patterns for the desert southwest. Seeing further northward progression of precipitation appear as we further restricted IWVF events to tougher criteria is also a good sign as it shows we are able to classify the stronger surges through IWVF values.

-jamie