Fire affects on storm development

[Jason Foster]

Looking at the forecasts for 3/30/08 and then browsing SPC, was wondering if a wildfire that was burning in AZ or NM, upwind of the storms potential, would the particulate from the storms affect storm development enough to mean anything? Just something I never thought of before.

Tomorrow's set up brought up the question, but isn't particular to tomorrow's set, just a general question.

 

[Aaron Kennedy]

Jason, wildfires could impact storms by increasing the number of cloud condensation nuclei available. The most notable impact occurs between maritime and continental clouds and raindrop size distributions. Over water, there are fewer CCN, so you end up with fewer, larger drops in a narrow distribution.

In continental areas where dust, pollution, wildfires, etc. are common, you end up a distribution with a wide spread of drop sizes.

The change in CCN from aerosols can be extremely important in determining the lifetime and radiative properties of marine low-level clouds. It is well known that clouds in areas of pollution are more reflective (direct effect). There is also evidence that they persist longer (indirect effect). These have implications for climate change, and is one big mysteries in our climate models... the aerosol forcing.

So what about for thunderstorms? I don't have the references handy, but from what I read, changes in CCN over land had minimal impact on updrafts (these were tropical, in a low-shear environment) . I would hypothesize that there may be important microphysical impacts early on in the cloud's lifetime, but given the large number of collisions in a convective updraft, the dynamics take over pretty quickly. I'm unaware of any studies that have investigated the changes of aerosols in model runs of supercells. Implementation of aerosols in these models is pretty rudimentary.