SOL/INSOL fixes: Secondary organics bug fix and improved hygroscopicity #29
Description
This issue aims to address two small issues and bugs within the SOL/INSOL (mode setup 11) design.
Due to the fact that SOL/INSOL treats all soluble aerosol as sulphate, we have a bug where secondary organics aren't condensing onto the aerosol population, due to the lack of organic carbon aerosol in this set up. Some steps had been taken already to include this process by changing the condensable_choice array within SOL/INSOL to be 1 - matching the sulphate indice. This failed to account for the way the routine ukca_conden works to condense gases onto aerosol species and this bug fix ensures, in the case of SOL/INSOL, that secondary organics condense onto sulphate aerosol in this routine.
The second SOL/INSOL fix we are including in this issue is to add a tunable parameter for the redistribution of aerosol into its 4 main species within the hygroscopicity routine. Aerosol grows due to its hygroscopicity and if we treat all aerosol as sulphate, we see a much faster growth than if we treat it as it the different species we know it is, as organic/black carbon aerosol is more hydrophobic and grow slower. This isn't an issue over certain domains where sulphate is the dominant species but over the Amazon domain, for example, we see AOD grow significantly within even one hour from initialisation. This fix will include adding a namelist item, and so will need a link to a UM issue and PR, and will allow users to tune the ratio of aerosol species, allowing for improved aerosol growth in areas where sulphate isn't dominant.
This issue is linked to MetOffice/um#58