UKCA Chemistry and Aerosol Tutorial 10

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What you will learn in this Tutorial

In this tutorial you will learn about the GLOMAP-mode aerosol module and how it tracks different aerosol types within several size classes. You will understand the standard configuration used in the UKCA jobs so far whereby the mass mixing ratios of sulphate, sea-salt, black carbon and organic matter in each mode are transported via separate tracers. GLOMAP-mode is an aerosol microphysics scheme and therefore, as well as transporting the mass of several components in the modes, the scheme also transports the number concentrations of particles in each mode.

The lecture given on Monday morning already introduced the basic concepts behind the GLOMAP-mode aerosol microphysics scheme.

GLOMAP-mode has been coded to enable several supported "aerosol configurations" to be run within UM-UKCA using the same code-base.

Initially developed in the TOMCAT CTM environment (see Manktelow et al., 2007; Mann et al., 2010; Mann et al., 2012), the GLOMAP code then became the aerosol module for the UKCA sub-model of the UM (see Bellouin et al., 2013; Kipling et al., 2014; West et al., 2014; Dhomse et al., 2014; Mann et al., 2014).

GLOMAP is now also implemented into the ECMWF Integrated Forecasting System as part of the "Composition IFS" module (C-IFS) where it will be used in combination with data assimilation of satellite Aerosol Optical Depth to provide forecasts and re-analyses of atmospheric composition and boundary conditions for regional air quality models.

In section 12 of the UKCA UMDP, Table 18 shows the standard configuration for GLOMAP in all 3 of these modelling frameworks (TOMCAT, UM-UKCA and C-IFS-GLOMAP).

There the model runs with 7 modes each containing mixtures of up to 5 different aerosol components (sulphate, black carbon, organic matter, sea-salt and dust). In the configuration one has 7 number mixing ratios (one for each mode) and a total of 19 component mass mixing ratios (known as setup 8).

The main currently supported configuration of GLOMAP within UM-UKCA has GLOMAP used in "5-mode configuration" (known as setup 2) covering only 4 of the above 5 components (sulphate, black carbon, organic matter and sea-salt) with dust handled via the existing 6-bin UM dust scheme.

The scheme can be reduced to cover just the sulphate and sea-salt components in 4 modes (known as setup 1) or extended to track two separate components for organic matter (OM) to track the mass of primary OM and secondary OM in each mode.

Section 12.2 of the UMDP has a more detailed explaination of these components with Table 19 showing how these 4 different configurations map onto the model tracers.

In this task you will take a copy of the standard UKCA job (which uses setup 2, MS2) and change it to use GLOMAP-mode "setup 4 (MS4) to track two separate organic matter (OM) components rather than the usual 1. With the 2-component OC configuration, the model tracks primary (emitted) organic carbon in the and secondary organic matter (formed following oxidation in the atmosphere) separately.

Task 10.1: Understand how the GLOMAP aerosol module tracks aerosol species and modes

TASK 10.1: Read section 12 (page 32) of the v8.4 UM Documentation Paper and refer to Tables 18, 19 and 20 on pages 33, 34 and 35.

Task 10.2: Run a copy of the standard UKCA job which tracks two OC components in the GLOMAP modes

Take a copy of the xjluc (owner gmann) job from the UMUI and change the settings to be run by you. This xjluc is identical to the 2-day UKCA tutorial job from the earlier exercises but uses the 2-component OC GLOMAP configuration. The job xjlub is the UKCA tutorial job with the standard GLOMAP configuration.

Task 10.3 Examine the simulated total organic carbon in the original and two-cpt OC configurations

Once your standard and 2-component OC UM-UKCA jobs have completed you can plot up the output.

We recommend you use xconv for this task although you may prefer to use IDL.----

In these xjlub and xjluc jobs additionally daily-mean fields have been requested from STASH.

Included in the extra STASH requests are the mass mixing ratios of OC (the standard organic component) and SO (the 2nd organic component) in each mode.

The OC mmrs are STASH section 34, items 126 (nucleation mode), 106 (Aitken-soluble), 110 (accumn-soluble), 116 (coarse-soluble) and 121 (Aitken-insoluble).

The SO mmrs are STASH section 34, items 128 (nucleation mode), 129 (Aitken-soluble), 130 (accumn-soluble), 131 (coarse-soluble).

These STASH item numbers and the details of the standard and 2-component GLOMAP configurations can be found in the UKCA UMDP section 12 Tables 19 and 20.

Note that there is no SO in the Aitken-insoluble mode as this contains only primary carbonaceous particles. Any SO or OC condensing onto the particles in the insoluble modes is immediately transferred over to the corresponding soluble mode following the "condensation-ageing" approach used by the model. This OC or SO condensing onto the insoluble particles is a kind of "coating" for the particles making the particles hygroscopic/soluble.

The mmr of the gas phase species MONOTER and SEC_ORG (STASH section 34, items 91 and 92) are also requested.

As an example I have attached here a . pdf which compares surface fields between xjlub (top-left) and xjluc (top-right).

Included in these plots are the "total POM mmr" which is the total particulate organic matter (POM) summing up the mass of OC and SO in each mode.

There also are pages showing comparisons of "total POM1 mmr" and "total POM2 mmr" which are the sum of the 1st and 2nd organic component over all the modes.

You can see from the example that the "total POM2 mmr" in xjlub is zero everywhere. That's because in this job GLOMAP has the standard configuration with just one organic component.

By contrast the "total POM2 mmr" for xjluc has considerable concentrations in vegetated continental regions. In this "I_MODE_SETUP=4" configuration, the "SEC_ORG" species (which contains the secondary organics from monoterpene oxidation) condenses into the "SO" component, whereas in xjlub SEC_ORG condenses into the "OC" component.

This task illustrates how one can separate out the aerosol mass from different sources and track them separately via a different aerosol component.

One could also introduce a 2nd gas phase species like "SEC_ORG" to track different types of SOA. For example one could configure the model so that such a 2nd "SEC_ORG2" species held semi-volatile oxidised organic species with very low volatile oxidised organics held in the usual "SEC_ORG" species.

Written by Graham Mann 2014