Controlling UKCA tracers from vn9.0

INCOMPLETE DRAFT

Up to and including UM version 8.6, tracers were controlled by setting values in a 150 element array tc_ukca in the SIZES file. The UMUI set this up for existing chemistry schemes but for new chemistry schemes or if you wish to add/remove tracers from an existing scheme, a hand edit is needed. With the introduction of Rose, it was no longer possible to generate the tc_ukca in the GUI and a different approach was needed. This page explains the new approach.

Option codes - an introduction

In the STASHmaster_A file, for every variable there is a 30 digit number known as the option code. For example take stash item 0.152, River direction.

1|    1 |    0 |  152 |RIVER DIRECTION                     |
2|    3 |    0 |    1 |   23 |    5 |   -1 |   -1 |    0 |    0 |    0 |    0 |
3| 000000000000300000000000000000 | 00000000000000000001 |    3 |
4|    1 |    2 | -99  -99  -99  -99  -99  -99  -99  -99  -99  -99 |
5|    0 | 1906 |    0 |  129 |    0 |    0 |    0 | 9999 |  000 |

The option code is in line 3 of this record. The option code numbers are labelled from right to left as n30n29....n2n1. In the above record all option code entries are zero except n18 which is 3. This means that this option is only available if the river routing scheme is used. For a full list of option codes see Appendix C "STASHmaster File Definition" in UMDP C4 "Storage Handling And Diagnostic System (STASH)" from http://collab.metoffice.gov.uk/twiki/bin/view/Support/Umdp

If an opion code is all zeros then it is always ON. It is important to note that the option codes can have different meanings for each section of the UM.

How UKCA option codes control which tracers are on

The routine which controls which UKCA tracers are on is in the UKCA subdirectory and called tstmsk_ukca.F90. The purpose of this subroutine is to return a logical value which is true if the tracer is on and false if it is off.