TCOR-CH4: Daily global 3-D stratospheric methane profile dataset constructed using TOMCAT CTM, Occultation measurements and Random Forest.

These are 31-data files  (1 per calendar year)  containing daily 3D global methane profile data set. Vertical profiles are available at 1 km vertical resolution (10km-60km) for 1991-2021 time period at 128 X 64 degree horizontal resolution (12 UTC).  The data set are constructed using methane profiles from TOMCAT CTM that are corrected using Random Forest w.r.t. vertical profiles measurements from two solar occultation instruments (HALOE [1991-2005] and ACE [2004-2021]).

Methodology:  TOMCAT simulation is performed at T64L32 resolution that is similar to the one used in Dhomse et al., (2021, 2022) for 1991-2021 time period. Collocated methane profiles are divided in five latitude bins: SH polar (90S-60S), SH mid-lat (60S-30S), tropics (30S-30N), NH mid-lat (30N-60N) and NH polar (60N-90N). Initially, differences are calculated for each zonal bins for 51 height levels (10km to 60km). Then separate Random Forest regression models are trained for the methane differences between TOMCAT and measurements at each level for a given latitude bin. Same model is used for all 11323 days for TOMCAT output at 12 UTC to get bias corrections for a given model grid that are added to the original TOMCAT profiles. Note that there are fewer occultation measurements below tropopause, hence TCOR profiles below tropopause are not well constrained.

Dataset also includes two  additional files:

 ch4-monthly-TCOR-19910101-2021231.nc – monthly mean fields (3D)

zmch4-daily-TCOR-19910101-2021231.nc – zonal mean daily  fields

We are not sure about exact cause of unusual methane variations during 1991-1994, but some recent studies argue that it could be due to sudden changes in methane loss processes following Mount Pinatubo eruption as well as significant changes in methane emissions following collapse of soviet union.