Opened 5 months ago

Last modified 2 months ago

#2543 assigned defect

vegetation Leaf Area Index (LAI) for each Plant Functional Type (PFT): December anomaly

Reported by: pmcguire Owned by: pmcguire
Priority: normal Component: Land Surface Modelling
Keywords: LA, Leaf Area Index, ancillary, PFT, Plant Functional Type, MODIS, December anomaly Cc: d.hertwig@…
Platform: UM Version:

Description

Denise Hertwig and Sue Grimmond reported that the standard veg.func ancillary file for Leaf Area Index (LAI) shows anomalously high values in December in southern England. One might expect the LAI to be high in the summer and low in the winter. The ancillary file shows LAI values that are high in the summer and then going down in the fall, prior to a second large enhancement in LAI in December. They report this for the PRIMAVERA HadGEM3 (coupled) ancillary file.

See the attached files from Denise.

With my suggestion, they have verified this December anomaly over much of Europe by comparing the November LAI with the December LAI with ncview.

The JULES standalone ancillary file for veg.func has header information that says that Heather Ashton (now Rumbold) created the ancillary in 2017. I found her 2009 PhD dissertation/thesis on JULES related topics, wherein in Figs 3.11-3.12 she shows plots of the seasonal variation of the MODIS-derived LAI over southern England and over France. These plots show similar December anomalies to those that Denise and Sue have observed.
Her thesis is at:
http://www.met.rdg.ac.uk/~bl_met/research/PhDtheses/Ashton_2009.pdf
She describes the procedure that she used in 2009 to make LAI for each Plant Functional Type (PFT). This PFT-dependent LAI is derived from the PFT-independent MODIS measurements of LAI by 'green-ness', weighting for each PFT by fixed abundance.

Attachments (3)

LAI_single_gridbox.png (181.2 KB) - added by pmcguire 5 months ago.
LAI_monthly_BT.png (211.9 KB) - added by pmcguire 5 months ago.
LAI_monthly_C3.png (214.1 KB) - added by pmcguire 5 months ago.

Download all attachments as: .zip

Change History (5)

Changed 5 months ago by pmcguire

Changed 5 months ago by pmcguire

Changed 5 months ago by pmcguire

comment:1 Changed 5 months ago by pmcguire

  • Status changed from new to assigned

comment:2 Changed 2 months ago by pmcguire

We're continuing to work on this.
I was able to get the original MODIS Leaf Area Index (LAI) data (provided by Boston University) from Samantha Pullen at the Met Office, as well as IDL reading routines. I was able to compare the November and December data for each of the years 2005-2009 in this source data for MODIS. The anomaly in December does seem to be present in that dataset in southern England.

George Meachim was able to compare a more recently-created version of this 2005-2009 MODIS LAI data (provided by GLASS?) for the different months of the year, and the anomaly does not seem to be there for December in southern England.

Maybe we need to update the data source?

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