 |
| Titel |
Evaluating the Met Office Unified Model simulated land surface temperature (LST) using a multi-platform approach |
| VerfasserIn |
Jennifer Brooke, Chawn Harlow, Martin Best, Stuart Newman, Russell Scott, John Edwards, Jean-Claude Thelen, Ed Pavelin, Mark Weeks |
| Konferenz |
EGU General Assembly 2015
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103367
|
| Publikation (Nr.) |
 EGU/EGU2015-4826.pdf |
|
|
|
|
|
| Zusammenfassung |
| The Met Office Unified Model (UM) has a significant cold bias in land surface temperature
(LST) in semi-arid regions at global resolution, and limited area 4.4 km and 2.2 km
configurations. The daytime LST cold bias simulated by the JULES land surface scheme
within the UM is present throughout the annual cycle in semi-arid regions of the globe
in comparison to IASI retrievals. These errors are largest in late spring and early
summer and have magnitudes of 5 to 15 K, dependent on model resolution. This work
will show verification of model biases through ground-based, in-situ airborne and
satellite observations during the Semi-Arid Land Surface Temperature and IASI
Calibration Experiment (SALSTICE) in semi-arid south-eastern Arizona in May
2013.
Airborne observations of LST from the FAAM research aircraft using the Airborne
Research Interferometer Evaluation System (ARIES) were used to investigate the spatial
distribution of the model errors and evaluate IASI retrievals. Airborne retrievals of surface
temperature were found to broadly agree with IASI retrievals; uncertainties are
attributed to the spatial variability in the ARIES measurements compared with
the IASI footprints and due to differences within the retrieval, such as assumed
emissivity. The UM errors in LST were found to vary with model resolution as well as
topographic complexity, with the coarse resolution global model having larger errors
than the limited area models. Regions with complex terrain had the highest LST
errors while the errors over the less complex basins were lower, in the range of 4-5
K.
Evaluation of the JULES land surface scheme has been performed for flux tower sites in
the Walnut Gulch Experimental Watershed in south-eastern Arizona. An annual dataset of
flux tower measurements confirms the LST biases seen with aircraft and satellite observations
and indicates that night-time LST biases are of the order of those observed during the day.
Comparisons of different model resolutions show the night time bias is largest in the 2.2 km
model resolution (6.5 K) compared with the global 25 km model (3 K). Verification of this
diurnal pattern in LST biases with model resolution has been achieved using MODIS
retrievals.
Flux tower measurements have shown that JULES simulated turbulent heat fluxes are
larger compared with observations (21 W m-2, monthly average) and ground heat
fluxes too small (3.5 W m-2, monthly average). The accurate representation of
bare soil vegetation fraction in JULES simulations is shown to be of particular
importance, reducing biases in the sensible heat flux (16 W m-2, monthly average). |
|
|
|
|
|
|