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Evaluation of the boundary layer dynamics of the TM5 model over Europe

Koffi, E. N.; Bergamaschi, P.; Karstens, U. LU ; Krol, M.; Segers, A.; Schmidt, M.; Levin, I.; Vermeulen, A. T. LU ; Fisher, R. E. and Kazan, V., et al. (2016) In Geoscientific Model Development 9(9). p.3137-3160
Abstract

We evaluate the capability of the global atmospheric transport model TM5 to simulate the boundary layer dynamics and associated variability of trace gases close to the surface, using radon (222Rn). Focusing on the European scale, we compare the boundary layer height (BLH) in the TM5 model with observations from the National Oceanic and Atmospheric Admnistration (NOAA) Integrated Global Radiosonde Archive (IGRA) and also with ceilometer and lidar (light detection and ranging) BLH retrievals at two stations. Furthermore, we compare TM5 simulations of 222Rn activity concentrations, using a novel, process-based 222Rn flux map over Europe (Karstens et al., 2015), with harmonised 222Rn measurements... (More)

We evaluate the capability of the global atmospheric transport model TM5 to simulate the boundary layer dynamics and associated variability of trace gases close to the surface, using radon (222Rn). Focusing on the European scale, we compare the boundary layer height (BLH) in the TM5 model with observations from the National Oceanic and Atmospheric Admnistration (NOAA) Integrated Global Radiosonde Archive (IGRA) and also with ceilometer and lidar (light detection and ranging) BLH retrievals at two stations. Furthermore, we compare TM5 simulations of 222Rn activity concentrations, using a novel, process-based 222Rn flux map over Europe (Karstens et al., 2015), with harmonised 222Rn measurements at 10 stations. The TM5 model reproduces relatively well the daytime BLH (within 10-20% for most of the stations), except for coastal sites, for which differences are usually larger due to model representation errors. During night, however, TM5 overestimates the shallow nocturnal BLHs, especially for the very low observed BLHs (<100m) during summer. The 222Rn activity concentration simulations based on the new 222Rn flux map show significant improvements especially regarding the average seasonal variability, compared to simulations using constant 222Rn fluxes. Nevertheless, the (relative) differences between simulated and observed daytime minimum 222Rn activity concentrations are larger for several stations (on the order of 50%) than the (relative) differences between simulated and observed BLH at noon. Although the nocturnal BLH is often higher in the model than observed, simulated 222Rn nighttime maxima are actually larger at several continental stations. This counterintuitive behaviour points to potential deficiencies of TM5 to correctly simulate the vertical gradients within the nocturnal boundary layer, limitations of the 222Rn flux map, or issues related to the definition of the nocturnal BLH. At several stations the simulated decrease of 222Rn activity concentrations in the morning is faster than observed. In addition, simulated vertical 222Rn activity concentration gradients at Cabauw decrease faster than observations during the morning transition period, and are in general lower than observed gradients during daytime. Although these effects may be partially due to the slow response time of the radon detectors, they clearly point to too fast vertical mixing in the TM5 boundary layer during daytime. Furthermore, the capability of the TM5 model to simulate the diurnal BLH cycle is limited by the current coarse temporal resolution (3h/6h) of the TM5 input meteorology.

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published
subject
in
Geoscientific Model Development
volume
9
issue
9
pages
24 pages
publisher
Copernicus Gesellschaft Mbh
external identifiers
  • Scopus:84988000602
ISSN
1991-959X
DOI
10.5194/gmd-9-3137-2016
language
English
LU publication?
no
id
63d20c9e-ae28-4b93-9dd1-3d2255ac6df6
date added to LUP
2016-09-30 15:23:29
date last changed
2016-10-21 08:31:33
@misc{63d20c9e-ae28-4b93-9dd1-3d2255ac6df6,
  abstract     = {<p>We evaluate the capability of the global atmospheric transport model TM5 to simulate the boundary layer dynamics and associated variability of trace gases close to the surface, using radon (<sup>222</sup>Rn). Focusing on the European scale, we compare the boundary layer height (BLH) in the TM5 model with observations from the National Oceanic and Atmospheric Admnistration (NOAA) Integrated Global Radiosonde Archive (IGRA) and also with ceilometer and lidar (light detection and ranging) BLH retrievals at two stations. Furthermore, we compare TM5 simulations of <sup>222</sup>Rn activity concentrations, using a novel, process-based <sup>222</sup>Rn flux map over Europe (Karstens et al., 2015), with harmonised <sup>222</sup>Rn measurements at 10 stations. The TM5 model reproduces relatively well the daytime BLH (within 10-20% for most of the stations), except for coastal sites, for which differences are usually larger due to model representation errors. During night, however, TM5 overestimates the shallow nocturnal BLHs, especially for the very low observed BLHs (&amp;lt;100m) during summer. The <sup>222</sup>Rn activity concentration simulations based on the new <sup>222</sup>Rn flux map show significant improvements especially regarding the average seasonal variability, compared to simulations using constant <sup>222</sup>Rn fluxes. Nevertheless, the (relative) differences between simulated and observed daytime minimum <sup>222</sup>Rn activity concentrations are larger for several stations (on the order of 50%) than the (relative) differences between simulated and observed BLH at noon. Although the nocturnal BLH is often higher in the model than observed, simulated <sup>222</sup>Rn nighttime maxima are actually larger at several continental stations. This counterintuitive behaviour points to potential deficiencies of TM5 to correctly simulate the vertical gradients within the nocturnal boundary layer, limitations of the <sup>222</sup>Rn flux map, or issues related to the definition of the nocturnal BLH. At several stations the simulated decrease of <sup>222</sup>Rn activity concentrations in the morning is faster than observed. In addition, simulated vertical <sup>222</sup>Rn activity concentration gradients at Cabauw decrease faster than observations during the morning transition period, and are in general lower than observed gradients during daytime. Although these effects may be partially due to the slow response time of the radon detectors, they clearly point to too fast vertical mixing in the TM5 boundary layer during daytime. Furthermore, the capability of the TM5 model to simulate the diurnal BLH cycle is limited by the current coarse temporal resolution (3h/6h) of the TM5 input meteorology.</p>},
  author       = {Koffi, E. N. and Bergamaschi, P. and Karstens, U. and Krol, M. and Segers, A. and Schmidt, M. and Levin, I. and Vermeulen, A. T. and Fisher, R. E. and Kazan, V. and Klein Baltink, H. and Lowry, D. and Manca, G. and Meijer, H. A J and Moncrieff, J. and Pal, S. and Ramonet, M. and Scheeren, H. A. and Williams, A. G.},
  issn         = {1991-959X},
  language     = {eng},
  month        = {09},
  number       = {9},
  pages        = {3137--3160},
  publisher    = {ARRAY(0x993cc38)},
  series       = {Geoscientific Model Development},
  title        = {Evaluation of the boundary layer dynamics of the TM5 model over Europe},
  url          = {http://dx.doi.org/10.5194/gmd-9-3137-2016},
  volume       = {9},
  year         = {2016},
}