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

Abstract

We evaluate the capability of the global atmospheric transport model TM5 to reproduce observations of the boundary layer dynamics and the associated variability of trace gases close to the surface, using radon (222Rn), which is an excellent tracer for vertical mixing owing to its short lifetime (half-life) of 3.82 days. Focusing on the European scale, we compare the boundary layer height (BLH) in the TM5 model with observations from the NOAA Integrated Global Radiosonde Archive (IGRA) and in addition with ceilometer measurements at Cabauw (The Netherlands) and lidar BLH retrievals at Trainou (France). Furthermore, we compare TM5 simulations of 222Rn activity concentrations, using a novel, process-based 222Rn flux map over Europe (Karstens et al., 2015), with quasi-continuous 222Rn measurements from 10 European monitoring 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, TM5 overestimates the shallow nocturnal BLHs, especially for the very low observed BLHs (< 100 m) 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 %) compared to 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 larger at several continental stations, which 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, which points 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 due to the current coarse temporal resolution (3 hr/6 hr) of the TM5 input meteorology. Additionally, we analyze the impact of a new treatment of convection in TM5, based on the ECMWF reanalysis, leading to overall significantly lower (on the order of ~ 20 %) surface 222Rn activity concentrations during daytime compared to the current default convection scheme based on Tiedtke (1989). However, the performance of the model simulations compared to the 222Rn observations is very similar in terms of root mean square and correlation coefficient ...

Inverse modelling of European CH&lt;sub&gt;4&lt;/sub&gt; emissions during 2006–2012 using different inverse models and reassessed atmospheric observations

“…In contrast, pronounced enhancements in measured and simulated CH 4 compared to the background are apparent at the other three sites, especially in the lower ∼ 2 km due to regional emissions. These enhancements show some seasonal variation, with largest vertical extension during summer (∼ 2 km), while they are confined to the lower ∼ 1 km during winter due to the seasonal variations in the average boundary layer height (Koffi et al, 2016). Please note that the differences in the background mole fractions, which are visible in Fig.…”

“…A recent comparison of the TM5 BLH with observations from the NOAA Integrated Global Radiosonde Archive (IGRA) (Koffi et al, 2016) showed that TM5 reproduces the daytime BLH relatively well (within ∼ 10-20 %), but larger deviations were found for the nocturnal BLH, especially during summer, when very low BLHs (< 100 m) are observed. Here, we use only profiles for which the (TM5 diagnosed) BLH is not lower than 500 m. The average enhancement of the measurements and model simulations in the boundary layer compared to the background is denoted by c OBS, BL and c MOD, BL , respectively (further details about the evaluation of the enhancements are given in the Supplement).…”

On the Potential of 25 Years (1991–2015) of Rawinsonde Measurements for Elucidating Climatological and Spatiotemporal Patterns of Afternoon Boundary Layer Depths over the Contiguous US

“…The extent to which NARR can simulate the features of PBL depth seasonal cycles over different sites characterized by various climate types observed in Figures 11 and 12 will provide new findings on the skill of reanalysis products. Thus, it will be possible to address in detail the effects of changes in land surface forcing over diverse geographical regions, as was recently performed by [42] for Europe using Transport Model 5 (TM5). Also, the analyses will be extended for the >200 IGRA sites located along coasts around the world to further investigate the impact of marine boundary layer features on PBL depths at coastal locations.…”

Optimization of Terrestrial Ecosystem Model Parameters Using Atmospheric CO2 Concentration Data With the Global Carbon Assimilation System (GCAS)

“…In addition, errors caused by simulations of the boundary layer height in the transport model also must be considered in the future. The height of the boundary layer is a critical parameter in atmospheric transport models, since it controls the extent of the vertical mixing of trace gases emitted near the surface (Koffi et al, ).…”