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Abstract:
Common transport models use the mixing height (MH) to determine turbulent
coefficients and to obtain tracer concentrations in the planetary boundary layer
(PBL). We conducted a pseudo data experiment to elucidate the impact of assimilating
MHs to improve CO2 transport within the Stochastic Time-Inverted Lagrangian
Transport model (STILT). Transport of CO2 was simulated for August
2006 with a receptor located at Bialystok, Poland. STILT was driven by meteorology
obtained from the Weather Research and Forecasting (WRF) model, using the
Yonsei University (YSU) and Mellor-Yamada-Janjić (MYJ) PBL parameterizations,
which differ substantially in the produced MHs. To quantify model-data
mismatch in CO2 to errors in vertical mixing, we defined the WRF-YSU simulation
as known truth. Pseudo MH observations were sampled from WRF-YSU at locations
of real radiosonde stations. These point observations were interpolated in
space-time to the entire WRF domain using kriging with an external drift, which
combines observed and modeled MHs to create a “best guess” MH field. We
prescribed MHs in STILT driven by WRF-MYJ winds with the best guess to study
the impact on CO2 concentrations. Differences in CO2 between the STILT simulations
were on the order of ~0–1 and ~1–10 ppm on average (i.e., bias), with
standard deviations of ~1–3 and ~4–14 ppm (random error) during day (12 UTC)
and nighttime (0 UTC), respectively. These were reduced when using STILT with
the best guess (~50%–80% of the bias, ~10%–20% of the random error). Simulated
CO2 concentrations and MHs were also compared to measurements made at the
Bialystok tall tower.
