How Well Tall Tower Measurements Characterize the Mid-Planetary Boundary Layer (PBL) CO2 Mole Fraction
L. Haszpra1, Z. Barcza2, T. Haszpra3, Z. Patkai4 and K.J. Davis5
1Hungarian Meteorological Service, Geodetic & Geophysical Institute, Research Centre for Astronomy & Earth Sciences, Hungarian Academy of Science, Budapest, Hungary; +361-346-4816, E-mail: firstname.lastname@example.org
2Eötvös Loránd University, Department of Meteorology, Budapest, Hungary
3Eötvös Loránd University, Institute of Theoretical Physics, Budapest, Hungary
4Hungarian Meteorological Service, Budapest, Hungary
5Pennsylvania State University, Department of Meteorology, University Park, PA 16802
Characteristic PBL CO2 mole fraction data are needed by 3-dimensional transport models, carbon budget models as input and validation, as well as calibrations for space-borne observations. Tall tower CO2 mole fraction measurements (10 - 115 m above ground) at a rural site in Hungary and regular airborne vertical mole fraction profile measurements (136 vertical profiles) above the tower, allowed us to estimate how well a tower of a given height could estimate the mid-PBL CO2 mole fraction. Taking into account the significantly different dynamics of the lower troposphere in the different seasons, the statistical evaluation of the bias between the real mid-PBL CO2 mole fraction (measured by the aircraft), and the measurement at a given elevation above the ground was performed separately for the summer and winter half years. Under the low elevation, mid-continental conditions at the site of the experiment, a tower of <100 m overestimates the mid-PBL CO2 mole fraction by 1.1 - 1.3 μmol mol -1 (median) in winter and underestimate it by 2.1 μmol mol -1 at 10 m above the ground in summer. The median bias falls below 0.2 μmol mol-1 above 220 m and 350 m, respectively. It was also studied whether additional vertical flux measurements and the application of the Virtual Tall Tower (VTT) concept could improve the mid-PBL CO2 mole fraction estimations. In summer, in the case of a tower of 10 m height, the VTT method could improve the estimation by 0.8 μmol mol -1 (median). In the case of a tower taller than 100 m and in winter, when the vertical mixing of the atmosphere is limited, the improvement is insignificant.