TY - JOUR
T1 - The Impact of the Afternoon Planetary Boundary-Layer Height on the Diurnal Cycle of CO and CO 2 Mixing Ratios at a Low-Altitude Mountaintop
AU - Lee, Temple R.
AU - De Wekker, Stephan F.J.
AU - Pal, Sandip
N1 - Funding Information:
Acknowledgements This research and maintenance of the Pinnacles site was partly funded by an MOU between the NOAA Earth System Research Laboratory (ESRL) Global Monitoring Division, by NOAA award NA13OAR4310065, and by NSF-CAREER award ATM-1151445. We thank Željko Vecˇenaj at the University of Zagreb for advice on instrument maintenance. We acknowledge Arlyn Andrews at NOAA ESRL as the primary provider of the CO mixing-ratio data, and Jonathan Kofler and Jonathan Williams at NOAA ESRL who assisted with the installation and maintenance of the CO and CO2 mixing-ratio monitoring system. We
PY - 2018/7/1
Y1 - 2018/7/1
N2 - Mountaintop trace-gas mixing ratios are often assumed to represent free atmospheric values, but are affected by valley planetary boundary-layer (PBL) air at certain times. We hypothesize that the afternoon valley–PBL height relative to the ridgetop is important in the diurnal cycle of mountaintop trace-gas mixing ratios. To investigate this, we use, (1) 4-years (1 January 2009–31 December 2012) of CO and CO 2 mixing-ratio measurements and supporting meteorological observations from Pinnacles (38. 61 ∘N , 78. 35 ∘W , 1017 m a.s.l.), which is a monitoring site in the Appalachian Mountains, (2) regional O 3 mixing-ratio measurements, and (3) PBL heights determined from a nearby sounding station. Results reveal that the amplitudes of the diurnal cycles of CO and CO 2 mixing ratios vary as a function of the daytime maximum valley–PBL height relative to the ridgetop. The mean diurnal cycle for the subset of days when the afternoon valley–PBL height is at least 400 m below the ridgetop shows a daytime CO mixing-ratio increase, implying the transport of PBL air from the valley to the mountaintop. During the daytime, on days when the PBL heights exceed the mountaintop, PBL dilution and entrainment cause CO mixing ratios to decrease. This decrease in CO mixing ratio, especially on days when PBL heights are at least 400 m above the ridgetop, suggests that measurements from these days can be used as with afternoon measurements from flat terrain in applications requiring regionally-representative measurements.
AB - Mountaintop trace-gas mixing ratios are often assumed to represent free atmospheric values, but are affected by valley planetary boundary-layer (PBL) air at certain times. We hypothesize that the afternoon valley–PBL height relative to the ridgetop is important in the diurnal cycle of mountaintop trace-gas mixing ratios. To investigate this, we use, (1) 4-years (1 January 2009–31 December 2012) of CO and CO 2 mixing-ratio measurements and supporting meteorological observations from Pinnacles (38. 61 ∘N , 78. 35 ∘W , 1017 m a.s.l.), which is a monitoring site in the Appalachian Mountains, (2) regional O 3 mixing-ratio measurements, and (3) PBL heights determined from a nearby sounding station. Results reveal that the amplitudes of the diurnal cycles of CO and CO 2 mixing ratios vary as a function of the daytime maximum valley–PBL height relative to the ridgetop. The mean diurnal cycle for the subset of days when the afternoon valley–PBL height is at least 400 m below the ridgetop shows a daytime CO mixing-ratio increase, implying the transport of PBL air from the valley to the mountaintop. During the daytime, on days when the PBL heights exceed the mountaintop, PBL dilution and entrainment cause CO mixing ratios to decrease. This decrease in CO mixing ratio, especially on days when PBL heights are at least 400 m above the ridgetop, suggests that measurements from these days can be used as with afternoon measurements from flat terrain in applications requiring regionally-representative measurements.
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U2 - 10.1007/s10546-018-0343-9
DO - 10.1007/s10546-018-0343-9
M3 - Article
AN - SCOPUS:85042619924
SN - 0006-8314
VL - 168
SP - 81
EP - 102
JO - Boundary-Layer Meteorology
JF - Boundary-Layer Meteorology
IS - 1
ER -