Diurnal and Seasonal Trends in Convective Mixed-Layer Heights Estimated from Two Years of Continuous Ceilometer Observations in Vancouver, BC

Abstract

Twenty-six months of continuous ceilometer data are used to estimate the convective mixed-layer height for 710 days by identifying backscatter gradients associated with the entrainment zone. To accomplish this, a semi-automatic procedure is developed that removes all non-applicable data before applying a mixed-layer height algorithm to the backscatter profiles. Two different algorithms for estimating the mixed-layer height are assessed: the minimum-gradient method and the ideal-profile method. The latter of these two algorithms is found to be more robust. Comparisons of mixed-layer height values estimated from the ceilometer agree with previous observations with slightly higher estimates in the mornings and evenings. For clear days with no cumulus cloud formation, the seasonal cycle in mixed-layer heights peaks in late June to early July. Daily maximum values are suppressed by the site's coastal location, remaining below 800 m for all but a few days. The mean daily maximum mixed-layer height increases by 384 m for days with boundary-layer clouds. The mean summer diurnal trend is found not to differ greatly from that in spring on clear days, while days with boundary-layer clouds have higher spring values than in summer. Net surface heat flux and synoptic stability likely have the largest influence on the mixed-layer heights. Additionally, large intra-monthly variability suggests a strong influence from regional dynamics.

Variability of Urban Aerosols over Santiago, Chile: Comparison of Surface PM10 Concentrations and Remote Sensing with Ceilometer and Lidar

“…Its setup in Santiago provides mean profiles of rangecorrected attenuated backscatter (in units of 1/(10 5 ·srad·km), hereafter referred to as backscatter units, bu) every 4 to 8 s with vertical resolution of 20 m. We discard in the analysis the first two data levels because they show apparently unphysical high values. Similar measure was taken by Sundström et al (2009) and van der Kamp and McKendry (2010a), the latter mentioning that more recent versions of the CL31 firmware have corrected this problem. In the vertical, the analysis is limited up to 1000 m above the ground, and in time the profiles are averaged over 30-minute periods.…”

“…One particular class of lidar deserves special mention. Although initially conceived as instruments for automatic cloud base measurements, lidar ceilometers have been shown to describe ABL aerosol layers during cloud-free conditions quite well (Eresmaa et al, 2006;Münkel et al, 2007;Sundström et al, 2009;Van der Kamp and McKendry, 2010a).…”

Comparison of aerosol lidar retrieval methods for boundary layer height detection using ceilometer aerosol backscatter data

“…For text-shortening reasons and because at the CL31 wavelength the aerosol backscatter coefficient dominates over the molecular backscatter coefficient inside the BL and clouds, these profiles are called aerosol backscatter profiles in this paper. Aerosol backscatter profiles with signals from clouds, rain, or fog are identified as signals higher than 2000 × 10 −9 m −1 sr −1 and were not used for this BLH comparison (Kamp and McKendry, 2010).…”

Continuous 1064/532 nm Lidar Measurements (CORALNet-UBC) in Vancouver, British Columbia: Selected Results from a Year of Operation

“…Algorithms developed for the detection of the MLH height for the CL31 ceilometer 8 km to the southeast (Fig. 1) are described by van der Kamp and McKendry (2010) and are currently being adapted for routine application to the CORALNet-UBC data.…”

“…The colour palette represents aerosol backscatter, with warm colours indicating high aerosol concentration and cold colours indicating weak backscatter from aerosols. The grey line shows the MLH diagnosed from the CL31 ceilometer using standard algorithms (van der Kamp and McKendry, 2010) and the black line the lidarbased MLH. Wind vectors are shown in the bottom panel and indicate offshore winds for the entire period with a switch from southerly flows to easterly winds at around midday.…”