Meteorological applications of a continuously-operating micropulse lidar in Barcelona, Spain

Planetary boundary-layer (PBL) height is a critical variable in meteorological and air quality modeling applications, as it typically indicates the physical top of atmospheric mixing from the surface. In this study we show the potential of a continuously-operating micropulse lidar (MPL) for the purpose of regional mesoscale model validation and physics package testing. Complementary objectives include evaluation of the PBL height diurnal cycle from the MPL and an analysis of seasonal PBL heights estimated from the MPL and radiosoundings. We compare two methods of retrieving daytime PBL heights from radiosoundings; the parcel method and the bulk Richardson number approach.

The area of interest is Barcelona, located in the northeast Iberian Peninsula. The region is characterized by complex mesoscale interactions between the Western Mediterranean basin and the nearby orography. The time period of interest is spring 2015 (M-A-M) when the MPL recorded continuous optical backscatter at 30-s temporal and 15-m vertical resolution. The MPL at Barcelona is a newly-inducted station in the NASA Micropulse Lidar Network (MPLNET). Daily 12 UTC radiosonde measurements are obtained from the Meteorological Service of Catalonia. Over the entire spring season the mean PBL height was 0.91 ± 0.34 km, with a minimum of 0.37 km and a maximum of 2.0 km. The spring 2015 average is very close to the long-term (2003-2014) mean PBL height of 0.92 km, with a relatively flat linear trend from March to April and a strong (0.17 km) decline from April to May. This fits close to the long-term bimodal distribution of PBL height over Barcelona, with peaks in both March and August.

It is well known that PBL height is controlled by both synoptic and mesoscale processes so we objectively categorize the spring 2015 season by general synoptic flow at three arriving altitudes. Over one-third of spring 2015 days were controlled by regional recirculations arriving at 1.5 km altitude, determined using information from a cluster analysis of back-trajectories covering a 16-yr period, in addition to satellite images, lidar observations, and nearby radiosoundings. Other frequent synoptic flows were from the west, north, and north-west at all three arriving altitudes. The objectively-determined synoptic flow types are used to evaluate simulations from the numerical weather prediction model and perform comparisons with PBL heights from the MPL.

The Weather Research and Forecasting (WRF) model version 3.5 is run for select cases from each of the most frequent synoptic flows over the Catalonia domain. The WRF model is configured with two one-way nested domains, with an inner domain of 4 km grid-spacing. Physics parametrizations selected include the non-local Assymetric Convective Model Version 2 (ACM2) PBL scheme as it has been shown to perform well in complex areas. WRF model results are used to investigate the differences in PBL height throughout the season observed by the MPL and radiosoundings. Also, daytime WRF model-simulated PBL heights are validated against estimates retrieved using the MPL.