Temperature and water vapour measurements in the framework of the Network for the Detection of Atmospheric Composition Change (NDACC)
Authors: De Rosa Benedetto , Di Girolamo Paolo , Summa Donato 
Published: February 2020

Abstract. The BASIL Raman lidar system entered the
International Network for the Detection of Atmospheric Composition Change
(NDACC) in 2012. Since then, measurements have been carried out routinely on a
weekly basis. This paper reports specific measurement results from this
effort, with a dedicated focus on temperature and water vapour profile
measurements. The main objective of this research effort is to provide a
characterisation of the system performance. The results illustrated in this
publication demonstrate the ability of BASIL to perform measurements of the
temperature profile up to 50 km and of the water vapour mixing ratio profile
up to 15 km, when considering an integration time of 2 h and a vertical
resolution of 150–600 m; the mean measurement accuracy, determined based on
comparisons with simultaneous and co-located radiosondes, is 0.1 K (for the temperature profile) and 0.1 g kg−1 (for the water vapour mixing ratio profile) up to the upper troposphere. The relative humidity
profiling capability up to the tropopause is also demonstrated by combining
simultaneous temperature and water vapour profile measurements. Raman lidar measurements are compared with measurements from additional
instruments, such as radiosondes and satellite sensors (IASI and AIRS),
as well as with model reanalyses data (ECMWF and ECMWF-ERA). We focused our
attention on six case studies collected during the first 2 years of system operation (November 2013–October 2015). Comparisons between
BASIL and the different sensor/model data in terms of the water vapour mixing
ratio indicate biases in the altitudinal interval between 2 and 15 km that are always within ±1 g kg−1 (or ±50 %), with minimum values
being observed in the comparison between BASIL and radiosonde measurements (±20 %
up to 15 km). Results also indicate a vertically averaged mean mutual bias
of −0.026 g kg−1 (or −3.8 %), 0.263 g kg−1 (or 30.0 %), 0.361 g kg−1 (or 23.5 %), −0.297 g kg−1 (or −25 %) and −0.296 g kg−1 (or −29.6 %) when comparing BASIL with radiosondes, IASI,
AIRS, ECMWF and ECMWF-ERA respectively. The vertically averaged mean absolute
mutual biases are somewhat higher, i.e. 0.05 g kg−1(or 16.7 %), 0.39 g kg−1 (or 23.0 %), 0.57 g kg−1 (or 23.5 %), 0.32 g kg−1
(or 29.6 %) and 0.52 g kg−1 (or 53.3 %), when comparing BASIL with
radiosondes, IASI, AIRS, ECMWF and ECMWF-ERA respectively. The comparisons in terms of temperature measurements indicate
mutual biases in the altitudinal interval between 3 and 30 km that are always within
±3 K, with minimum values being observed in the comparison between BASIL
and radiosonde measurements (±2 K within this same altitudinal interval). Results
also reveal mutual biases within ±3 K up to 50 km for most
sensor/model pairs. Furthermore, a vertically averaged mean mutual
bias of
−0.03, 0.21, 1.95, 0.14 and 0.43 K is found between BASIL and the radiosondes, IASI, AIRS, ECMWF and ECMWF-ERA respectively. The vertically averaged absolute
mean mutual biases between BASIL and the radiosondes, IASI, AIRS, ECMWF and
ECMWF-ERA are 1.28, 1.30, 3.50, 1.76 and 1.63 K respectively. Based on the
available dataset and benefiting from the fact that the BASIL Raman lidar could be compared with all other sensor/model data, it was possible to
estimate the overall bias of all sensors/datasets: −0.04 g kg−1 ∕ 0.19 K, 0.20 g kg−1 ∕ 0.22 K, −0.31 g kg−1 ∕ −0.02 K, −0.40 g kg−1 ∕ −1.76 K, 0.25 g kg−1 ∕ 0.04 K and 0.25 g kg−1 ∕ −0.24 K
for the water vapour mixing ratio/temperature profile measurements carried
out by BASIL, the radiosondes, IASI, AIRS, ECMWF and ECMWF-ERA respectively.