How Can Existing Ground-Based Profiling Instruments Improve European Weather Forecasts?

Abstract

To realize the promise of improved predictions of hazardous weather such as flash floods, wind storms, fog, and poor air quality from high-resolution mesoscale models, the forecast models must be initialized with an accurate representation of the current state of the atmosphere, but the lowest few kilometers are hardly accessible by satellite, especially in dynamically active conditions. We report on recent European developments in the exploitation of existing ground-based profiling instruments so that they are networked and able to send data in real time to forecast centers. The three classes of instruments are i) automatic lidars and ceilometers providing backscatter profiles of clouds, aerosols, dust, fog, and volcanic ash, the last two being especially important for air traffic control; ii) Doppler wind lidars deriving profiles of wind, turbulence, wind shear, wind gusts, and low-level jets; and iii) microwave radiometers estimating profiles of temperature and humidity in nearly all weather conditions. The project includes collaboration from 22 European countries and 15 European national weather services, which involves the implementation of common operating procedures, instrument calibrations, data formats, and retrieval algorithms. Currently, data from 265 ceilometers in 19 countries are being distributed in near–real time to national weather forecast centers; this should soon rise to many hundreds. One wind lidar is currently delivering real time data rising to 5 by the end of 2019, and the plan is to incorporate radiometers in 2020. Initial data assimilation tests indicate a positive impact of the new data.

Contrasting Air Mass Advection Explains Significant Differences in Boundary Layer Depth Seasonal Cycles Under Onshore Versus Offshore Flows

“…Numerous research efforts were made to investigate the spatial (local to regional scale) and temporal (diurnal and seasonal time scales) BLD variability over land surface (e.g., Illingworth et al, 2018) and spatiotemporal variability of the depths of the marine boundary layer (MBL) over different oceans and seas (S. Liu & Liang, 2010). However, empirical studies for coastal regions are often limited in scope, as they were largely confined to short-term case studies or over a single coastal region (e.g., Angevine et al, 2006;Stauffer et al, 2015).…”

A robust automated technique for operational calibration of ceilometers using the integrated backscatter from totally attenuating liquid clouds

“…The key technical properties of the ceilometers used by the Met Office are summarised in Table 1. In brief, the Vaisala CL31 ceilometers use an InGaAs diode laser which emits pulses with an energy of 1.2 µJ at a pulse repetition frequency (prf) of 10 kHz with a central wavelength of 910 ± 10 nm, though the typical spectral width is more often 4 nm (Kotthaus et al, 2016;Markowicz et al, 2008). At these wavelengths, attenuation by water vapour is significant, a fact overlooked by O'Connor et al (2004).…”

“…If ceilometer data are to be used in an operational context, and potentially for data assimilation, accurate calibration is essential when verifying model performance by forward modelling the attenuated backscatter; for example, Illingworth et al (2019) show that a calibration accuracy of 10 % is needed when deriving O-B statistics obtained by comparing the observed ceilometer backscatter (O) from Saharan dust with the forward modelled backscatter (B) from the ECMWF CAMS model. The World Meteorological Organisation requirements (OSCAR, 2018) suggest the goal for ice water content (IWC) observations is to have an accuracy of 10 % and for aerosol optical extinction to have an absolute accuracy of 0.01 km −1 , but no fractional accuracy is quoted.…”

Meteorological conditions affecting renewable energy

“…Ceilometers can also be used to detect the aerosol layers (and to obtain mixing layer height; Wiegner et al, 2014) and precipitation. Traditionally ceilometers are used at airports to detect the cloud base height and sky condition information, and therefore there is a dense network of ceilometers distributed around the world (Illingworth et al, 2019). This is a notable benefit compared to other cloud profiling instruments (such as cloud radars, research lidars) which are not as densely distributed.…”

“…Ceilometers are often operated in large networks (e.g. by national weather services; Illingworth et al, 2015), which are now being incorporated within harmonized pan-continental networks such as E-PROFILE (Illingworth et al, 2019), through which the profile is being recorded. Thus, implementing ceilometer methods for evaluating cloud and radiation model forecasts would be a beneficial addition to the more comprehensive but sparse cloud profiling.…”