Assimilation of DAWN Doppler wind lidar data during the 2017 Convective Processes Experiment (CPEX): impact on precipitation and flow structure
Abstract. An improved representation of 3-D air motion and
precipitation structure through forecast models and assimilation of
observations is vital for improvements in weather forecasting capabilities.
However, there are few independent data to properly validate a model
forecast of precipitation structure when the underlying dynamics are
evolving on short convective timescales. Using data from the JPL
Ku/Ka-band Airborne Precipitation Radar (APR-2) and the 2  µ m Doppler Aerosol
Wind (DAWN) lidar collected during the 2017 Convective Processes Experiment
(CPEX), the NASA Unified Weather Research and Forecasting (WRF) Ensemble
Data Assimilation System (EDAS) modeling system was used to quantify the
impact of high-resolution sparsely sampled DAWN measurements on the
analyzed variables and on the forecast when the DAWN winds were assimilated.
Overall, the assimilation of the DAWN wind profiles had a discernible impact
on the wind field as well as the evolution and timing of the 3-D precipitation
structure. Analysis of individual variables revealed that the assimilation
of the DAWN winds resulted in important and coherent modifications of the
environment. It led to an increase in the near-surface convergence, temperature,
and water vapor, creating more favorable conditions for the development of
convection exactly where it was observed (but not present in the control
run). Comparison to APR-2 and observations by the Global Precipitation
Measurement (GPM) satellite shows a much-improved forecast after the
assimilation of the DAWN winds – development of precipitation where there
was none, more organized precipitation where there was some, and a much more
intense and organized cold pool, similar to the analysis of the dropsonde
data. The onset of the vertical evolution of the precipitation showed similar
radar-derived cloud-top heights, but delayed in time. While this
investigation was limited to a single CPEX flight date, the investigation
design is appropriate for further investigation of the impact of airborne
Doppler wind lidar observations upon short-term convective precipitation
forecasts.