Impact of Assimilating Outflow Layer Dropsonde Observations Collected during the TCI Field Campaign on the Prediction of Intensity and Structure of Hurricane Patricia (2015)

The dropsondes released during the Tropical Cyclone Intensity (TCI) field campaign provided kinetic and thermodynamic measurements of tropical cyclones (TC) at both the outflow layer and the inner core region with high resolution. Such observations provided unprecedented opportunity to advance the understanding of the role of the outflow layer on hurricane intensity and structure evolution. This study investigates the impact of the TCI dropsonde observations in the outflow layer on the analyses and prediction of hurricane Patricia (2015) during its rapid intensification (RI) phase using an ensemble-variational hybrid data assimilation system. In the baseline experiment, both the kinetic and thermodynamic observations of TCI dropsondes at all levels are assimilated. The wind and thermodynamic observations in the outflow layer are respectively denied to investigate their impacts.

By verifying the analyses against the independent Atmospheric Motion Vector (AMV) observations, it was found that the assimilation of the TCI upper-level wind correctly strengthens both the tangential and radial wind in the near-core region. Additionally, the analyses produced by assimilating the thermodynamic observations in the outflow layer produce a warmer and dryer core at high levels.

Assimilating the kinetic and thermodynamic observations in the outflow layer both improve the predictions of RI. By comparing the baseline and data-denial experiments, the assimilation of the outflow layer wind induces a stronger secondary circulation. The stronger radial inflow wind provokes stronger updraft in the eyewall, resulting in more latent heating release. This process leads to stronger warming in the eye especially at low and mid troposphere. In addition, the warmer high-level inner core in analyses due to the ingestion of the TCI thermodynamic observations produces a stronger subsidence adiabatic warming of the upper-level warm core and thus contributes to the improved intensity forecasts.

In view of the high resolution of TCI dropsonde observations, efforts are ongoing to study the impact of both the vertical and horizontal density of the TCI dropsonde data using an enhanced model resolution Results will be discussed in the conference.