Moisture Structure in the Boundary layer

Comparisons of observations with model analyses showed overestimated specific humidity values in ECMWF's boundary layer (Schäfler et al., 2010, 2011). Most likely these errors are associated to insufficiently parameterized boundary layer processes. The current observational system lacks high-resolution observations of moisture as ground observations are sparse of the oceans and satellite observations have insufficient vertical resolution, especially close to the ground.

As diabatic processes related to the lifting of moist air masses can strongly influence the dynamics of the extratropics an accurate representation of the boundary layer humidity can be crucial. Schäfler and Harnisch (2015) showed that initial condition errors in the low-level moisture supply of a WCB deteriorate the forecast quality. In some unstable flow situations, e.g. baroclinic cyclones, the small-scale errors can grow rapidly and impact the large-scale flow and propagate downstream.

The observation of horizontal moisture transport also provides a link to "atmospheric rivers" (filaments of strong WV transport). These particularly strong exports of tropical moisture can have substantial impact by causing intense rain in the mid-latitudes (e.g. Cordeira et al. 2013)

The collocated deployment of wind and water vapour lidar instruments has shown to be a valuable instrument combination to observe both horizontal (Schäfler et al. 2010) and vertical transport of humidity (Kiemle et al. 2011).

Moisture Structure in the Boundary layer
Research Questions	How does the moisture structure at lower levels evolve? What is the vertical and horizontal structure in the inflow regions? Sharp transition from smooth boundary layer to synoptically forced region?
Planned Observations	HALO and Falcon (dropsondes, DIAL, wind lidar, radar)
Obsevation strategy	several transects in pre-saturated environment where lifting starts, e.g. the inflow region of WCBs before the ascent starts and clouds develop HALO water vapour with lidar and dropsondes (T, u, v) for the case that moisture source regions are within the range of the DLR Falcon coordinated flights to measure moisture transport (horizontal and vertical) are possible atmospheric river situation would be of high interest radar obs to observe changing cloud structures in different forcing regimes
Schematic flight plan:

• Cordeira JM, Ralph FM, Moore BJ. 2013. The Development and Evolution of Two Atmospheric Rivers in Proximity to Western North Pacific Tropical Cyclones in October 2010. Mon. Wea. Rev., 141, 4234-4255.


• Kiemle C, Brewer WA, Ehret G, Hardesty RM, Fix A, Senff C, Wirth M, Poberaj G, LeMone MA. 2007. Latent heat flux profiles from collocated airborne water vapor and wind lidars during IHOP_2002. J. Atmos. Oceanic Technol. 24: 627-639.


• Schäfler A, Dörnbrack A, Kiemle C, Rahm S, Wirth M. 2010. Tropospheric water vapour transport as determined from airborne lidar measurements. J. Atmos. Oceanic Technol. 27: 2017-2030.


• Schäfler A, Dörnbrack A, Wernli H, Kiemle C, Rahm S. 2011. Airborne lidar observations in the inflow region of a warm conveyor belt. Q. J. R. Meteorol. Soc. 137: 1257-1272.


• Schäfler A, Harnisch F. 2014. Impact of the inflow moisture on the evolution of a Warm Conveyor Belt. Q.J.R. Meteorol. Soc. In press. doi: 10.1002/qj.2360

NAWDEX goals:

• Moisture structure in the boundary layer
• Mixed phase clouds
• Upper level PV
• Diabatic effects on cyclonic systems
• Impacts of tropopause waveguide uncertainty on HIW events
• Moisture and cloud structure in tropopause region
• Quantification of analysis errors
• Lagrangian Tracking of disturbances