Collaborative Research: Measurement and Analysis of the Preconvective Boundary Layer and Convection Initiation during International H2O Project (IHOP)

This collaborative project between the University of Oklahoma and the Pennsylvania State University is part of the International H2O Project (IHOP). The IHOP is a large multi-agency, multi-investigator project that focuses on the measurement of water vapor and water vapor variability. The goal of this project is to improve understanding of convective initiation, increase short-term precipitation forecast skills and test the capabilities of various instruments to measure the four dimensional characteristics of water vapor. The field phase of the IHOP will be conducted during the Spring and Summer of 2002 and will provide a wide range of mesoscale meteorological observations for studies to gain a better understanding of the scales of, and processes influencing, water vapor variability.

The goal of this hypothesis-driven research is to improve understanding of the processes leading to the initiation of deep, moist cumulus convection. Though several studies have examined certain aspects of boundary layer structure little is known about what causes convective initiation. IHOP will provide the comprehensive data sets needed to begin evaluating and revising hypotheses concerning convection initiation processes and the role of boundary layer water vapor. The Principal Investigators will acquire and analyze three dimensional radar-derived boundary layer airflow and in-situ measurements of winds and thermodynamic parameters from mobile facilities. The combination of boundary layer airflow with in-situ measurements of absolute humidity and virtual temperature provides the only means of documenting the dynamical and transport processes acting in the boundary layer to regulate precipitable water and force the development of secondary circulations. Thus these observations are essential for evaluating hypotheses concerning the impact of water vapor supply and airflow evolution on boundary formation and convection initiation.

Detailed observations will be analyzed in several different ways. Subjective analyses and visualizations will be produced incorporating all available data on relevant scales for convection initiation. Observation density will be enhanced utilizing an advanced time-to-space conversion scheme by distributing nearly conservative variables along Lagrangian trajectories based on multi-Doppler wind syntheses. Finally, these enhanced observations will be assimilated into mesoscale models to determine the dynamical forcing processes controlling the development of localized boundary layer circulations that either promote or prevent convection initiation.

This effort will result in the collection and analysis of an unprecedented data set at scales previously not observed. Through this work, a completely new understanding will emerge regarding the processes occurring near low-level boundaries and how these processes regulate the formation of thunderstorms. The knowledge will be useful for developing new advances, both numerical and subjective, in quantitative precipitation forecasting by improving the ability to forecast if, when, and where convection will develop.