Multifractal analysis of Liquid Water Content vertical and temporal variability

Driven by complex mechanisms, precipitation exhibits extreme variability across scales both in space and time. A clearer insight into this variability can be obtained by exploring multiple parameters, such as the Liquid Water Content (LWC). It is a measurement that quantifies the amount of liquid water available in the atmosphere and as such it provides valuable information about precipitation variability across space and time. While extensive research has focused on analyzing LWC variability at the surface level, studies addressing the vertical variability remain relatively limited. However, it contributes to better understanding of rainfall dynamics, and notably the variability occurring at scales smaller than radar gate.

Within this scope, six months of a Micro Rain Radar PRO (MRR-PRO) observations were gathered in Ecole nationale des ponts et chaussées, Institut Polytechnique de Paris, which is located next to Paris, France. The MRR-PRO is a K-band weather radar that measures hydrometeors fall velocity up to more than 4 kilometers of altitude above its position with a 35 meters spatial resolution and a 10 seconds time step. From collected data and simple assumptions, various quantities related to rainfall drop size distribution including LWC can be derived. The generated data were analyzed to study the spatial and temporal variations of LWC using Universal Multifractals (UM); which is a physically based framework that assesses the variability of geophysical fields across wide ranges of scales with the help of only three parameters with physical interpretation.

In this study, two types of UM analysis are implemented. As a first step, the time series of  LWC at  each altitude is studied. As a second step, vertical profiles of LWC are analyzed and UM parameters characterizing vertical variability are derived. Obtained results and their interpretation in a space-time framework will be presented and discussed.

Authors acknowledge the France-Taiwan Ra2DW project for financial support (grant number by the French National Research Agency – ANR-23-CE01-0019-01).