Understanding the relative importance of different precipitation generating weather systems and quantifying their efficiencies

 

Understanding rainfall and its extremes is essential for quantifying weather and climate related risks, and the management of water resources. However, climate projections of rainfall have large uncertainties because of differing sensitivities to changes in dynamic, thermodynamic and microphysical factors. Emergent statistical constraints derived from observations and high resolution simulations can be used to reduce these uncertainties, but must be based on process understanding to be robust.

Our recent work shows that clustering rainfall data into regions of similar wet day frequency, regardless of geographical separation, uncovers a strong correlation between wet day occurrence and daily rainfall accumulation distributions. This relationship is robust across a range of observational datasets with differing spatial resolutions.

We hypothesise that this relationship shows that the presence or absence of precipitation generating weather systems (atmospheric rivers, cyclones, fronts and mesoscale convective storms) rather than their individual intensities is critical for daily rainfall totals. In this presentation, we will first examine whether the probability of specific dynamic, thermodynamic and microphysical states drives wet day occurrence. We will also use feature analysis and tracking schemes to identify how the distribution of each of these dynamic, thermodynamic and microphysical states varies for each precipitation generating weather system. This potentially allows a quantification of the importance of different precipitation generating systems for different wet day occurrences and how each contributes to daily accumulation distributions. This expands on previous work which has shown that atmospheric rivers, cyclones, fronts and mesoscale convective storms have varying relationships to rainfall and their extremes. In particular, it allows us to identify their relative importance and explains their relative efficacy for precipitation generation.