Understanding the Characteristics of Precipitation and Their Response to Climate Change

Abstract

In this thesis, I present three projects that target different characteristics of atmospheric precipitation that are not well understood. First, I focus on precipitation extremes in the extratropics and aim to understand changes in vertical velocity which control the spatial variation in the climate-change response of extratropical precipitation extremes. I solve the quasi-geostrophic omega equation and attribute the vertical velocity changes in two ways. In the dry decomposition, a positive contribution by latent heating is largely offset by a negative contribution from an increase in dry static stability. In the moist decomposition, changes in moist static stability play a key role. Second, I look at the power-law frequency distributions and fractal dimensions of tropical precipitation clusters. I propose a viewpoint that regards precipitation as thresholded islands on a rough column-water vapor (CWV) topography, which is supported by good agreement between the precipitation clusters and CWV islands in frequency distributions and fractal dimensions. I further show that self-affine surfaces with a roughness exponent of 0.3 reproduce these statistics, and that the self-affine scaling theory provides analytical relations between multiple power-law exponents. Third, I further investigate the general dynamics behind tropical precipitation and present a 2-dimensional conceptual model to study tropical convective organization. The model uses the column moist static energy (CMSE) as a prognostic variable and has terms parameterized by diagnosing a high-resolution simulation with explicit convection. Through analyzing the conceptual model, I show that self-aggregation is due to the interplay between the amplifying effect of vertical advection and the smoothing effect of horizontal advection, with relatively weaker contributions from the radiative forcing and surface fluxes. Furthermore, I find that a temporal red noise and a diffusive horizontal advection term sets the CMSE spectrum shape which approximately matches that in the high-resolution simulation except for a shallowing of slope at high wavenumber. Overall, these contributions combine to make progress in understanding the dynamics of precipitation in the current climate and under climate change.