arXiv subjects

Douglas J. Parker

Publications and source records attributed to Douglas J. Parker.

4 recordsLinked to original sources

arXiv2026

Can we create a `race to the top' for weather forecasts to inform smallholder farmer decisions?

Artificial-intelligence weather prediction (AIWP) models have made it possible to produce high-quality tailored forecasts with limited computational resources. This advance has the potential to benefit hundreds of millions of farmers in low- and middle-income countries who lack access to forecasts of critical weather phenomena. However, it can be difficult for key stakeholders to evaluate forecast quality, risking a "race to the bottom" as cheap but low-quality forecasts crowd out forecasts that would benefit farmers. We propose a set of principles and protocols for evaluating agriculturally-relevant forecasts as a starting point for standards that would let forecasters credibly convey their forecasts' quality.

physics.ao-ph↗

arXiv2025

Radiatively-Cooled Moist Convection under an Idealised Climate Change Scenario: Linear Analysis

In order to explore the effects of climate change on atmospheric convection and the water cycle, we develop and analyse an extension of the Rainy-Bénard model, which is itself a moist version of the Rayleigh-Bénard model of dry convection. Including moisture changes the character of the convection, with condensation providing a source of buoyancy via latent heating. The climate change model is set up by imposing a variable radiative cooling rate, prescribing surface temperature and relative humidity, and imposing a moist-pseudoadiabatic profile at the top boundary (a flux boundary condition). The model is analysed across the climate parameter space by examining diagnostics of the model's basic state, and its stability, with Convective Available Potential Energy (CAPE) calculations and a linear stability analysis. We use the linear stability results to identify new parameters relevant for this moist convective system, and to understand how the linear instability responds to the climate parameters. In particular, we define the "Rainy number" as a scaled ratio of positive-area CAPE and diffusion parameters. An alternative radiative-based Rainy number also is shown to describe the parameter space, especially for problems relating to changes in flux conditions. The analysis provides a novel theoretical understanding of how the dynamics and scales of moist convection and hence precipitation will change under climate change.

physics.flu-dyn↗

arXiv2021

Characterising the shape, size and orientation of cloud-feeding coherent boundary layer structures

This paper presents two techniques for characterisation of cloud-feeding coherent boundary layer structures through analysis of large-eddy simulations of shallow cumulus clouds, contrasting conditions with and without ambient shear. The first technique is a generalisation of the two-point correlation function where the correlation length-scale as well as orientation can be extracted. The second technique decomposes the vertical transport by coherent structures by the shape, size and orientation of these structures. It is found that the structures dominating the vertical flux are plume-like in character (extending from the surface into cloud), show small width/thickness asymmetry and rise near-vertically in the absence of ambient wind. The planar stretching and tilting of boundary layer structures caused by the introduction of ambient shear is also quantified, demonstrating the general applicability of the techniques for future study of other boundary layer patterns.

physics.ao-ph↗

arXiv2018

A Simple System for Moist Convection: the Rainy-Benard Model

Raylaigh-Benard convection is one of the most well-studied models in fluid mechanics. Atmospheric convection, one of the most important components of the climate system, is by comparison complicated and poorly understood. A key attribute of atmospheric convection is the buoyancy source provided by the condensation of water vapour, but the presence of radiation, compressibility, liquid water and ice further complicate the system and our understanding of it. In this paper we present an idealized model of moist convection by taking the Boussinesq limit of the ideal gas equations and adding a condensate that obeys a simplified Clausius--Clapeyron relation. The system allows moist convection to be explored at a fundamental level and reduces to the classical Rayleigh-Benard model if the latent heat of condensation is taken to be zero. The model has an exact, Rayleigh-number independent `drizzle' solution in which the diffusion of water vapour from a saturated lower surface is balanced by condensation, with the temperature field (and so the saturation value of the moisture) determined self-consistently by the heat released in the condensation. This state is the moist analogue of the conductive solution in the classical problem. We numerically determine the linear stability properties of this solution as a function of Rayleigh number and a nondimensional latent-heat parameter. We also present a number of turbulent solutions.

physics.ao-ph↗