Figure - available from: Journal of Advances in Modeling Earth Systems
This content is subject to copyright. Terms and conditions apply.
Source publication
A simple parameter nudging procedure is described that systematically reduces near‐analysis time errors in the surface net shortwave flux in the Navy ESPC (Earth System Prediction Capability) system, a global coupled forecast system that is the product of a continuing development effort at the U. S. Naval Research Laboratory. The procedure generate...
Similar publications
Atmospheric ionization produced by cosmic rays has been suspected to influence aerosols and clouds, but its actual importance has been questioned. If changes in atmospheric ionization have a substantial impact on clouds, one would expect to observe significant responses in Earth’s energy budget. Here it is shown that the average of the five stronge...
Citations
This paper describes the convection parameterization in the Navy Earth System Prediction Capability (ESPC) system developed at the Naval Research Laboratory, with a focus on the scheme configuration in the v2.0 system. The parameterization is an update of a modification of the Kain–Fritsch convection scheme by Ridout et al. based on an assumed quasi-balance of updraft parcel buoyancy at the cloud-base level. Scheme updates include the treatment of updraft/environment mixing and additional updraft model features, including a parameterized reduction in net detrainment in cases of significant near-cloud upward motion, and a modified cloud-top condition. The scheme includes two convection modes: a turbulence-triggered and a dynamically triggered mode. Hindcast sensitivity with Navy ESPC to features of the scheme is investigated with 45-day integrations from 1 November 2011 for a portion of the Dynamics of the Madden–Julian Oscillation (DYNAMO) research program observational period that overlaps with the occurrence of two episodes of the MJO. The modified updraft mixing is critical in the hindcasts for consistent MJO eastward propagation, whereas the additional updraft updates significantly improve the representation of small-scale rainfall variability, while helping to inhibit development of excessive low-level easterly flow. The added turbulence-triggered convection mode helps to improve the representation of the separation of periods of enhanced MJO convection. The relative occurrence frequency of convective cloud-top height and column water vapor in the equatorial Indo-Pacific is investigated in the hindcasts, showing significant similarities with satellite retrieval results.
Significance Statement
This study describes the scheme used to represent the effects of convective clouds such as cumulus and cumulonimbus (thunderstorm clouds) in computerized 45-day global forecasts of the Earth system in a forecast model developed at the Naval Research Laboratory, focusing on the version currently undergoing testing for use by the U.S. Navy. Some of the development history and physical basis for the scheme are presented, and results from test simulations are included. The test results investigate potential forecast sensitivity to various features of the scheme and illustrate that the scheme can successfully represent certain effects of convective clouds on large-scale storm systems in the tropics that have global-scale impacts on extended-range (several weeks) prediction of the Earth’s atmosphere/ocean system.
The West African westerly jet (WAWJ) is a key rainfall producing system over West Africa. While past studies have examined the dynamics of the WAWJ and its influences on Sahelian rainfall, there is no information on how well the jet is simulated by contemporary climate models. This thesis examines the capability of the Coupled Model Intercomparison Project version 6 models (CMIP6) and the Atmospheric component of Model Prediction Across Scale (MPAS) in simulating the WAWJ, its moisture transport over West Africa, and its influence on Sahelian precipitation. Three types of climate dataset (observation, reanalysis, and simulations) were analysed in the thesis. The observation dataset (from the Climate Research Unit or ‘CRU') and the reanalysis dataset (from the European Centre for Medium-Range Weather Forecast Atmospheric Reanalysis, or ‘ERA5') were used to evaluate 26 CMIP6 models (for 35 years: 1980–2014) and MPAS (for 30 years: 1985–2014). To investigate the sensitivity of the simulated WAWJ to model resolution, two additional simulations were performed with MPAS, focusing on WAWJ strong years (1989, 1994, and 1999) and weak years (1986, 1990, and 2000). This thesis defined the WAWJ as a low-level westerly jet (with average maximum speed of 5 m s-1 ) at 925 hPa over the eastern Atlantic Ocean and over the West African coast and used standard statistical metrics to quantify the capability of the models in simulating the characteristics and influences of the WAWJ. The majority of the CMIP6 models capture the temporal and spatial structures of the WAWJ and agree with ERA5 that the jet attains its maximum speed in August. However, most simulated jets form earlier and are stronger than the observed jet. While most of the CMIP6 models capture the link between the jet and temperature distribution over West Africa, they struggle to reproduce the relationship between the jet and precipitation distribution over the sub-continent, especially over the Sahel. Most models failed to replicate the increase in the moisture transport (i.e., the eastward and north-eastward transports) associated with a stronger WAWJ, as in ERA5. Some models capture the increased moisture transport but do not translate it to increased precipitation over the Sahel. MPAS performs well in simulating various features in temperature, precipitation, and wind fields over West Africa, but with wet and warm biases over the region. It also simulates the WAWJ but the simulated jet forms too early and is too strong. In addition, the position and dynamics of the simulated jet differ from the observed jet because the model fails to capture the local pressure gradient force that induces the WAWJ over the Atlantic Ocean. The model underestimates the relationship between the WAWJ and Sahelian precipitation because it limits WAWJ moisture transports to the southern part of Sahel, in contrast to the observation. The sensitivity simulations show that increasing the horizontal resolution of the model does not improve the MPAS simulation of the WAWJ or the WAWJ moisture transport to the Sahel. The results of the study have application in improving the climate models for seasonal predictions and future projections over West Africa, especially over the Sahel.
