Papers by Lawrence Jackson
Simulating the impact of varying vegetation on West African monsoon surface fluxes using a regional convection‐permitting model
Plant-Environment Interactions
On 30 September 2021, the EU CONSTRAIN project hosted an online workshop "The Role of Climat... more On 30 September 2021, the EU CONSTRAIN project hosted an online workshop "The Role of Climate Model Emulators in the IPCC 6th Assessment Report". The workshop appraised recent developments in the use of climate model emulators in the 6th Assessment Report (AR6) of the Intergovernmental Panel on Climate Change (IPCC) which was published on 9 August 2021. The workshop highlighted the many ways in which climate model emulators contributed to AR6. Some of the notable benefits are: Synthesis of multiple lines of evidence and production of 100s of projections central to the assessments of WG1 and WG3. Supporting the IPCC's ambition to produce open science using transparent, accessible models and data. Facilitating communication, collaborative working, and consistency between the working groups and between the chapter teams in WG1. The discussion at the workshop made it clear that emulators offer considerable opportunities to enhance both future climate research and the commu...
This guide provides a practical overview of the first pan-African, kilometre-scale convection-per... more This guide provides a practical overview of the first pan-African, kilometre-scale convection-permitting regional climate simulations (CP4-Africa), run as part of the Future Climate for Africa (FCFA) programme's Improving Model Processes for African Climate (IMPALA) project. CP4-Africa provides the first convection-permitting resolution, multi-year climate simulations for present-day and idealised future climates on an African-wide domain. The simulations have provided an unprecedented level of climate detail across Africa and initial studies have shown improvements in the simulation of many, but not all, aspects of African climate. The goal of this guide is to promote adoption of the CP4-Africa approach within the climate community and is targeted at researchers with interest in progressing this relatively new modelling approach to improve understanding and representation of the drivers of African climate. It is also targeted at potential users of the high-resolution simulation...
Journal of Climate, 2020
The Hadley circulation and tropical rain belt are dominant features of African climate. Moist con... more The Hadley circulation and tropical rain belt are dominant features of African climate. Moist convection provides ascent within the rain belt, but must be parameterized in climate models, limiting predictions. Here, we use a pan-African convection-permitting model (CPM), alongside a parameterized convection model (PCM), to analyze how explicit convection affects the rain belt under climate change. Regarding changes in mean climate, both models project an increase in total column water (TCW), a widespread increase in rainfall, and slowdown of subtropical descent. Regional climate changes are similar for annual mean rainfall but regional changes of ascent typically strengthen less or weaken more in the CPM. Over a land-only meridional transect of the rain belt, the CPM mean rainfall increases less than in the PCM (5% vs 14%) but mean vertical velocity at 500 hPa weakens more (17% vs 10%). These changes mask more fundamental changes in underlying distributions. The decrease in 3-hourly...
Journal of Climate, 2019
The representation of convection remains one of the most important sources of bias in global mode... more The representation of convection remains one of the most important sources of bias in global models, and evaluation methods are needed that show that models provide the correct mean state and variability, both for the correct reasons. Here we develop a novel approach for evaluating rainfall variability due to convectively coupled Kelvin waves (CCKWs) in this region. A phase cycle was defined for the CCKW cycle in OLR and used to composite rainfall anomalies. We characterize the observed (TRMM) rainfall response to CCKWs over tropical Africa in April and evaluate the performance of regional climate model (RCM) simulations: a parameterized convection simulation (P25) and the first pan-Africa convection-permitting simulation (CP4). TRMM mean rainfall is enhanced and suppressed by CCKW activity, and the occurrence of extreme rainfall and dry days is coupled with CCKW activity. Focusing on regional differences, we show for the first time that there is a dipole between West Africa and the...
Journal of Geophysical Research D: Atmospheres, 2013
We used the National Center for Atmospheric Research single column climate model to determine if ... more We used the National Center for Atmospheric Research single column climate model to determine if rapid adjustments to surface heat fluxes contribute to a change in skin surface or surface air diurnal temperature range (DTR) under 2 Â CO 2 and À2% solar forcings. An ensemble of model runs was employed with locations selected to represent a range of different climatic conditions and with forcing implemented hourly throughout the diurnal cycle. The change in skin surface DTR and surface energy fluxes during the 3 days after forcing were used to quantify the rapid adjustment response and temperature related feedback. Averaged over all locations, skin surface DTR reduced by 0.01 C after CO 2 forcing and included a rapid adjustment to skin surface DTR of À0.12 C. Skin surface DTR reduced by 0.17 C after solar forcing and included a rapid adjustment of À0.01 C. The rapid adjustments in skin surface DTR were associated with rapid adjustments in surface sensible and latent heat fluxes necessary to balance the energy budget immediately after forcing. We find that the sensitivity of skin surface DTR to mean temperature related feedback is the same for CO 2 and solar forcings when skin surface DTR rapid adjustments are allowed for. Rapid adjustments played a key role in the geographic variation of the skin surface DTR response to forcing. Our results suggest that diurnal variations in trends of downwelling longwave radiation and rapid reductions in DTR associated with CO 2 forcing potentially contributed to the observed global trend in surface air DTR.
Journal of Geophysical Research-Atmospheres, 2013
We utilize energy budget diagnostics from the Coupled Model Intercomparison Project phase 5 (CMIP... more We utilize energy budget diagnostics from the Coupled Model Intercomparison Project phase 5 (CMIP5) to evaluate the models' climate forcing since preindustrial times employing an established regression technique. The climate forcing evaluated this way, termed the adjusted forcing (AF), includes a rapid adjustment term associated with cloud changes and other tropospheric and land-surface changes. We estimate a 2010 total anthropogenic and natural AF from CMIP5 models of 1.9 AE 0.9 W m À2 (5-95% range). The projected AF of the Representative Concentration Pathway simulations are lower than their expected radiative forcing (RF) in 2095 but agree well with efficacy weighted forcings from integrated assessment models. The smaller AF, compared to RF, is likely due to cloud adjustment. Multimodel time series of temperature change and AF from 1850 to 2100 have large intermodel spreads throughout the period. The intermodel spread of temperature change is principally driven by forcing differences in the present day and climate feedback differences in 2095, although forcing differences are still important for model spread at 2095. We find no significant relationship between the equilibrium climate sensitivity (ECS) of a model and its 2003 AF, in contrast to that found in older models where higher ECS models generally had less forcing. Given the large present-day model spread, there is no indication of any tendency by modelling groups to adjust their aerosol forcing in order to produce observed trends. Instead, some CMIP5 models have a relatively large positive forcing and overestimate the observed temperature change.
Journal of Climate, 2010
The diurnal temperature range (DTR) of surface air over land varies geographically and seasonally... more The diurnal temperature range (DTR) of surface air over land varies geographically and seasonally. The authors have investigated these variations using generalized additive models (GAMs), a nonlinear regression methodology. With DTR as the response variable, meteorological and land surface parameters were treated as explanatory variables. Regression curves related the deviation of DTR from its mean value to values of the meteorological and land surface variables. Cloud cover, soil moisture, distance inland, solar radiation, and elevation were combined as explanatory variables in an ensemble of 84 GAM models that used data grouped into seven vegetation types and 12 months. The ensemble explained 80% of the geographical and seasonal variation in DTR. Vegetation type and cloud cover exhibited the strongest relationships with DTR. Shortwave radiation, distance inland, and elevation were positively correlated with DTR, whereas cloud cover and soil moisture were negatively correlated. A s...
Geophysical Research Letters, 2015
In an assessment of how Arctic sea ice cover could be remediated in a warming world, we simulated... more In an assessment of how Arctic sea ice cover could be remediated in a warming world, we simulated the injection of SO2 into the Arctic stratosphere making annual adjustments to injection rates. We treated one climate model realization as a surrogate “real world” with imperfect “observations” and no rerunning or reference to control simulations. SO2 injection rates were proposed using a novel model predictive control regime which incorporated a second simpler climate model to forecast “optimal” decision pathways. Commencing the simulation in 2018, Arctic sea ice cover was remediated by 2043 and maintained until solar geoengineering was terminated. We found quantifying climate side effects problematic because internal climate variability hampered detection of regional climate changes beyond the Arctic. Nevertheless, through decision maker learning and the accumulation of at least 10 years time series data exploited through an annual review cycle, uncertainties in observations and forc...
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Papers by Lawrence Jackson