ENSO Amplitude Asymmetry in Met Office Hadley Centre Climate Models

Long climate simulations with the Met Office Hadley Centre General Circulation Model show weak El Niño-Southern Oscillation (ENSO) amplitude asymmetry between El Niño and La Niña phases compared with observations. This lack of asymmetry is explored through the framework of a perturbed parameter experiment. Two key hypotheses for the lack of asymmetry are tested. First, the possibility that westerly wind burst activity is biased is explored. It is found that the observed difference in wind burst activity during El Niño and La Niña tends to be underestimated by the model. Secondly, the warming due to subsurface non-linear advection is examined. While the model exhibits non-linear dynamic warming during both La Niña and El Niño, and thus a contribution to ENSO asymmetry, it is shown to be consistently underestimated in comparison with ocean reanalyses. The non-linear zonal advection term contributes most to the deficiency and the simulation of the anomalous zonal currents may be playing a key role in its underestimation. Compared with the ocean reanalyses, the anomalous zonal currents associated with ENSO are too weak in the vicinity of the equatorial undercurrent and the surface wind driven zonal currents extend too deep.

Effects of Whole SST Anomaly in the Tropical Indian Ocean on Summer rainfall Over Central Asia

The effects of sea surface temperature (SST) anomaly in the tropical Indian Ocean (IO) on summer rainfall over central Asia (CA) are investigated using NCEP/NCAR reanalysis circulation data, Hadley Centre SST data, and GPCC gridded precipitation data for 1971–2016. Results show that the SST anomalies over the whole tropical IO play important roles in modulating summer rainfall over southeast CA via the subtropical westerly jet. When the SSTs in the tropical IO are in positive phases, the south Asian monsoon is weakened, which reduces summer rainfall in the Indian monsoon regions corresponding to less release of latent heat. There is an anomalous anticyclone over the Indian Peninsula and an anomalous cyclone in the upper troposphere over CA, corresponding to a shift of the subtropical westerly jet farther south over CA. The southward shift of westerly jet would be responded to anomalous cyclone at 500 hPa over CA and water vapor transported into CA through two steps from the Arabian Sea, above both contribute to more summer rainfall over CA.

The UK-China Climate Science to Service Partnership

We present results from the first 6 years of this major UK government funded project to accelerate and enhance collaborative research and development in climate science, forge a strong strategic partnership between UK and Chinese climate scientists and demonstrate new climate services developed in partnership. The development of novel climate services is described in the context of new modelling and prediction capability, enhanced understanding of climate variability and change, and improved observational datasets. Selected highlights are presented from over three hundred peer reviewed studies generated jointly by UK and Chinese scientists within this project. We illustrate new observational datasets for Asia and enhanced capability through training workshops on the attribution of climate extremes to anthropogenic forcing. Joint studies on the dynamics and predictability of climate have identified new opportunities for skilful predictions of important aspects of Chinese climate such as East Asian Summer Monsoon rainfall. In addition, the development of improved modelling capability has led to profound changes in model computer codes and climate model configurations, with demonstrable increases in performance. We also describe the successes and difficulties in bridging the gap between fundamental climate research and the development of novel real time climate services. Participation of dozens of institutes through sub-projects in this programme, which is governed by the Met Office Hadley Centre, the China Meteorological Administration and the Institute of Atmospheric Physics, is creating an important legacy for future collaboration in climate science and services.

Estimation of Runoff under changed climatic scenario of a Meso Scale River by Neural Network Based Gridded Model Approach

As climate change is linked with changes in precipitation, evapotranspiration and changes in other climatological parameters, these changes will be affected runoff of a river basin. Gomati River basin is the largest river basin among all the river basin of Tripura. Due to the increase in settlement in the Gomati river basin and climate change may threaten natural flow patterns that endure its diversity. This study assesses the impact of climate change on total flow of a catchment in North East India (Gomati River catchment). For this assessment, the Group Method of Data Handling Modeling System (GMDH) model was used to simulate the rainfall-runoff relationship of the catchment, with respect to the observed data during the period of 2008–2009. The statistically downscaled outputs of HadGEM2-ES (Hadley Centre Global Environment Model version 2), general circulation models (GCMs) scenario was used to assess the impacts of climate change on the Gomati River Basin. Future projections were developed for the 2030s, 2040s and 2050s projections, respectively. The results from the present study can contribute to the development of adaptive strategies and future policies for the sustainable management of water resources in North East, Tripura.

0.5 Degree: A Turning point

<p>Although the Caribbean region is considered amongst the most vulnerable to the impacts of climate and climate change, there are very few regional studies or studies matching the regions small scale and size that evaluate or quantify the impacts of these future changes.  The absence becomes even more stark when the long-term temperature goals (LTTGs) of 1.5°C, 2.0°C and 2.5°C above pre-industrial warming levels are considered. By selecting, validating and downscaling a subset of the Hadley Centre’s 17-member Perturbed Physics Ensemble for the Quantifying Uncertainty in Model Predictions (QUMP) project, future changes for both the LTTGs as well as mid and end of century are evaluated, for the entire Caribbean and its six (6) sub-regional zones. Showing distinct and significant sub-regional variations, on average the Caribbean was found to be 2.1°C (>4°C) warmer and 40% (70%) drier by mid-century (end of century). Analysis of the LTTGS shows that the region surpasses lowest target, 1.5 °C, before the end of the 2020’s and experiences progressive warming that spread equatorward as successive thresholds are attained 2.0°C (2030’s) and 2.5°C (2050´s). The far western, the southern and the eastern Caribbean are found to be up to 50% drier at 1.5°C, with intensifications noted for changes at 2.0°C with a reversal of a wet tendency in the north and central Caribbean. The sub-regional variations that exist shows that although the Caribbean lags the globe in its attainment of the LTTGs some of its six subregions are more comparable to the global than the Caribbean mean with the transition from 1.5°C to 2.0°C seeming to represent a turning point for the Caribbean.</p>

ENSO asymmetry: the search for extreme El Niño events in HadGEM

<p>Analysis of a long control run of the Hadley Centre coupled model shows that ENSO asymmetry is weak. We use the same model in our seasonal and decadal prediction systems, and while on seasonal timescales the initialised prediction realistically captures the amplitude of extreme El Niño events, on longer timescales the predictions revert to the control behaviour i.e. there are no very large El Niño events. This may impact on our ability evaluate the risk of extreme regional events. Here we show results exploring asymmetry in both the control model, and also from a number of perturbed parameter experiments, each a plausible realisation of the control.</p>

Extreme climate response to marine cloud brightening in the arid Sahara-Sahel-Arabian Peninsula zone

Purpose Climatic extreme events are predicted to occur more frequently and intensely and will significantly threat the living of residents in arid and semi-arid regions. Therefore, this study aims to assess climatic extremes’ response to the emerging climate change mitigation strategy using a marine cloud brightening (MCB) scheme. Design/methodology/approach Based on Hadley Centre Global Environmental Model version 2-Earth System model simulations of a MCB scheme, this study used six climatic extreme indices [i.e. the hottest days (TXx), the coolest nights (TNn), the warm spell duration (WSDI), the cold spell duration (CSDI), the consecutive dry days (CDD) and wettest consecutive five days (RX5day)] to analyze spatiotemporal evolution of climate extreme events in the arid Sahara-Sahel-Arabian Peninsula Zone with and without MCB implementation. Findings Compared with a Representative Concentration Pathways 4.5 scenario, from 2030 to 2059, implementation of MCB is predicted to decrease the mean annual TXx and TNn indices by 0.4–1.7 and 0.3–2.1°C, respectively, for most of the Sahara-Sahel-Arabian Peninsula zone. It would also shorten the mean annual WSDI index by 118–183 days and the mean annual CSDI index by only 1–3 days, especially in the southern Sahara-Sahel-Arabian Peninsula zone. In terms of extreme precipitation, MCB could also decrease the mean annual CDD index by 5–25 days in the whole Sahara and Sahel belt and increase the mean annual RX5day index by approximately 10 mm in the east part of the Sahel belt during 2030–2059. Originality/value The results provide the first insights into the impacts of MCB on extreme climate in the arid Sahara-Sahel-Arabian Peninsula zone.

Climatology of Borneo Vortices in the HadGEM3-GC31 General Circulation Model

Borneo Vortices (BVs) are intense precipitating winter storms that develop over the equatorial South China Sea and strongly affect the weather and climate over the western Maritime Continent due to their association with deep convection and heavy rainfall. In this study, the ability of the HadGEM3-GC31 (Hadley Centre Global Environment Model 3 - Global Coupled vn. 3.1) global climate model to simulate the climatology of BVs at different horizontal resolutions are examined using an objective feature tracking algorithm. The HadGEM3-GC31 at the N512 ( 25 km) horizontal resolution simulates BVs with well-represented characteristics, including their frequency, spatial distribution and their lower-tropospheric structures when compared with BVs identified in a climate reanalysis, whereas the BVs in the N96 (∼135 km) and N216 (∼65 km) simulations are much weaker and less frequent. Also, the N512 simulation better captures the contribution of BVs to the winter precipitation in Borneo and Malay Peninsula compared with precipitation from a reanalysis data and from observations, while the N96 and N216 simulations underestimate this contribution due to the overly weak low-level convergence of the simulated BVs. The N512 simulation also exhibits an improved ability to reproduce the modulation of BV activity by the occurrence of northeasterly cold surges and active phases of Madden-Julian Oscillation in the region, including increased BV track densities, intensities and lifetimes. A sufficiently high model resolution is thus found to be important to realistically simulate the present-climate precipitation extremes associated with BVs and to study their possible changes in a warmer climate.

Robust observational constraint of uncertain aerosol processes and emissions in a climate model and the effect on aerosol radiative forcing

The effect of observational constraint on the ranges of uncertain physical and chemical process parameters was explored in a global aerosol–climate model. The study uses 1 million variants of the Hadley Centre General Environment Model version 3 (HadGEM3) that sample 26 sources of uncertainty, together with over 9000 monthly aggregated grid-box measurements of aerosol optical depth, PM2.5, particle number concentrations, sulfate and organic mass concentrations. Despite many compensating effects in the model, the procedure constrains the probability distributions of parameters related to secondary organic aerosol, anthropogenic SO2 emissions, residential emissions, sea spray emissions, dry deposition rates of SO2 and aerosols, new particle formation, cloud droplet pH and the diameter of primary combustion particles. Observational constraint rules out nearly 98 % of the model variants. On constraint, the ±1σ (standard deviation) range of global annual mean direct radiative forcing (RFari) is reduced by 33 % to −0.14 to −0.26 W m−2, and the 95 % credible interval (CI) is reduced by 34 % to −0.1 to −0.32 W m−2. For the global annual mean aerosol–cloud radiative forcing, RFaci, the ±1σ range is reduced by 7 % to −1.66 to −2.48 W m−2, and the 95 % CI by 6 % to −1.28 to −2.88 W m−2. The tightness of the constraint is limited by parameter cancellation effects (model equifinality) as well as the large and poorly defined “representativeness error” associated with comparing point measurements with a global model. The constraint could also be narrowed if model structural errors that prevent simultaneous agreement with different measurement types in multiple locations and seasons could be improved. For example, constraints using either sulfate or PM2.5 measurements individually result in RFari±1σ ranges that only just overlap, which shows that emergent constraints based on one measurement type may be overconfident.

Long-Term Impacts of Partial Afforestation on Water and Salt Dynamics of an Intermittent Catchment under Climate Change

Soil salinization is a major environmental issue in arid and semi-arid regions, and has been accelerated in some areas by removal of native vegetation cover. Partial afforestation can be a practical mitigation strategy if efficiently integrated with farms and pastures. Using an integrated surface-subsurface hydrological model, this study evaluates the water and salt dynamics and soil salinization conditions of a rural intermittent catchment in the semi-arid climate of southeast Australia subjected to four different partial afforestation configurations under different climate change scenarios, as predicted by several general circulation models. The results show that the locations of afforested areas can induce a retarding effect in the outflow of groundwater salt, with tree planting at lower elevations showing the steadier salt depletion rates. Moreover, except for the configuration with trees planted near the outlet of the catchment, the streamflow is maintained under all other configurations. It appears that under both Representative Concentration Pathways considered (RCP 4.5 and RCP 8.5), the Hadley Centre Global Environmental Model represents the fastest salt export scheme, whereas the Canadian Earth System Model and the Model for Interdisciplinary Research on Climate represent the slowest salt export scheme. Overall, it is found that the location of partial afforestation generally plays a more significant role than the climate change scenarios.