M. Ringer

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Papers by M. Ringer

Impact of changing convection scheme on cloud feedbacks in the tropics

The ESA Climate Change Initiative - Climate Modellers User Group

The new ESA Climate Change Initiative (CCI) approved in 2009 is in the process of being set up. T... more The new ESA Climate Change Initiative (CCI) approved in 2009 is in the process of being set up. The overall objective of the CCI, as laid out in the Programme declaration approved by ESA member states is: "To realize the full potential of the long-term global "Earth Observation" archives that ESA together with its Member states have established over the

Observations of Changes In Marine Boundary Layer Clouds

EUMETSAT Meteorological …, 2009

Barber, C.R., Allan, R.P. and Ringer, M. (2009) Observations of changes in marine boundary layer ... more

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Global and European climate impacts of a slowdown of the AMOC in a high resolution GCM

Climate Dynamics, 2015

ABSTRACT The impacts of a hypothetical slowdown in the Atlantic Meridional Overturning Circulatio... more ABSTRACT The impacts of a hypothetical slowdown in the Atlantic Meridional Overturning Circulation (AMOC) are assessed in a state-of-the-art global climate model (HadGEM3), with particular emphasis on Europe. This is the highest resolution coupled global climate model to be used to study the impacts of an AMOC slowdown so far. Many results found are consistent with previous studies and can be considered robust impacts from a large reduction or collapse of the AMOC. These include: widespread cooling throughout the North Atlantic and northern hemisphere in general; less precipitation in the northern hemisphere midlatitudes; large changes in precipitation in the tropics and a strengthening of the North Atlantic storm track. The focus on Europe, aided by the increase in resolution, has revealed previously undiscussed impacts, particularly those associated with changing atmospheric circulation patterns. Summer precipitation decreases (increases) in northern (southern) Europe and is associated with a negative summer North Atlantic Oscillation signal. Winter precipitation is also affected by the changing atmospheric circulation, with localised increases in precipitation associated with more winter storms and a strengthened winter storm track. Stronger westerly winds in winter increase the warming maritime effect while weaker westerlies in summer decrease the cooling maritime effect. In the absence of these circulation changes the cooling over Europe&#39;s landmass would be even larger in both seasons. The general cooling and atmospheric circulation changes result in weaker peak river flows and vegetation productivity, which may raise issues of water availability and crop production.

Using A-Train satellite observations to diagnosis and improve cloud and water vapor simulations in post-CMIP5 climate models

The Met Office Hadley Centre climate modelling capability: the competing requirements for improved resolution, complexity and dealing with uncertainty

by M. Ringer and S. Woodward

Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2007

Predictions of future climate change require complex computer models of the climate system to rep... more Predictions of future climate change require complex computer models of the climate system to represent the full range of processes and interactions that influence climate. The Met Office Hadley Centre uses &#39;families&#39; of models as part of the Met Office Unified Model Framework to address different classes of problems. The HadGEM family is a suite of state-of-the-art global environment models that are used to reduce uncertainty and represent and predict complex feedbacks. The HadCM3 family is a suite of well established but cheaper models that are used for multiple simulations, for example, to quantify uncertainty or to test the impact of multiple emissions scenarios.

Evaluating cloud systems in the Met Office global forecast model using simulated CloudSat radar reflectivities

by M. Ringer and Sean F Milton

Journal of Geophysical Research, 2008

1] CloudSat radar reflectivities are simulated in the Met Office global forecast model in a manne... more 1] CloudSat radar reflectivities are simulated in the Met Office global forecast model in a manner which is consistent with the CloudSat observations. The method is described and applied in an evaluation study of the model's performance over the period December 2006 to February 2007. The study uses both statistical and case study approaches and examines the model's simulation of cloud systems globally and in three regions of contrasting weather and cloud regimes: the tropical warm pool, the North Atlantic Ocean, and the stratocumulus region off the west coast of California. In general, the model shows a good representation of the vertical structure of clouds systems, although a lack of midlevel cloud is ubiquitous. The model shows a nondrizzling cloud mode and a clearly separated drizzling mode that is not seen in the observations, independent of the geographical region. The comparisons suggest that the intensity of drizzle is too high, confirming on a global basis what recent ground-based measurements have also shown. They also suggest that the parameterization of ice cloud fraction as a monotonic function of the grid box mean ice water content is not consistent with the observations. Evaluating cloud systems in the Met Office global forecast model using simulated CloudSat radar reflectivities,

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The Physical Properties of the Atmosphere in the New Hadley Centre Global Environmental Model (HadGEM1). Part I: Model Description and Global Climatology

Journal of Climate, 2006

Abstract The atmospheric component of the new Hadley Centre Global Environmental Model (HadGEM1) ... more

Global mean cloud feedbacks in idealized climate change experiments

Geophysical Research Letters, 2006

Global mean cloud feedbacks in ten atmosphere-only climate models are estimated in perturbed sea ... more Global mean cloud feedbacks in ten atmosphere-only climate models are estimated in perturbed sea surface temperature (SST) experiments and the results compared to doubled CO2 experiments using mixed-layer ocean versions of these same models. The cloud feedbacks in any given model are generally not consistent: the sign of the net cloud radiative feedback may vary according to the experimental design.

Sensitivity of the Earth's radiation budget to interannual variations in cloud amount

Climate Dynamics, 1997

Using two pairs of coincident long-term satellite derived cloud and earth radiation budget data s... more Using two pairs of coincident long-term satellite derived cloud and earth radiation budget data sets (Nimbus-7 ERB/Nimbus-7 Cloud Climatology and ERBE Scanner/ISCCP-C2), estimates are made of the sensitivity of the top of the atmosphere radiation budget to interannual variations in the total cloud amount. Both sets of analyses indicate that the largest net warming due to interannual cloud cover changes occurs over desert regions, while the largest net cooling occurs in areas of persistent marine stratiform cloud. There is generally a large amount of cancellation between the large shortwave cooling and longwave warming effects in tropical convection regions. However, the Nimbus-7 analysis identifies an area of net warming in the tropical eastern Pacific Ocean which is shown to be associated with the 1982-83 ENSO event. In the zonal mean the Nimbus-7 data sets indicate that interannual cloud cover changes lead to a net warming at low latitudes and net cooling polewards of 25°in both hemispheres. In contrast, the analysis of the ERBE and ISCCP data sets indicates net cooling everywhere except for the Northern Hemisphere equatorwards of 20°N. For the spatial average between 60°N and 60°S the ratio of the shortwave and longwave effects is 0.94 in the Nimbus-7 analysis (i.e. clouds cause a small net warming) and 1.21 in the ERBE-ISCCP analysis (i.e. a net cooling). Given their improved spatial and temporal sampling the analysis using the ERBE and ISCCP data sets should be the more reliable. However, the large differences between the two analyses still raises some issues concerning the confidence with which the sign of the effect of clouds on the radiation budget at these time scales is currently known.

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On the contribution of local feedback mechanisms to the range of climate sensitivity in two GCM ensembles

by M. Ringer and T. Ogura

Climate Dynamics, 2006

Global and local feedback analysis techniques have been applied to two ensembles of mixed layer e... more Global and local feedback analysis techniques have been applied to two ensembles of mixed layer equilibrium CO 2 doubling climate change experiments, from the CFMIP (Cloud Feedback Model Intercomparison Project) and QUMP (Quantifying Uncertainty in Model Predictions) projects. Neither of these new ensembles shows evidence of a statistically significant change in the ensemble mean or variance in global mean climate sensitivity when compared with the results from the mixed layer models quoted in the Third Assessment Report of the IPCC. Global mean feedback analysis of these two ensembles confirms the large contribution made by inter-model differences in cloud feedbacks to those in climate sensitivity in earlier studies; net cloud feedbacks are responsible for 66% of the inter-model variance in the total feedback in the CFMIP ensemble and 85% in the QUMP ensemble. The ensemble mean global feedback components are all statistically indistinguishable between the two ensembles, except for the clear-sky shortwave feedback which is stronger in the CFMIP ensemble. While ensemble variances of the shortwave cloud feedback and both clear-sky feedback terms are larger in CFMIP, there is considerable overlap in the cloud feedback ranges; QUMP spans 80% or more of the CFMIP ranges in longwave and shortwave cloud feedback. We introduce a local cloud feedback classification system which distinguishes different types of cloud feedbacks on the basis of the relative strengths of their longwave and shortwave components, and interpret these in terms of responses of different cloud types diagnosed by the International Satellite Cloud Climatology Project simulator. In the CFMIP ensemble, areas where low-top cloud changes constitute the largest cloud response are responsible for 59% of the contribution from cloud feedback to the variance in the total feedback. A similar figure is found for the QUMP ensemble. Areas of positive low cloud feedback (associated with reductions in low level cloud amount) contribute most to this figure in the CFMIP ensemble, while areas of negative cloud feedback (associated with increases in low level cloud amount and optical thickness) contribute most in QUMP. Classes associated with high-top cloud feedbacks are responsible for 33 and 20% of the cloud feedback contribution in CFMIP and QUMP, respectively, while classes where no particular cloud type stands out are responsible for 8 and 21%.

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Recent Studies on Tropical Cloudiness

The Geostationary Earth Radiation Budget (Gerb) Experiment: Science and Applications

Cloud liquid water path and radiative feedbacks over the Southern Ocean

by Ambarish Karmalkar and M. Ringer

Climate models show a robust shortwave negative feedback in the midlatitude oceans in climate cha... more Climate models show a robust shortwave negative feedback in the midlatitude oceans in climate change simulations. This feedback is commonly attributed to an increase in cloud optical depth due to ice to liquid phase change as the climate warms. Here we use a cyclone compositing technique to show that the models' cloud liquid water path (LWP) response is strongly dependent on cloud regime. The radiative and LWP responses are not as tightly coupled as a zonal-mean analysis would suggest, implying that the physical mechanisms that control the overall LWP response are not necessarily responsible for the radiative response. The area of the cyclone dominated by low-level stratiform and shallow convective clouds plays a dominant role in the radiative response. Since these are mostly supercooled liquid clouds, the strength of a negative cloud phase feedback in the real world should be smaller than the one predicted by current models.

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