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Mark Ringer

University of Reading, Meteorology, Alumnus

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Papers by Mark Ringer

Robustness, uncertainties, and emergent constraints in the radiative responses of stratocumulus cloud regimes to future warming

analysis of the bulk in-regime albedo. Furthermore we find that the inter-model difference in the... more analysis of the bulk in-regime albedo. Furthermore we find that the inter-model difference in the sign of the in-cloud albedo feedback is consistent with the difference in sign of the in-cloud liquid water path response, and there is a strong positive correlation between the in-regime liquid water path in the control climate and its response to warming. We therefore conclude that further breakdown of the in-regime properties into cloud cover and in-cloud properties is necessary to better understand the behavior of the stratocumulus regime. Since cloud water is a physical property and is independent of a model's radiative assumptions, it could potentially provide a useful emergent constraint on cloud feedback. Keywords Stratocumulus · Liquid water path · Cloud feedback · Cloud radiative effect · Climate model

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

Climate Dynamics, 2015

The impacts of a hypothetical slowdown in the Atlantic Meridional 1 Overturning Circulation (AMOC... more The impacts of a hypothetical slowdown in the Atlantic Meridional 1 Overturning Circulation (AMOC) are assessed in a state-of-the-art global climate 2 model (HadGEM3), with particular emphasis on Europe. This is the highest reso-3 lution coupled global climate model to be used to study the impacts of an AMOC 4 slowdown so far. Many results found are consistent with previous studies and can 5 be considered robust impacts from a large reduction or collapse of the AMOC. 6 These include: widespread cooling throughout the North Atlantic and northern 7 hemisphere in general; less precipitation in the northern hemisphere midlatitudes; 8 large changes in precipitation in the tropics and a strengthening of the North 9

Global-mean radiative feedbacks and forcing in atmosphere-only and coupled atmosphere- ocean climate change experiments

Analysis of the available Coupled Model Intercomparison Project Phase 5 models suggests that sea ... more Analysis of the available Coupled Model Intercomparison Project Phase 5 models suggests that sea surface temperature-forced, atmosphere-only global warming experiments (" amip4K, " " amipFuture, " and " aqua4K ") are a good guide to the global cloud feedbacks determined from coupled atmosphere-ocean CO 2-forced simulations, including the intermodel spread. Differences in the total climate feedback parameter between the experiments arise primarily from differences in the clear-sky feedbacks which can largely be anticipated from the nature of the experimental design. The effective CO 2 radiative forcing is anticorrelated with the total feedback in the coupled simulations. This anticorrelation strengthens as the experimental design becomes simpler, the number of potential degrees of freedom of the system's response reduces, and the relevant physical processes can be identified. In the aquaplanet simulations the anticorrelation is primarily driven by opposing changes in the rapid cloud adjustment to CO 2 and the net cloud response to increased surface warming. Establishing a physical explanation for this behavior is important future work.

Cloud Feedbacks, Rapid Adjustments, and the Forcing–Response Relationship in a Transient CO 2 Reversibility Scenario

The Hadley Centre Global Environment Model, version 2–Earth System (HadGEM2-ES) climate model is ... more The Hadley Centre Global Environment Model, version 2–Earth System (HadGEM2-ES) climate model is forced by a 1% yr 21 compound increase in atmospheric CO 2 for 140 years, followed by a 1% yr 21 CO 2 decrease back to the starting level. Analogous atmosphere-only simulations are performed to diagnose the component of change associated with the effective radiative forcing and rapid adjustments. The residual change is associated with radiative feedbacks that are shown to be linearly related to changes in global-mean surface air temperature and are found to be reversible under this experimental design, even for regional cloud feedback changes. The cloud adjustment is related to changes in cloud amount, with little indication of any large-scale changes in cloud optical depth. Plant physiological forcing plays a significant role in determining the cloud adjustment in this model and is the dominant contribution to the low-level cloud changes over land. Low-level cloud adjustments are associated with changes in surface turbulent fluxes and lower tropospheric stability, with significant adjustments in boundary layer cloud types and in the depth of the boundary layer itself. The linearity of simple forcing–response frameworks are examined and found to be generally applicable. Small regional departures from linearity occur during the early part of the ramp-down phase, where the Southern Ocean and eastern tropical Pacific continue to warm for a few decades, despite the reversal in radiative forcing and global temperatures. The importance of considering time-varying patterns of warming and regional phenomena when diagnosing and understanding feedbacks in a coupled atmosphere–ocean framework is highlighted.

Sensitivity of an Earth system climate model to idealized radiative forcing

Geophysical Research Letters, 2012

Reversibility in an Earth System model in response to CO 2 concentration changes

Environmental Research Letters, 2012

We use the HadGEM2-ES Earth System model to examine the degree of reversibility of a wide range o... more We use the HadGEM2-ES Earth System model to examine the degree of reversibility of a wide range of components of the Earth System under idealized climate change scenarios where the atmospheric CO2 concentration is gradually increased to four times the pre-industrial level and then reduced at a similar rate from several points along this trajectory. While some modelled quantities respond

Interannual variabilty of the earths radiation budget: some regional studies

Int J Climatol, 1997

A detailed study is presented of the interannual variability of the Earths radiation budget (ERB)... more A detailed study is presented of the interannual variability of the Earths radiation budget (ERB) at the top of the atmosphere in three equatorial regions: the western Pacific over Indonesia, the eastern Pacific off the west coast of South America and the eastern Atlantic off the west coast of Africa. The objective is to try and understand the cloud, surface and ERB interactions that occur in these areas, each of which shows a large interannual signal in the net radiation balance. The period studied extends from March 1979 through to April 1985, for which coincident ERB and cloud data are available from the Nimbus-7 ERB and Cloud Climatology data sets. This period encompasses the exceptional 1982-1983 ENSO as well as the 1984 Atlantic warming event. Additionally, sea-surface temperature data from the Global Ocean Surface Temperature Atlas (GOSTA) data set are used in combination with the ERB data to partition the outgoing longwave radiation into surface emission and greenhouse-effect components. The methodology involves examination of the time series of anomalies in all of these quantities together with the formulation of statistical relationships amongst them. These methods firstly allow the shortwave (SW) and longwave (LW) components of the ERB anomalies to be identified. The SW and LW anomalies are themselves seen to be made up of different components and, much like the net balance, are often the residuals of two competing effects. This is exemplified in the eastern Pacific and Atlantic regions, which both experienced periods of anomalously high SSTs. In such areas the SW anomaly can arise due to an imbalance between the cooling effect of increased high cloudiness and warming due to reduction of low level cloud, whilst the LW anomaly is composed of warming due to the increase in high cloud amount and cooling due to increased surface emission. The result is that anomalies in the net balance term, which is ultimately the most important with regard to climate variability, are seen to arise as a result of complex interactions between the atmosphere, cloudiness and surface.

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 last thirty years, as a significant and timely contribution to the ECV databases required by UNFCCC". In particular, the CCI programme aims to deliver a set of "Global Satellite Data Products" as a contribution to the establishment of a long-term Climate Data Record meeting the needs of the Global Climate Observing System (GCOS). Within the first phase, the CCI will focus on the following sub-set of eleven "Essential Climate Variable" (ECVs) defined by GCOS. For the oceans the ECVs identified are Sea-Ice, Sea-Level, Sea-Surface Temperature and Ocean Colour. For the land surface Glaciers & Ice caps, Land Cover and Fire Disturbance were selected. Finally for the atmospheric domain Cloud Properties, Ozone, Aerosols and Greenhouse Gases were selected. In addition to the individual projects addressing each ECV a Climate Modelling Users Group (CMUG) is being set up. The role of the CMUG is to bring a climate modellers perspective to the programme and to enable the satellite data community and the "Climate Modelling Community" to work closely together. Another important task is to provide the role of integration across the 11 diverse ECV projects. This presentation will describe the ESA CCI and the role of the CMUG and invite the climate modellers to provide their requirements to the CMUG.

Evaluation of cloud systems in the Met Office global forecast model using CloudSat data

Clouds and their radiative properties are still not sufficiently well represented in numerical we... more Clouds and their radiative properties are still not sufficiently well represented in numerical weather prediction (NWP) and climate models. Improving their representation is a key priority, as clouds play a main role in the Earth's radiation budget and are a key uncertainty in predictions of climate change. CloudSat is the first spaceborne millimetre wavelength radar (94 GHz) that provides estimates of cloud condensate and precipitation globally. We have developed a system to simulate CloudSat data in the Met Office Unified Model (MetUM) that is consistent with the observations. We apply this simulator to evaluate the MetUM global forecast model, as previous studies have shown that the global forecast model is a useful framework in which to analyse cloud representation errors that are relevant for both numerical weather prediction and climate time scales. These comparisons are presented from two different points of view. Firstly, we analyse the direct comparisons of CloudSat passes over a mid-latitude system and tropical convection. Secondly, a more statistically-based approach is followed by computing two dimensional height-reflectivity histograms integrated over time. This second approach allows us to study how well the vertical distribution of clouds is represented in the Me-tUM.

Interannual variability of the Earth's radiation budget and cloudiness: a satellite view

Thesis (Ph. D.)--University of Reading, 1994.

Using ERA40 products to verify and improve the Met Office climate model

Evaluation of Tropical Convection Regimes in the HadGEM2 Model Using Radio Occultation Observations

ABSTRACT The evaluation of Global Climate Models (GCMs) requires high-quality observational data ... more ABSTRACT The evaluation of Global Climate Models (GCMs) requires high-quality observational data sets. Global Positioning System (GPS) Radio Occultation (RO) measurements, which are available continuously from various satellite missions since 2001, provide a global and independent data record for the upper troposphere and lower stratosphere (UTLS). The measurements are based on precise atomic clocks and feature long-term stability, homogeneity, and accuracy. Best data quality is achieved at about 5 km to 30 km altitude and observational errors are well characterized. Profiles of key climate variables, such as refractivity, pressure, geopotential height, and temperature, are retrieved at a high vertical resolution of about 0.5 km in the troposphere to 1.5 km in the stratosphere. Due to these characteristics, RO qualifies as climate benchmark data type, which can be used for the evaluation of climate models. In this presentation we focus on physical processes relevant to tropical water vapor/lapse rate feedback. Water vapor and lapse rate responses are closely coupled in the upper troposphere and models with larger negative lapse rate feedback also have a larger positive water vapor feedback. We show first results on the representation of UTLS temperature lapse rates and refractivity gradients in RO observations and in Met Office Hadley Centre HadGEM2 model data. To allow a consistent and process-oriented approach, we classify moist and dry tropical regimes through distinction between dynamical up- and downdraft regions. The pressure vertical velocity at 500 hPa (ω500) and surface temperature (T) from ERA-Interim (for RO profiles) and from the HadGEM2 model itself (for the model) is used for the classification of these regimes. RO data and co-located HadGEM2 model profiles are sorted and sampled into vertical velocity classes and a systematic comparison is performed. A better insight into observation and model behavior in tropical convection regimes will contribute to the development of improved model parameterizations.

Evaluating the cloud response to climate change and current climate variability

The radiative feedback from clouds remains one of the largest uncertainties in determining the cl... more The radiative feedback from clouds remains one of the largest uncertainties in determining the climate sensitivity to increasing greenhouse gas (GHG) concentrations. This study presents a diagnostic method of evaluating the simulated tropical cloud response to climate change. The method is illustrated by comparing the effect on the climate response of several new developments to the Meteorological Office's Hadley Centre atmosphere model coupled to a mixedlayer ocean. It is shown that the cloud response over tropical oceans to a doubling of CO 2 at individual locations appears to depend more upon the change in vertical velocity and whether the sea surface warms more or less than the tropical mean, rather than the absolute value of the surface temperature. By using compositing techniques, the model cloud response to doubling CO 2 is related to the model cloud response to present-day spatio-temporal sea surface temperature anomalies. The use of special model diagnostics to take account of cloud overlap assumptions allows comparison of the modelled present-day variability with satellite data to evaluate the cloud response. Based upon this evaluation, it is possible to identify which of the new physical schemes are likely to provide a more reliable cloud response in the climate change simulation. It is found that overall, the model developments improve the simulation of present-day cloud processes and, through the relation with the climate change simulation, we may have more confidence in the cloud response to increasing GHGs occurring via these processes.

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

Diagnosis of regime-dependent cloud simulation errors in CMIP5 models using “A-Train” satellite observations and reanalysis data

Journal of Geophysical Research: Atmospheres, 2013

1] The vertical distributions of cloud water content (CWC) and cloud fraction (CF) over the tropi... more 1] The vertical distributions of cloud water content (CWC) and cloud fraction (CF) over the tropical oceans, produced by 13 coupled atmosphere-ocean models submitted to the Phase 5 of Coupled Model Intercomparison Project (CMIP5), are evaluated against CloudSat/CALIPSO observations as a function of large-scale parameters. Available CALIPSO simulator CF outputs are also examined. A diagnostic framework is developed to decompose the cloud simulation errors into large-scale errors, cloud parameterization errors and covariation errors. We find that the cloud parameterization errors contribute predominantly to the total errors for all models. The errors associated with large-scale temperature and moisture structures are relatively greater than those associated with large-scale midtropospheric vertical velocity and lower-level divergence. All models capture the separation of deep and shallow clouds in distinct large-scale regimes; however, the vertical structures of high/low clouds and their variations with large-scale parameters differ significantly from the observations. The CWCs associated with deep convective clouds simulated in most models do not reach as high in altitude as observed, and their magnitudes are generally weaker than CloudSat total CWC, which includes the contribution of precipitating condensates, but are close to CloudSat nonprecipitating CWC. All models reproduce maximum CF associated with convective detrainment, but CALIPSO simulator CFs generally agree better with CloudSat/CALIPSO combined retrieval than the model CFs, especially in the midtroposphere. Model simulated low clouds tend to have little variation with large-scale parameters except lower-troposphere stability, while the observed low cloud CWC, CF, and cloud top height vary consistently in all large-scale regimes. Citation: Su, H., et al. (2013), Diagnosis of regime-dependent cloud simulation errors in CMIP5 models using "A-Train" satellite observations and reanalysis data,

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

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

uncertainty improved resolution, complexity and dealing with capability: the competing requiremen... more

Evaluating climate model simulations of tropical cloud

Tellus A, 2004

A B S T R A C T The representation of tropical cloud and its radiative effects in the Hadley Cent... more A B S T R A C T The representation of tropical cloud and its radiative effects in the Hadley Centre climate model are evaluated using a combination of Earth observation data and meteorological reanalyses. It is shown that useful information regarding the model's physical parametrizations can be obtained by considering cloud radiative effects and cloud types in terms of 'dynamical regimes', defined in terms of sea surface temperature and large-scale vertical motion. In addition to comparisons with observed top-of-atmosphere radiation budget parameters and total cloud amount, information is obtained through direct comparisons of International Satellite Cloud Climatology Project (ISCCP) cloud types, defined according to cloud top pressure and optical depth, with corresponding model diagnostics. An analysis of the atmosphereonly model, HadAM3, demonstrates how errors in the albedo and outgoing long-wave radiation can be related to the simulation of particular cloud types in the different dynamical regimes. Inconsistencies between the simulations of the various cloud types and the top-of-atmosphere radiation budget are also highlighted. A version of the model including several new cloud-related parametrizations is then examined. A more consistent comparison with the observed radiation budget and cloud amounts is obtained, although deficiencies in the simulation still remain. A parametrization for the radiative effects of convective anvils and the impact of a new boundary layer mixing scheme are examined in more detail. Finally, it is shown how the climate model's ability to simulate the observed interannual variability of cloud in the equatorial Pacific follows directly from the analysis according to dynamical regimes.

Evaluation of Climate-Model Simulations of Hirs Water-Vapour Channel Radiances

Simulation of satellite channel radiances in the Met Office Unified Model

Quarterly Journal of the Royal Meteorological Society, 2003

A system is described which allows satellite channel radiances to be simulated within both the nu... more A system is described which allows satellite channel radiances to be simulated within both the numerical weather prediction and climate versions of the Met Office Unified Model. It is based on a spherical harmonics version of the radiation code that calculates radiative fluxes and heating rates in the climate model and it uses the same pre-processing software and molecular absorption database. In the results shown here, fractional cloud cover is represented by decomposition into separate columns. The methodology is described and results of offline tests of the code against high spectral resolution calculations are presented. Examples of infrared window and water vapour channel brightness temperatures simulated using the global forecast model are then compared with Meteosat 7 imagery. The utility of radiance simulations for model validation studies is illustrated by these comparisons, and other applications are also discussed.

Evaluation of moisture in the Hadley Centre climate model using simulations of HIRS water-vapour channel radiances

Quarterly Journal of the Royal Meteorological Society, 2003

It is important to establish that climate models can accurately simulate the observed present-day... more It is important to establish that climate models can accurately simulate the observed present-day uctuations of water vapour. In particular, water-vapour and cloud-radiative feedbacks are intrinsically linked to processes governing relative-humidity distribution and variability. To explore these issues, clear-sky radiances, sensitive to upper-tropospheric relative humidity, are simulated within the Hadley Centre atmospheric climate model, version HadAM3, allowing direct comparison with High Resolution Infrared Sounder (HIRS) observations. The model is forced by observed sea surface temperatures and sea-ice elds over the period 1979-98. Evaluation of the simulated distribution and variability of water vapour is undertaken utilizing the HIRS 6.7 m brightness temperature ( 6 7 ) and satellite measurements of column-integrated water vapour and clear-sky outgoing longwave radiation (OLR). Modi cations are made to the clear-sky OLR and 6 7 HadAM3 diagnostics to reduce sampling inconsistencies with the observed products. Simulated 6 7 over subtropical dry zones are higher than 6 7 from observations, particularly in the southern hemisphere, and is symptomatic of an overactive circulation. The observed spatial signature of the 6 7 interannual variability is dominated by El Niño and is captured well by HadAM3. Interannual variability of the tropical ocean mean 6 7 is consistent between HadAM3 and the HIRS observations, suggesting that the small simulated decadal changes in relative humidity are realistic.