152 results found
Misios S, Gray LJ, Knudsen MF, et al., 2019, Slowdown of the Walker circulation at solar cycle maximum., Proc Natl Acad Sci U S A
The Pacific Walker Circulation (PWC) fluctuates on interannual and multidecadal timescales under the influence of internal variability and external forcings. Here, we provide observational evidence that the 11-y solar cycle (SC) affects the PWC on decadal timescales. We observe a robust reduction of east-west sea-level pressure gradients over the Indo-Pacific Ocean during solar maxima and the following 1-2 y. This reduction is associated with westerly wind anomalies at the surface and throughout the equatorial troposphere in the western/central Pacific paired with an eastward shift of convective precipitation that brings more rainfall to the central Pacific. We show that this is initiated by a thermodynamical response of the global hydrological cycle to surface warming, further amplified by atmosphere-ocean coupling, leading to larger positive ocean temperature anomalies in the equatorial Pacific than expected from simple radiative forcing considerations. The observed solar modulation of the PWC is supported by a set of coupled ocean-atmosphere climate model simulations forced only by SC irradiance variations. We highlight the importance of a muted hydrology mechanism that acts to weaken the PWC. Demonstration of this mechanism acting on the 11-y SC timescale adds confidence in model predictions that the same mechanism also weakens the PWC under increasing greenhouse gas forcing.
Ball WT, Rozanov EV, Alsing J, et al., 2019, The upper stratospheric solar cycle ozone response, Geophysical Research Letters, Vol: 46, Pages: 1831-1841, ISSN: 0094-8276
The solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1–10 hPa) zonally averaged spatial responses; this and the recommended data set for comparison remains disputed. Recent data-merging advancements have led to more robust observational data. Using these data, we show that the observed SC signal exhibits an upper stratosphere U-shaped spatial structure with lobes emanating from the tropics (5–10 hPa) to high altitudes at midlatitudes (1–3 hPa). We confirm this using two independent chemistry climate models in specified dynamics mode and an idealized timeslice experiment. We recommend the BASIC v2 ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used.
Nowack P, Ong QYE, Braesicke P, et al., Machine learning parameterizations for ozone in climate sensitivity simulations, Kurzfassungen der Meteorologentagung DACH
Nowack PJ, Braesicke P, Haigh J, et al., 2018, Using machine learning to build temperature-based ozone parameterizations for climate sensitivity simulations, Environmental Research Letters, Vol: 13, ISSN: 1748-9326
A number of studies have demonstrated the importance of ozone in climate change simulations, for example concerning global warming projections and atmospheric dynamics. However, fully interactive atmospheric chemistry schemes needed for calculating changes in ozone are computationally expensive. Climate modelers therefore often use climatological ozone fields, which are typically neither consistent with the actual climate state simulated by each model nor with the specific climate change scenario. This limitation applies in particular to standard modeling experiments such as preindustrial control or abrupt 4xCO2 climate sensitivity simulations. Here we suggest a novel method using a simple linear machine learning regression algorithm to predict ozone distributions for preindustrial and abrupt 4xCO2 simulations. Using the atmospheric temperature field as the only input, the regression reliably predicts three-dimensional ozone distributions at monthly to daily time intervals. In particular, the representation of stratospheric ozone variability is much improved compared with a fixed climatology, which is important for interactions with dynamical phenomena such as the polar vortices and the Quasi-Biennial Oscillation. Our method requires training data covering only a fraction of the usual length of simulations and thus promises to be an important stepping stone towards a range of new computationally efficient methods to consider ozone changes in long climate simulations. We highlight key development steps to further improve and extend the scope of machine learning-based ozone parameterizations.
Ball WT, Alsing J, Mortlock DJ, et al., 2018, Continuous decline in lower stratospheric ozone offsets ozone layer recovery, Atmospheric Chemistry and Physics Discussions, Vol: 18, Pages: 1379-1394, ISSN: 1680-7367
Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the Brewer–Dobson circulation (BDC), forming a protective "ozone layer" around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol, and since 1998 ozone in the upper stratosphere is rising again, likely the recovery from halogen-induced losses. Total column measurements of ozone between the Earth's surface and the top of the atmosphere indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes between 60°S and 60°N outside the polar regions (60–90°). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60°S and 60°N has indeed continued to decline since 1998. We find that, even though upper stratospheric ozone is recovering, the continuing downward trend in the lower stratosphere prevails, resulting in a downward trend in stratospheric column ozone between 60°S and 60°N. We find that total column ozone between 60°S and 60°N appears not to have decreased only because of increases in tropospheric column ozone that compensate for the stratospheric decreases. The reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established.
Ball WT, Alsing J, Mortlock DJ, et al., 2018, Evidence for a continuous decline in lower stratospheric ozone offsetting ozone layer recovery, Atmospheric Chemistry and Physics, Vol: 18, Pages: 1379-1394, ISSN: 1680-7316
Ozone forms in the Earth's atmosphere from the photodissociation of molecular oxygen, primarily in the tropical stratosphere. It is then transported to the extratropics by the Brewer–Dobson circulation (BDC), forming a protective "ozone layer" around the globe. Human emissions of halogen-containing ozone-depleting substances (hODSs) led to a decline in stratospheric ozone until they were banned by the Montreal Protocol, and since 1998 ozone in the upper stratosphere is rising again, likely the recovery from halogen-induced losses. Total column measurements of ozone between the Earth's surface and the top of the atmosphere indicate that the ozone layer has stopped declining across the globe, but no clear increase has been observed at latitudes between 60° S and 60° N outside the polar regions (60–90°). Here we report evidence from multiple satellite measurements that ozone in the lower stratosphere between 60° S and 60° N has indeed continued to decline since 1998. We find that, even though upper stratospheric ozone is recovering, the continuing downward trend in the lower stratosphere prevails, resulting in a downward trend in stratospheric column ozone between 60° S and 60° N. We find that total column ozone between 60° S and 60° N appears not to have decreased only because of increases in tropospheric column ozone that compensate for the stratospheric decreases. The reasons for the continued reduction of lower stratospheric ozone are not clear; models do not reproduce these trends, and thus the causes now urgently need to be established.
Ball WT, Alsing J, Mortlock DJ, et al., 2017, Reconciling differences in stratospheric ozone composites, Atmospheric Chemistry and Physics, Vol: 17, Pages: 12269-12302, ISSN: 1680-7316
Observations of stratospheric ozone from multipleinstruments now span three decades; combining these intocomposite datasets allows long-term ozone trends to be estimated.Recently, several ozone composites have been published,but trends disagree by latitude and altitude, even betweencomposites built upon the same instrument data. Weconfirm that the main causes of differences in decadal trendestimates lie in (i) steps in the composite time series when theinstrument source data changes and (ii) artificial sub-decadaltrends in the underlying instrument data. These artefacts introducefeatures that can alias with regressors in multiple linearregression (MLR) analysis; both can lead to inaccuratetrend estimates. Here, we aim to remove these artefacts usingBayesian methods to infer the underlying ozone time seriesfrom a set of composites by building a joint-likelihoodfunction using a Gaussian-mixture density to model outliersintroduced by data artefacts, together with a data-driven prioron ozone variability that incorporates knowledge of problemsduring instrument operation. We apply this Bayesianself-calibration approach to stratospheric ozone in 10◦ bandsfrom 60◦ S to 60◦ N and from 46 to 1 hPa (∼ 21–48 km) for1985–2012. There are two main outcomes: (i) we independentlyidentify and confirm many of the data problems previouslyidentified, but which remain unaccounted for in existingcomposites; (ii) we construct an ozone composite, withuncertainties, that is free from most of these problems – wecall this the BAyeSian Integrated and Consolidated (BASIC)composite. To analyse the new BASIC composite, we usedynamical linear modelling (DLM), which provides a morerobust estimate of long-term changes through Bayesian inferencethan MLR. BASIC and DLM, together, provide astep forward in improving estimates of decadal trends. Ourresults indicate a significant recovery of ozone since 1998 inthe upper stratosphere, of both northern and southern midlatitudes,in all f
Geen R, Czaja A, Haigh JD, 2016, The effects of increasing humidity on heat transport by extratropical waves, Geophysical Research Letters, Vol: 43, Pages: 8314-8321, ISSN: 1944-8007
This study emphasizes the separate contributions of the warm and cold sectors of extratropical cyclones to poleward heat transport. Aquaplanet simulations are performed with an intermediate complexity climate model in which the response of the atmosphere to a range of values of saturation vapor pressure is assessed. These simulations reveal stronger poleward transport of latent heat in the warm sector as saturation vapor pressure is increased and an unexpected increase in poleward sensible heat transport in the cold sector. The latter results nearly equally from changes in the background stability of the atmosphere at low levels and changes in the temporal correlation between wind and temperature fields throughout the troposphere. Increased stability at low level reduces the likelihood that movement of cooler air over warmer water results in an absolutely unstable temperature profile, leading to less asymmetric damping of temperature and meridional velocity anomalies in cold and warm sectors.
Dhomse SS, Chipperfield MP, Damadeo RP, et al., 2016, On the ambiguous nature of the 11 year solar cycle signal in upper stratospheric ozone, Geophysical Research Letters, Vol: 43, Pages: 7241-7249, ISSN: 1944-8007
Up to now our understanding of the 11 year ozone solar cycle signal (SCS) in the upper stratosphere has been largely based on the Stratospheric Aerosol and Gas Experiment (SAGE) II (v6.2) data record, which indicated a large positive signal which could not be reproduced by models, calling into question our understanding of the chemistry of the upper stratosphere. Here we present an analysis of new v7.0 SAGE II data which shows a smaller upper stratosphere ozone SCS, due to a more realistic ozone-temperature anticorrelation. New simulations from a state-of-art 3-D chemical transport model show a small SCS in the upper stratosphere, which is in agreement with SAGE v7.0 data and the shorter Halogen Occultation Experiment and Microwave Limb Sounder records. However, despite these improvements in the SAGE II data, there are still large uncertainties in current observational and meteorological reanalysis data sets, so accurate quantification of the influence of solar flux variability on the climate system remains an open scientific question.
Sukhodolov T, Rozanov E, Ball WT, et al., 2016, Evaluation of simulated photolysis rates and their response to solar irradiance variability, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 121, Pages: 6066-6084, ISSN: 2169-897X
The state of the stratospheric ozone layer and the temperature structure of the atmosphere are largely controlled by the solar spectral irradiance (SSI) through its influence on heating and photolysis rates. This study focuses on the uncertainties in the photolysis rate response to solar irradiance variability related to the choice of SSI data set and to the performance of the photolysis codes used in global chemistry-climate models. To estimate the impact of SSI uncertainties, we compared several photolysis rates calculated with the radiative transfer model libRadtran, using SSI calculated with two models and observed during the Solar Radiation and Climate Experiment (SORCE) satellite mission. The importance of the calculated differences in the photolysis rate response for ozone and temperature changes has been estimated using 1-D a radiative-convective-photochemical model. We demonstrate that the main photolysis reactions, responsible for the solar signal in the stratosphere, are highly sensitive to the spectral distribution of SSI variations. Accordingly, the ozone changes and related ozone-temperature feedback are shown to depend substantially on the SSI data set being used, which highlights the necessity of obtaining accurate SSI variations. To evaluate the performance of photolysis codes, we compared the results of eight, widely used, photolysis codes against two reference schemes. We show that, in most cases, absolute values of the photolysis rates and their response to applied SSI changes agree within 30%. However, larger errors may appear in specific atmospheric regions because of differences, for instance, in the treatment of Rayleigh scattering, quantum yields, or absorption cross sections.
Ball WT, Haigh JD, Rozanov EV, et al., 2016, High solar cycle spectral variations inconsistent with stratospheric ozone observations, Nature Geoscience, Vol: 9, Pages: 206-209, ISSN: 1752-0894
Haigh JD, 2016, Blue Sky; Mirages, haloes and sundogs; Rainbows; Space Weather; Sunshine; Sunspots and Climate, 30-Second Meteorology: The 50 Most Significant Events and Phenomena, Each Explained in Half a Minute, Editors: Scaife, ISBN: 978-1-7824-0310-4
The discovery of almost two thousand exoplanets has revealed an unexpectedlydiverse planet population. We see gas giants in few-day orbits, whole multi-planet systemswithin the orbit of Mercury, and new populations of planets with masses between that of theEarth and Neptune—all unknown in the Solar System. Observations to date have shown thatour Solar System is certainly not representative of the general population of planets in ourMilky Way. The key science questions that urgently need addressing are therefore: What areexoplanets made of? Why are planets as they are? How do planetary systems work and whatcauses the exceptional diversity observed as compared to the Solar System? The EChO(Exoplanet Characterisation Observatory) space mission was conceived to take up thechallenge to explain this diversity in terms of formation, evolution, internal structure andplanet and atmospheric composition. This requires in-depth spectroscopic knowledge of theatmospheres of a large and well-defined planet sample for which precise physical, chemicaland dynamical information can be obtained. In order to fulfil this ambitious scientificprogram, EChO was designed as a dedicated survey mission for transit and eclipsespectroscopy capable of observing a large, diverse and well-defined planet sample withinits 4-year mission lifetime. The transit and eclipse spectroscopy method, whereby the signalfrom the star and planet are differentiated using knowledge of the planetary ephemerides,allows us to measure atmospheric signals from the planet at levels of at least 10−4 relative tothe star. This can only be achieved in conjunction with a carefully designed stable payloadand satellite platform. It is also necessary to provide broad instantaneous wavelengthcoverage to detect as many molecular species as possible, to probe the thermal structureof the planetary atmospheres and to correct for the contaminating effects of the stellarphotosphere. This requires wavelength coverage of at l
Haigh JD, Matthes K, Hanslmeier A, 2015, The Impact of Solar Variability on Climate., Earth’s climate response to a changing Sun, Editors: Lilensten, Dudok de Wit, Matthes, ISBN: 978-2-7598-1733-7
Ball WT, Krivova NA, Unruh YC, et al., 2014, A New SATIRE-S Spectral Solar Irradiance Reconstruction for Solar Cycles 21-23 and Its Implications for Stratospheric Ozone, JOURNAL OF THE ATMOSPHERIC SCIENCES, Vol: 71, Pages: 4086-4101, ISSN: 0022-4928
Ball WT, Mortlock DJ, Egerton JS, et al., 2014, Assessing the relationship between spectral solar irradiance and stratospheric ozone using Bayesian inference, JOURNAL OF SPACE WEATHER AND SPACE CLIMATE, Vol: 4, ISSN: 2115-7251
Cheung JCH, Haigh JD, Jackson DR, 2014, Impact of EOS MLS ozone data on medium-extended range ensemble weather forecasts, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 119, Pages: 9253-9266, ISSN: 2169-897X
Wen G, Cahalan RF, Haigh JD, et al., 2013, Reconciliation of modeled climate responses to spectral solar forcing, JOURNAL OF GEOPHYSICAL RESEARCH-ATMOSPHERES, Vol: 118, Pages: 6281-6289, ISSN: 2169-897X
Zhong W, Haigh JD, 2013, The greenhouse effect and carbon dioxide, WEATHER, Vol: 68, Pages: 100-105, ISSN: 0043-1656
Dhomse SS, Chipperfield MP, Feng W, et al., 2013, Stratospheric O-3 changes during 2001-2010: the small role of solar flux variations in a chemical transport model, ATMOSPHERIC CHEMISTRY AND PHYSICS, Vol: 13, Pages: 10113-10123, ISSN: 1680-7316
Solanki SK, Krivova NA, Haigh JD, 2013, Solar Irradiance Variability and Climate, ANNUAL REVIEW OF ASTRONOMY AND ASTROPHYSICS, VOL 51, Editors: Faber, VanDishoeck, Publisher: ANNUAL REVIEWS, Pages: 311-351
Orr A, Bracegirdle TJ, Hosking JS, et al., 2013, Strong Dynamical Modulation of the Cooling of the Polar Stratosphere Associated with the Antarctic Ozone Hole, JOURNAL OF CLIMATE, Vol: 26, Pages: 662-668, ISSN: 0894-8755
Orr A, Bracegirdle TJ, Hosking JS, et al., 2012, Possible Dynamical Mechanisms for Southern Hemisphere Climate Change due to the Ozone Hole, JOURNAL OF THE ATMOSPHERIC SCIENCES, Vol: 69, Pages: 2917-2932, ISSN: 0022-4928
Simpson IR, Blackburn M, Haigh JD, 2012, A Mechanism for the Effect of Tropospheric Jet Structure on the Annular Mode-Like Response to Stratospheric Forcing, JOURNAL OF THE ATMOSPHERIC SCIENCES, Vol: 69, Pages: 2152-2170, ISSN: 0022-4928
Roy I, Haigh JD, 2012, Solar Cycle Signals in the Pacific and the Issue of Timings, JOURNAL OF THE ATMOSPHERIC SCIENCES, Vol: 69, Pages: 1446-1451, ISSN: 0022-4928
North GR, Baker DN, Bradley RS, et al., 2012, The Effects of Solar Variability on Earth's Climate: A Workshop Report., Washington DC, Publisher: National Academies Press
Ineson S, Scaife AA, Knight JR, et al., 2011, Solar forcing of winter climate variability in the Northern Hemisphere, NATURE GEOSCIENCE, Vol: 4, Pages: 753-757, ISSN: 1752-0894
Haigh JD, 2011, Solar Influences on Climate, Grantham Institute for Climate Change Briefing Paper No 5, Publisher: Imperial College London
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