Stratospheric Temperature Trends Research Articles

Projected rapid response of stratospheric temperature to stringent climate mitigation

Deep, rapid and sustained reductions in greenhouse gas emissions are required to meet the 2015 Paris Agreement climate target. If the world strengthens efforts toward near-term decarbonisation and undertakes major societal transformation, this will be met with requests from policymakers and the public for evidence that our actions are working and there are demonstrable effects on the climate system. Global surface temperature exhibits large internal variability on interannual to decadal timescales, meaning a reduction in the magnitude of surface warming would not be robustly attributable to climate mitigation for some time. In contrast, global stratospheric temperature trends have much higher signal-to-noise ratios and could offer an early indication of the effects of climate mitigation. Here we examine projected near-term global temperature trends at the surface and in the stratosphere using large ensemble climate models following three future emission scenarios. Under rapid, deep emission cuts following SSP1–1.9, modelled middle and upper stratospheric cooling trends show a detectable weakening within 5 years compared to a scenario approximately representing current climate commitments (SSP2–4.5). Therefore, stratospheric temperature trends could serve as an early indicator to policymakers and the public that climate mitigation is taking effect.

Study on long term troposphere lower stratosphere temperature (TLST) trend in tropical and subtropical northern hemisphere using ground based and COSMIC satellite data

The troposphere, the lowest and closest layer of the atmosphere, is where all meteorological events take place. The tropospheric — lower stratospheric (TLS) temperature trend is determined using linear regression and is essential to comprehending the consequences of climate change in the future. In this article, we explored the long-term temperature variabilities and trends of TLS (1–25 km) temperature and its responses by natural drivers such as El Nino southern oscillation (ENSO), solar flux (SF), quasi-biannual oscillation (QBO), Indian ocean dipole (IOD), and aerosol indexes (AI) using monthly averaged zonal mean COSMIC satellite and ground — based Radiosonde (RS) observations for the period of 2006 – 2020 over tropical station Addis (90 N, 38.80 E) and subtropical station Cairo (30.030 N, 31.230 E). The tropopause is located at the tropical station Addis at 17 km with a temperature of 190–194 K, and for the subtropical station Cairo, it is located at 15 km with a temperature of 201 K, which supports the decrement of tropopause height from the tropics to the subtropics with a slight increase in temperature. The two main oscillations in the TLS region can be seen by using the wavelet analysis technique: the semiannual oscillation (SAO) and the annual oscillation (AO), with the AO being especially strong in the lower troposphere. Furthermore, Morlet wavelet analysis on cold-point tropopause temperature CPTt displays AO and cold point tropopause height CPTh reveals a QBO-like signal. The TLS region has positive peaks at heights of 7, 21, 22, 13, and 4 km for the Addis station, and at 15, 19, 25, 15, and 16 km for the Cairo station in response to natural drivers such as ENSO, SF, QBO, IOD, and aerosol. Lag analyses demonstrate a one-month delay for all natural forcings, except for oceanic indices and SSF, up to three months below the tropopause (below 15 km). There is a noticeable 3 to 4 months lag in every oscillation above the tropopause. A warming trend in the tropospheric region and a cooling trend in the UTLS regions are revealed by MLR trend analysis. In contrast to the subtropical Cairo station, which has the highest warming rate of 0.38 K/decade at 2 km and the maximum cooling rate of −0.2 K/decade at 10 km, the tropical Addis station has the highest cooling rate of −0.38 K/decade at 12 km and the highest warming rate of 0.28 K/decade at 3 km. Our trend findings are consistent with previous research.

Why the lower stratosphere cools when the troposphere warms

Observational data have long suggested that in the tropics, when the troposphere locally warms, the lower stratosphere locally cools. Here, the observed anti-correlation between tropospheric and lower stratospheric temperature is confirmed-the lower stratosphere cools by approximately 2 degrees per degree of warming in the mid-troposphere. This anti-correlation is explained through a recently proposed theory holding that there is a quasi-balanced response of the stratosphere to tropospheric heating [J. Lin, K. Emanuel, Tropospheric thermal forcing of the stratosphere through quasi-balanced dynamics. J. Atmos. Sci. (2024).]. The local-scale anti-correlation between tropospheric and lower stratospheric temperature also holds when considering climate change-where the troposphere has been anomalously warming relative to the zonal mean, the lower stratosphere has been anomalously cooling, and vice versa. This suggests that zonally asymmetries in tropospheric temperature trends will be reflected in that of the lower stratospheric temperature trends. The zonally asymmetric trends are also found to be comparable in magnitude to the mean temperature trends in the lower stratosphere, highlighting the importance of the pattern of warming. The results and proposed theory suggest that in addition to forcing via wave-dissipation, the lower stratosphere can also be subject to direct forcing by the troposphere, through quasi-steady, quasi-balanced dynamics.

Influence of Stratospheric Ozone Changes on Stratospheric Temperature Trends in Recent Decades

Associated with the recovery of stratospheric ozone, stratospheric cooling has decelerated since the late 1990s. This study investigates the contribution of ozone changes to the long-term stratospheric temperature trends in recent decades using satellite observations and model simulations. Observational analysis shows that total column ozone experienced little depletion in the Northern Hemisphere (NH) and weak recovery in the Southern Hemisphere (SH) in the period 1998–2020. It is found that the cease of stratospheric ozone depletion has reduced the stratospheric cooling from 1998 onwards, especially in the summer hemisphere. The correlation analysis indicates that the lower-stratospheric temperature is primarily regulated by ozone changes. The ozone recovery in the SH is associated with the weak warming in the lower stratosphere in the period 1998–2020 in summer. The impact of ozone changes is further isolated in the ozone-only experiments from CMIP6. We find that ozone depletion results in significant cooling in the summer hemisphere in the period 1979–1997, especially in the upper and lower stratosphere, while ozone recovery leads to significant warming in the summer hemisphere in the period 1998–2020 in the upper stratosphere. Our results also suggest that the wave-mean flow interactions associated with stratospheric ozone variations may play an important role in regulating the strength of polar vortex in winter.

Dynamic multiscale spatiotemporal models for multivariate Gaussian data

We propose a novel class of multiscale spatiotemporal models for multivariate Gaussian data. First, we decompose the multivariate data and the underlying latent process with a novel multivariate multiscale decomposition. This decomposition results in multiscale coefficient matrices with elements that are multiscale approximations of spatial directional derivatives. We then assume that the associated latent multiscale coefficient matrices evolve through time with matrix-variate state-space equations. We allow for different speeds of change through time for each latent multiscale coefficient matrix, which induces distinct spatiotemporal dynamics for the mean process in different regions at multiple spatial scales of resolution. This flexible model framework allows for both stationary and nonstationary latent multiscale spatiotemporal processes. Further, we develop a singular matrix-variate forward filter backward sampler for efficient posterior exploration. Importantly for practical purposes, our proposed multiscale spatiotemporal algorithm scales linearly with dataset size and is fully parallelizable. To illustrate the usefulness and flexibility of our dynamic multivariate multiscale framework, we present an application to the spatiotemporal NCEP/NCAR Reanalysis-I dataset on stratospheric temperatures over North America from 1951 to 2016. Our analysis indicates substantial long-term trends in stratospheric temperatures.

The vertical profile of recent tropical temperature trends: Persistent model biases in the context of internal variability

Tropospheric and stratospheric tropical temperature trends in recent decades have been notoriously hard to simulate using climate models, particularly in the upper troposphere. Aside from the warming trend itself, this has broader implications, e.g. atmospheric circulation trends depend on latitudinal temperature gradients. In this study, tropical temperature trends in the CMIP6 models are examined, from 1979 to 2014, and contrasted with trends from the RICH/RAOBCORE radiosondes, and the ERA5/5.1 reanalysis. As in earlier studies, we find considerable warming biases in the CMIP6 modeled trends, and we show that these biases are linked to biases in surface temperature. We also uncover previously undocumented biases in the lower-middle stratosphere: the CMIP6 models appear unable to capture the time evolution of stratospheric cooling, which is non-monotonic owing to the Montreal Protocol. Finally, using models with large ensembles, we show that their standard deviation in tropospheric temperature trends, which is due to internal variability alone, explains ∼ 50% (± 20%) of that from the CMIP6 models.

Seasonal stratospheric ozone trends over 2000–2018 derived from several merged data sets

Abstract. In this work, we analyze the seasonal dependence of ozone trends in the stratosphere using four long-term merged data sets, SAGE-CCI-OMPS, SAGE-OSIRIS-OMPS, GOZCARDS, and SWOOSH, which provide more than 30 years of monthly zonal mean ozone profiles in the stratosphere. We focus here on trends between 2000 and 2018. All data sets show similar results, although some discrepancies are observed. In the upper stratosphere, the trends are positive throughout all seasons and the majority of latitudes. The largest upper-stratospheric ozone trends are observed during local winter (up to 6 % per decade) and equinox (up to 3 % per decade) at mid-latitudes. In the equatorial region, we find a very strong seasonal dependence of ozone trends at all altitudes: the trends vary from positive to negative, with the sign of transition depending on altitude and season. The trends are negative in the upper-stratospheric winter (−1 % per decade to −2 % per decade) and in the lower-stratospheric spring (−2 % per decade to −4 % per decade), but positive (2 % per decade to 3 % per decade) at 30–35 km in spring, while the opposite pattern is observed in summer. The tropical trends below 25 km are negative and maximize during summer (up to −2 % per decade) and spring (up to −3 % per decade). In the lower mid-latitude stratosphere, our analysis points to a hemispheric asymmetry: during local summers and equinoxes, positive trends are observed in the south (+1 % per decade to +2 % per decade), while negative trends are observed in the north (−1 % per decade to −2 % per decade). We compare the seasonal dependence of ozone trends with available analyses of the seasonal dependence of stratospheric temperature trends. We find that ozone and temperature trends show positive correlation in the dynamically controlled lower stratosphere and negative correlation above 30 km, where photochemistry dominates. Seasonal trend analysis gives information beyond that contained in annual mean trends, which can be helpful in order to better understand the role of dynamical variability in short-term trends and future ozone recovery predictions.

Revisiting the Mystery of Recent Stratospheric Temperature Trends

Simulated stratospheric temperatures over the period 1979-2016 in models from the Chemistry-Climate Model Initiative (CCMI) are compared with recently updated and extended satellite observations. The multi-model mean global temperature trends over 1979- 2005 are -0.88 ± 0.23, -0.70 ± 0.16, and -0.50 ± 0.12 K decade-1 for the Stratospheric Sounding Unit (SSU) channels 3 (~40-50 km), 2 (~35-45 km), and 1 (~25-35 km), respectively. These are within the uncertainty bounds of the observed temperature trends from two reprocessed satellite datasets. In the lower stratosphere, the multi-model mean trend in global temperature for the Microwave Sounding Unit channel 4 (~13-22 km) is -0.25 ± 0.12 K decade-1 over 1979-2005, consistent with estimates from three versions of this satellite record. The simulated stratospheric temperature trends in CCMI models over 1979-2005 agree with the previous generation of chemistry-climate models. The models and an extended satellite dataset of SSU with the Advanced Microwave Sounding Unit-A show weaker global stratospheric cooling over 1998-2016 compared to the period of intensive ozone depletion (1979-1997). This is due to the reduction in ozone-induced cooling from the slow-down of ozone trends and the onset of ozone recovery since the late 1990s. In summary, the results show much better consistency between simulated and satellite observed stratospheric temperature trends than was reported by Thompson et al. (2012) for the previous versions of the SSU record and chemistry-climate models. The improved agreement mainly comes from updates to the satellite records; the range of simulated trends is comparable to the previous generation of models.

Enhancing the Data Coverage in the Integrated Global Radiosonde Archive

AbstractThe Integrated Global Radiosonde Archive (IGRA) is a collection of historical and near-real-time radiosonde and pilot balloon observations from around the globe. Consisting of a foundational dataset of individual soundings, a set of sounding-derived parameters, and monthly means, the collection is maintained and distributed by the National Oceanic and Atmospheric Administration’s National Centers for Environmental Information (NCEI). It has been used in a variety of applications, including reanalysis projects, assessments of tropospheric and stratospheric temperature and moisture trends, a wide range of studies of atmospheric processes and structures, and as validation of observations from other observing platforms. In 2016, NCEI released version 2 of the dataset, IGRA 2, which incorporates data from a considerably greater number of data sources, thus increasing the data volume by 30%, extending the data back in time to as early as 1905, and improving the spatial coverage. To create IGRA 2, 40 data sources were converted into a common data format and merged into one coherent dataset using a newly designed suite of algorithms. Then, an overhauled version of the IGRA 1 quality-assurance system was applied to the integrated data. Last, monthly means and sounding-by-sounding moisture and stability parameters were derived from the new dataset. All of these components are updated on a regular basis and made available for download free of charge on the NCEI website.

Long-term trends in stratospheric ozone, temperature, and water vapor over the Indian region

Abstract. We have investigated the long-term trends in and variabilities of stratospheric ozone, water vapor and temperature over the Indian monsoon region using the long-term data constructed from multi-satellite (Upper Atmosphere Research Satellite (UARS MLS and HALOE, 1993–2005), Aura Microwave Limb Sounder (MLS, 2004–2015), Sounding of the Atmosphere using Broadband Emission Radiometry (SABER, 2002–2015) on board TIMED (Thermosphere Ionosphere Mesosphere Energetics Dynamics)) observations covering the period 1993–2015. We have selected two locations, namely, Trivandrum (8.4∘ N, 76.9∘ E) and New Delhi (28∘ N, 77∘ E), covering northern and southern parts of the Indian region. We also used observations from another station, Gadanki (13.5∘ N, 79.2∘ E), for comparison. A decreasing trend in ozone associated with NOx chemistry in the tropical middle stratosphere is found, and the trend turned to positive in the upper stratosphere. Temperature shows a cooling trend in the stratosphere, with a maximum around 37 km over Trivandrum (−1.71 ± 0.49 K decade−1) and New Delhi (−1.15 ± 0.55 K decade−1). The observed cooling trend in the stratosphere over Trivandrum and New Delhi is consistent with Gadanki lidar observations during 1998–2011. The water vapor shows a decreasing trend in the lower stratosphere and an increasing trend in the middle and upper stratosphere. A good correlation between N2O and O3 is found in the middle stratosphere (∼ 10 hPa) and poor correlation in the lower stratosphere. There is not much regional difference in the water vapor and temperature trends. However, upper stratospheric ozone trends over Trivandrum and New Delhi are different. The trend analysis carried out by varying the initial year has shown significant changes in the estimated trend. Keywords. Atmospheric composition and structure (middle atmosphere – composition and chemistry; troposphere – composition and chemistry) – meteorology and atmospheric dynamics (climatology)

Troposphere‐Stratosphere Temperature Trends Derived From Satellite Data Compared With Ensemble Simulations From WACCM

AbstractDecadal‐scale trends in tropospheric and stratospheric temperatures derived from satellite measurements over 1979–2014 are compared with ensemble simulations from the Whole Atmosphere Community Climate Model (WACCM). The model is forced with observed sea surface temperatures, changes in greenhouse gases, and ozone‐depleting substances, plus solar and volcanic effects, and results from five WACCM realizations (with slightly different initial conditions) are analyzed. We focus on the vertical structure of tropospheric warming and stratospheric cooling increasing with height, the latitudinal and seasonal dependence of trends, and on the temporal evolution of stratospheric temperatures in response to stratospheric ozone depletion and partial recovery. The model captures the observed trend structure in most respects, and the ensemble of simulations provides quantitative estimates of the impact of internal variability on trend estimates. In regions of low variability (e.g., over low latitudes) the ensemble mean trends agree with the observations, while in regions of high variability (e.g., the polar stratosphere) the observations mostly fall within the range of realizations. Temperature response to evolving stratospheric ozone is evaluated by computing separate trends over 1979–1997 (ozone depletion) and 1998–2014 (partial recovery). Robust changes in temperature trends between these periods occur in the global upper stratosphere and in the Antarctic spring lower stratosphere, with consistent behavior between model and observations. Observed lower stratospheric temperatures in the Antarctic show statistically significant warming after 1998, reflecting recently reported healing of the ozone hole.

The Stratospheric Changes Inferred from 10 Years of AIRS and AMSU-A Radiances

AbstractGlobal-mean radiances observed by the Atmospheric Infrared Sounder (AIRS) and the Advanced Microwave Sounding Unit A (AMSU-A) are analyzed from 2003 to 2012. The focus of this study is on channels sensitive to emission and absorption in the stratosphere. Optimal fingerprinting is used to obtain estimates of changes of stratospheric temperature in five vertical layers due to external forcing in the presence of natural variability. Natural variability is estimated using synthetic radiances based on the 500-yr GFDL CM3 and 240-yr HadGEM2-CC control runs. The results show a cooling rate of 0.65 ± 0.11 (2σ) K decade−1 in the upper stratosphere above 6 hPa, approximately 0.46 ± 0.24 K decade−1 in two midstratospheric layers between 6 and 30 hPa, and 0.39 ± 0.32 K decade−1 in the lower stratosphere (30–60 hPa). The cooling rate in the lowest part of the stratosphere (60–100 hPa) is −0.014 ± 0.22 K decade−1, which is smallest among all five layers and statistically insignificant. The synergistic use of well-calibrated passive infrared and microwave radiances permits disambiguation of trends of carbon dioxide and stratospheric temperature, increases vertical resolution of detected stratospheric temperature trends, and effectively reduces uncertainties of estimated temperature trends.

Revisiting Southern Hemisphere polar stratospheric temperature trends in WACCM: The role of dynamical forcing

AbstractThe latest version of the Whole Atmosphere Community Climate Model (WACCM), which includes a new chemistry scheme and an updated parameterization of orographic gravity waves, produces temperature trends in the Antarctic lower stratosphere in excellent agreement with radiosonde observations for 1969–1998 as regards magnitude, location, timing, and persistence. The maximum trend, reached in November at 100 hPa, is −4.4 ± 2.8 K decade−1, which is a third smaller than the largest trend in the previous version of WACCM. Comparison with a simulation without the updated orographic gravity wave parameterization, together with analysis of the model's thermodynamic budget, reveals that the reduced trend is due to the effects of a stronger Brewer‐Dobson circulation in the new simulations, which warms the polar cap. The effects are both direct (a trend in adiabatic warming in late spring) and indirect (a smaller trend in ozone, hence a smaller reduction in shortwave heating, due to the warmer environment).

Regional and seasonal stratospheric temperature trends in the last decade (2002–2014) from AMSU observations

AbstractStratospheric temperature trends for the period 2002–2014 have been estimated using NOAA's Integrated Microwave Inter‐calibration Approach (IMICA) version of advanced microwave sounding unit (AMSU) on AQUA satellite. In this period the stratosphere continued cooling over most of the globe with a rate ranging from −0.4 ± 0.3 to −0.5 ± 0.4 K/decade above 25 km. Considering specific latitude bands, trends are highly variable with height. In the tropical region, trends vary from −0.5 ± 0.3 K/decade for channel 12 (∼30 km) to −0.7 ± 0.3 K/decade for higher channels and present small seasonal variability in the intensity of cooling. In the polar regions and in the midlatitudes, trends for all channels are negative but not significant; uncertainties are large due to the high dynamical variability particularly in high latitudes. There is also large seasonal variability, with southern midlatitudes seasonal trends significant during summer (December, January, February) and autumn (March, April, May) above ∼25 km, with values ranging from −1.0 ± 0.5 to −0.6 ± 0.5 K/decade. Regional trends estimated with AMSU and long‐term lidar measurements (over two decades) confirm stratospheric cooling in the northern midlatitudes and tropical regions. The effect of the length of the short series on trends was found to be small outside polar regions. It was found to be large in polar regions with about 1 K changes in trend depending on start dates of the time series.

Radiative and Dynamical Influences on Polar Stratospheric Temperature Trends

Abstract Radiative and dynamical heating rates control stratospheric temperatures. In this study, radiative temperature trends due to ozone depletion and increasing well-mixed greenhouse gases from 1980 to 2000 in the polar stratosphere are directly evaluated, and the dynamical contributions to temperature trends are estimated as the residual between the observed and radiative trends. The radiative trends are obtained from a seasonally evolving fixed dynamical heating calculation with the Parallel Offline Radiative Transfer model using four different ozone datasets, which provide estimates of observed ozone changes. In the spring and summer seasons, ozone depletion leads to radiative cooling in the lower stratosphere in the Arctic and Antarctic. In Arctic summer there is weak wave driving, and the radiative cooling due to ozone depletion is the dominant driver of observed trends. In late winter and early spring, dynamics dominate the changes in Arctic temperatures. In austral spring and summer in the Antarctic, strong dynamical warming throughout the mid- to lower stratosphere acts to weaken the strong radiative cooling associated with the Antarctic ozone hole and is indicative of a strengthening of the Brewer–Dobson circulation. This dynamical warming is a significant term in the thermal budget over much of the Antarctic summer stratosphere, including in regions where strong radiative cooling due to ozone depletion can still lead to net cooling despite dynamical terms. Quantifying the contributions of changes in radiation and dynamics to stratospheric temperature trends is important for understanding how anthropogenic forcings have affected the historical trends and necessary for projecting the future.

Stratospheric Temperature Trends over 1979–2015 Derived from Combined SSU, MLS, and SABER Satellite Observations

Abstract Temperature trends in the middle and upper stratosphere are evaluated using measurements from the Stratospheric Sounding Unit (SSU), combined with data from the Aura Microwave Limb Sounder (MLS) and Sounding of the Atmosphere Using Broadband Emission Radiometry (SABER) instruments. Data from MLS and SABER are vertically integrated to approximate the SSU weighting functions and combined with SSU to provide a data record spanning 1979–2015. Vertical integrals are calculated using empirically derived Gaussian weighting functions, which provide improved agreement with high-latitude SSU measurements compared to previously derived weighting functions. These merged SSU data are used to evaluate decadal-scale trends, solar cycle variations, and volcanic effects from the lower to the upper stratosphere. Episodic warming is observed following the volcanic eruptions of El Chichón (1982) and Mt. Pinatubo (1991), focused in the tropics in the lower stratosphere and in high latitudes in the middle and upper stratosphere. Solar cycle variations are centered in the tropics, increasing in amplitude from the lower to the upper stratosphere. Linear trends over 1979–2015 show that cooling increases with altitude from the lower stratosphere (from ~−0.1 to −0.2 K decade−1) to the middle and upper stratosphere (from ~−0.5 to −0.6 K decade−1). Cooling in the middle and upper stratosphere is relatively uniform in latitudes north of about 30°S, but trends decrease to near zero over the Antarctic. Mid- and upper-stratospheric temperatures show larger cooling over the first half of the data record (1979–97) compared to the second half (1998–2015), reflecting differences in upper-stratospheric ozone trends between these periods.

Long term trends in stratospheric temperature using NCEP/NCAR data

The stratospheric temperature trend plays an important role in distinguishing between the climate systems responses to natural and human induced changes. A linear trend of monthly mean temperature from the NCEP/NCAR reanalysis dataset for both Hemispheres with 2.5° step in latitude and longitude for the period 1979–2011, were calculated on this paper. Four different stratospheric heights: 10hPa, 30hPa, 50hPa, and 70hPa were analyzed. The observed trend pattern changes with height as expected. The area of negative trends increases when we go up in the stratosphere. Lower and middle stratosphere shows positive trends, in a section of the latitudinal band between 50°S and 60°S. As we go down the stratosphere these positive trends are smoother. At 10hPa all trends are negative. In Southern Hemisphere at 30hPa significant negative trends at low middle latitudes were observed. These results were compared with others, obtained by models and observations.

The contribution of ozone to future stratospheric temperature trends

AbstractThe projected recovery of ozone from the effects of ozone depleting substances this century will modulate the stratospheric cooling due to CO2, thereby affecting the detection and attribution of stratospheric temperature trends. Here the impact of future ozone changes on stratospheric temperatures is quantified for three representative concentration pathways (RCPs) using simulations from the Fifth Coupled Model Intercomparison Project (CMIP5). For models with interactive chemistry, ozone trends offset ~50% of the global annual mean upper stratospheric cooling due to CO2 for RCP4.5 and 20% for RCP8.5 between 2006–2015 and 2090–2099. For RCP2.6, ozone trends cause a net warming of the upper and lower stratosphere. The misspecification of ozone trends for RCP2.6/RCP4.5 in models that used the International Global Atmospheric Chemistry (IGAC)/Stratosphere‐troposphere Processes and their Role in Climate (SPARC) Ozone Database causes anomalous warming (cooling) of the upper (lower) stratosphere compared to chemistry‐climate models. The dependence of ozone chemistry on greenhouse gas concentrations should therefore be better represented in CMIP6.

Use of SSU/MSU Satellite Observations to Validate Upper Atmospheric Temperature Trends in CMIP5 Simulations

The tropospheric and stratospheric temperature trends and uncertainties in the fifth Coupled Model Intercomparison Project (CMIP5) model simulations in the period of 1979–2005 have been compared with satellite observations. The satellite data include those from the Stratospheric Sounding Units (SSU), Microwave Sounding Units (MSU), and the Advanced Microwave Sounding Unit-A (AMSU). The results show that the CMIP5 model simulations reproduced the common stratospheric cooling (−0.46–−0.95 K/decade) and tropospheric warming (0.05–0.19 K/decade) features although a significant discrepancy was found among the individual models being selected. The changes of global mean temperature in CMIP5 simulations are highly consistent with the SSU measurements in the stratosphere, and the temporal correlation coefficients between observation and model simulations vary from 0.6–0.99 at the 99% confidence level. At the same time, the spread of temperature mean in CMIP5 simulations increased from stratosphere to troposphere. Multiple linear regression analysis indicates that the temperature variability in the stratosphere is dominated by radioactive gases, volcanic events and solar forcing. Generally, the high-top models show better agreement with observations than the low-top model, especially in the lower stratosphere. The CMIP5 simulations underestimated the stratospheric cooling in the tropics and overestimated the cooling over the Antarctic compared to the satellite observations. The largest spread of temperature trends in CMIP5 simulations is seen in both the Arctic and Antarctic areas, especially in the stratospheric Antarctic.

A review of Stratospheric Sounding Unit radiance observations for climate trends and reanalyses

Stratospheric Sounding Units (SSU) on the NOAA polar‐orbiting satellites measured infrared radiances in the 15 μm CO2 band between late 1978 and mid‐2006. From these radiances a time series of layer‐mean stratospheric temperatures has been derived by several groups. Discrepancies in these temperature analyses have been highlighted recently and efforts are now underway to resolve the differences between them. This article is the Met Office response summarising the issues to be resolved in creating a climate data record from the different SSUs, including corrections for radiometric, spectroscopic and tidal differences. Calibration issues identified include the SSU space‐view anomaly and radiometric anomalies in the NOAA‐9 observations. The spectroscopic correction required for changing pressures in the pressure modulator cells is also outlined. The most important correction for the time series is for the solar diurnal and semi‐diurnal tides as the satellite overpass local times change. Comparisons with other stratospheric temperature trend analyses are made and the reasons for the differences discussed. The time series presented here show sustained drops in stratospheric temperatures at all levels after the El Chichon and Pinatubo eruptions but only small trends to lower temperatures between eruptions.