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

Global-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 (2 σ) 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.

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Robustness of Tropospheric Temperature Trends from MSU Channels 2 and 4

Journal of Climate ◽

10.1175/jcli3866.1 ◽

2006 ◽

Vol 19 (17) ◽

pp. 4234-4242 ◽

Cited By ~ 22

Author(s):

Celeste M. Johanson ◽

Qiang Fu

Keyword(s):

Training Dataset ◽

Retrieval Algorithm ◽

Tropospheric Temperature ◽

Temperature Trends ◽

Combining Data ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

The Mean ◽

Stratospheric Cooling ◽

Global Mean

Abstract Tropospheric temperature trends based on Microwave Sounding Unit (MSU) channel 2 data are susceptible to contamination from strong stratospheric cooling. Recently, Fu et al. devised a method of removing the stratospheric contamination by linearly combining data from MSU channels 2 and 4. In this study the sensitivity of the weights of the two channels in the retrieval algorithm for the tropospheric temperatures to the choice of period of record used in the analysis and to the choice of training dataset is examined. The weights derived using monthly temperature anomalies are within about 10% of those obtained by Fu et al. irrespective of the choice of analysis period or training dataset. The trend errors in the retrieved global-mean tropospheric temperatures tested using two independent radiosonde datasets are less than about 0.01 K decade−1 for all time periods of 25 yr or longer with different starting and ending years during 1958–2004. It is found that the retrievals are more robust if they are interpreted in terms of the layer-mean temperature for the entire troposphere, rather than the mean of the 850–300-hPa layer. Because large spurious jumps remain in the reanalyses, especially prior to 1979, one should be cautious when using them as training datasets and in testing the trend errors.

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A method for merging nadir-sounding climate records, with an application to the global-mean stratospheric temperature data sets from SSU and AMSU

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-9271-2015 ◽

2015 ◽

Vol 15 (16) ◽

pp. 9271-9284 ◽

Cited By ~ 13

Author(s):

C. McLandress ◽

T. G. Shepherd ◽

A. I. Jonsson ◽

T. von Clarmann ◽

B. Funke

Keyword(s):

Michelson Interferometer ◽

Data Sets ◽

Climate Data ◽

Data Set ◽

Linear Temperature ◽

Temperature Changes ◽

Stratospheric Temperature ◽

Temperature Trends ◽

Microwave Sounding ◽

Global Mean

Abstract. A method is proposed for merging different nadir-sounding climate data records using measurements from high-resolution limb sounders to provide a transfer function between the different nadir measurements. The two nadir-sounding records need not be overlapping so long as the limb-sounding record bridges between them. The method is applied to global-mean stratospheric temperatures from the NOAA Climate Data Records based on the Stratospheric Sounding Unit (SSU) and the Advanced Microwave Sounding Unit-A (AMSU), extending the SSU record forward in time to yield a continuous data set from 1979 to present, and providing a simple framework for extending the SSU record into the future using AMSU. SSU and AMSU are bridged using temperature measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), which is of high enough vertical resolution to accurately represent the weighting functions of both SSU and AMSU. For this application, a purely statistical approach is not viable since the different nadir channels are not sufficiently linearly independent, statistically speaking. The near-global-mean linear temperature trends for extended SSU for 1980–2012 are −0.63 ± 0.13, −0.71 ± 0.15 and −0.80 ± 0.17 K decade−1 (95 % confidence) for channels 1, 2 and 3, respectively. The extended SSU temperature changes are in good agreement with those from the Microwave Limb Sounder (MLS) on the Aura satellite, with both exhibiting a cooling trend of ~ 0.6 ± 0.3 K decade−1 in the upper stratosphere from 2004 to 2012. The extended SSU record is found to be in agreement with high-top coupled atmosphere–ocean models over the 1980–2012 period, including the continued cooling over the first decade of the 21st century.

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How Robust Are Trends in the Brewer–Dobson Circulation Derived from Observed Stratospheric Temperatures?

Journal of Climate ◽

10.1175/jcli-d-14-00295.1 ◽

2015 ◽

Vol 28 (8) ◽

pp. 3024-3040 ◽

Cited By ~ 7

Author(s):

Albert Ossó ◽

Yolanda Sola ◽

Karen Rosenlof ◽

Birgit Hassler ◽

Joan Bech ◽

...

Keyword(s):

Radiative Forcing ◽

First Century ◽

Global Circulation ◽

Global Circulation Models ◽

Global Mean Temperature ◽

Stratospheric Temperature ◽

Spatially Inhomogeneous ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

Global Mean

Abstract Most global circulation models and climate–chemistry models forced with increasing greenhouse gases predict a strengthening of the Brewer–Dobson circulation (BDC) in the twenty-first century, and some of them claim that such strengthening has already begun at the end of the twentieth century. However, observational evidence for such a trend remains inconclusive. The goal of this paper is to examine the evidence for observed trends in the stratospheric overturning circulation using a suite of currently available observational stratospheric temperature data. Trends are examined as “departures” from the global mean temperature, since such trends reflect the effects of dynamics and spatially inhomogeneous radiative forcing and are to first order independent of the direct radiative effects of increasing well-mixed greenhouse gas concentrations. The primary conclusion of the study is that temperature observations do not reveal statistically significant trends in the Brewer–Dobson circulation over the period from 1979 to the present, as covered by Microwave Sounding Unit and Stratospheric Sounding Unit temperatures. The estimated trends in the BDC are weak in all datasets and not statistically significant at the 95% confidence level. In many cases, different data products yield very different results, particularly when the trends are stratified by season. Implications for the interpretation of recent stratospheric climate change are discussed. The results illustrate the essential need to better constrain the accuracy of future stratospheric temperature datasets.

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A method for merging nadir-sounding climate records, with an application to the global-mean stratospheric temperature data sets from SSU and AMSU

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-10085-2015 ◽

2015 ◽

Vol 15 (7) ◽

pp. 10085-10122 ◽

Cited By ~ 2

Author(s):

C. McLandress ◽

T. G. Shepherd ◽

A. I. Jonsson ◽

T. von Clarmann ◽

B. Funke

Keyword(s):

Climate Model ◽

Michelson Interferometer ◽

Data Sets ◽

Climate Data ◽

Data Set ◽

Stratospheric Temperature ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

Climate Model Simulations ◽

Global Mean

Abstract. A method is proposed for merging different nadir-sounding climate data records using measurements from high resolution limb sounders to provide a transfer function between the different nadir measurements. The nadir-sounding records need not be overlapping so long as the limb-sounding record bridges between them. The method is applied to global mean stratospheric temperatures from the NOAA Climate Data Records based on the Stratospheric Sounding Unit (SSU) and the Advanced Microwave Sounding Unit-A (AMSU), extending the SSU record forward in time to yield a continuous data set from 1979 to present. SSU and AMSU are bridged using temperature measurements from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), which is of high enough vertical resolution to accurately represent the weighting functions of both SSU and AMSU. For this application, a purely statistical approach is not viable since the different nadir channels are not sufficiently linearly independent, statistically speaking. The extended SSU global-mean data set is in good agreement with temperatures from the Microwave Limb Sounder (MLS) on the Aura satellite, with both exhibiting a cooling trend of ~ 0.6 ± 0.3 K decade−1 in the upper stratosphere from 2004–2012. The extended SSU data set also compares well with chemistry-climate model simulations over its entire record, including the contrast between the weak cooling seen over 1995–2004 compared with the large cooling seen in the period 1986–1995 of strong ozone depletion.

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Biases in Stratospheric and Tropospheric Temperature Trends Derived from Historical Radiosonde Data

Journal of Climate ◽

10.1175/jcli3717.1 ◽

2006 ◽

Vol 19 (10) ◽

pp. 2094-2104 ◽

Cited By ~ 94

Author(s):

William J. Randel ◽

Fei Wu

Keyword(s):

Lower Stratosphere ◽

Radiosonde Data ◽

Tropospheric Temperature ◽

Satellite Measurements ◽

Upper Troposphere ◽

Step Functions ◽

Temperature Trends ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

The Tropics

Abstract Temperature trends derived from historical radiosonde data often show substantial differences compared to satellite measurements. These differences are especially large for stratospheric levels, and for data in the Tropics, where results are based on relatively few stations. Detailed comparisons of one radiosonde dataset with collocated satellite measurements from the Microwave Sounding Unit reveal time series differences that occur as step functions or jumps at many stations. These jumps occur at different times for different stations, suggesting that the differences are primarily related to problems in the radiosonde data, rather than in the satellite record. As a result of these jumps, the radiosondes exhibit systematic cooling biases relative to the satellites. A large number of the radiosonde stations in the Tropics are influenced by these biases, suggesting that cooling in the tropical lower stratosphere is substantially overestimated in these radiosonde data. Comparison of trends from stations with larger and smaller biases suggests the cooling bias extends into the tropical upper troposphere. Significant biases are observed in both daytime and nighttime radiosonde measurements.

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On the seasonal dependence of tropical lower-stratospheric temperature trends

Atmospheric Chemistry and Physics ◽

10.5194/acp-10-2643-2010 ◽

2010 ◽

Vol 10 (6) ◽

pp. 2643-2653 ◽

Cited By ~ 44

Author(s):

Q. Fu ◽

S. Solomon ◽

P. Lin

Keyword(s):

Climate Model ◽

The Novel ◽

Marked Contrast ◽

Wave Forcing ◽

Stratospheric Temperature ◽

Temperature Trends ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

Climate Model Simulations ◽

Seasonal Dependence

Abstract. This study examines the seasonality of tropical lower-stratospheric temperature trends using the Microwave Sounding Unit lower-stratospheric channel (T4) for 1980–2008. We present evidence that this seasonality is largely a response to changes in the Brewer-Dobson circulation (BDC) driven by extratropical wave forcing. We show how the tropical T4 trend can be used as an indicator of changes in the BDC, and find that the BDC is strengthening for 1980–2008 in June–November related to the Southern Hemisphere (SH) and in December–February to the Northern Hemisphere (NH). In marked contrast, we find that the BDC is weakening in March–May, apparently because of a weakening of its northern cell. The novel observational evidence on the seasonal dependence of the BDC trends presented in this study has important implications for the understanding of climate change in the stratosphere as well as testing climate model simulations.

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Stratospheric Influences on MSU-Derived Tropospheric Temperature Trends: A Direct Error Analysis

Journal of Climate ◽

10.1175/jcli-3267.1 ◽

2004 ◽

Vol 17 (24) ◽

pp. 4636-4640 ◽

Cited By ~ 29

Author(s):

Qiang Fu ◽

Celeste M. Johanson

Keyword(s):

Error Analysis ◽

Tropospheric Temperature ◽

Retrieval Method ◽

The Past ◽

Stratospheric Temperature ◽

Retrieval Technique ◽

Temperature Trends ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

Angular Scanning

Abstract Retrievals of tropospheric temperature trends from data of the Microwave Sounding Unit (MSU) are subject to biases related to the strong cooling of the stratosphere during the past few decades. The magnitude of this stratospheric contamination in various retrievals is estimated using stratospheric temperature trend profiles based on observations. It is found that from 1979 to 2001 the stratospheric contribution to the trend of MSU channel-2 brightness temperature is about −0.08 K decade−1, which is consistent with the findings of Fu et al. In the retrieval method developed by Fu et al. based on a linear combination of MSU channels 2 and 4, the stratospheric influence is largely removed, leaving a residual influence of less than ±0.01 K decade−1. This method is also found to be more accurate than the angular scanning retrieval technique of Spencer and Christy to remove the stratospheric contamination.

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On the seasonal dependence of tropical lower-stratospheric temperature trends

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-9-21819-2009 ◽

2009 ◽

Vol 9 (5) ◽

pp. 21819-21846 ◽

Cited By ~ 2

Author(s):

Q. Fu ◽

S. Solomon ◽

P. Lin

Keyword(s):

Climate Model ◽

The Novel ◽

Marked Contrast ◽

Wave Forcing ◽

Stratospheric Temperature ◽

Temperature Trends ◽

Microwave Sounding Unit ◽

Microwave Sounding ◽

Climate Model Simulations ◽

Seasonal Dependence

Abstract. This study examines the seasonality of tropical lower-stratospheric temperature trends using the Microwave Sounding Unit lower-stratospheric channel (T4) for 1979–2007. We present evidence that this seasonality is a response to changes in the Brewer–Dobson circulation (BDC) driven by extratropical wave forcing. We show how the tropical T4 trend can be used as an indicator of the change in the BDC, and find that the BDC is strengthening for 1979–2007 in June–November related to the Southern Hemisphere (SH) and in December–February to the Northern Hemisphere (NH). In marked contrast, we find that the BDC is weakening in March–May, apparently because of a weakening of its northern cell. The novel observational evidence on the seasonal dependence of the BDC trends presented in this study has important implications for the understanding of climate change in the stratosphere as well as testing climate model simulations.

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Construction of the RSS V3.2 Lower-Tropospheric Temperature Dataset from the MSU and AMSU Microwave Sounders

Journal of Atmospheric and Oceanic Technology ◽

10.1175/2009jtecha1237.1 ◽

2009 ◽

Vol 26 (8) ◽

pp. 1493-1509 ◽

Cited By ~ 52

Author(s):

Carl A. Mears ◽

Frank J. Wentz

Keyword(s):

Lower Stratosphere ◽

Weighting Function ◽

Lower Troposphere ◽

Weighted Average ◽

Atmospheric Temperature ◽

Tropospheric Temperature ◽

Satellite Measurements ◽

Microwave Sounding Unit ◽

Different Types ◽

Microwave Sounding

Abstract Measurements made by microwave sounding instruments provide a multidecadal record of atmospheric temperature in several thick atmospheric layers. Satellite measurements began in late 1978 with the launch of the first Microwave Sounding Unit (MSU) and have continued to the present via the use of measurements from the follow-on series of instruments, the Advanced Microwave Sounding Unit (AMSU). The weighting function for MSU channel 2 is centered in the middle troposphere but contains significant weight in the lower stratosphere. To obtain an estimate of tropospheric temperature change that is free from stratospheric effects, a weighted average of MSU channel 2 measurements made at different local zenith angles is used to extrapolate the measurements toward the surface, which results in a measurement of changes in the lower troposphere. In this paper, a description is provided of methods that were used to extend the MSU method to the newer AMSU channel 5 measurements and to intercalibrate the results from the different types of satellites. Then, satellite measurements are compared to results from homogenized radiosonde datasets. The results are found to be in excellent agreement with the radiosonde results in the northern extratropics, where the majority of the radiosonde stations are located.

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Temperature decadal trends, and their relation to diurnal variations in the lower thermosphere, stratosphere, and mesosphere, based on measurements from SABER on TIMED

Annales Geophysicae ◽

10.5194/angeo-39-327-2021 ◽

2021 ◽

Vol 39 (2) ◽

pp. 327-339

Author(s):

Frank T. Huang ◽

Hans G. Mayr

Keyword(s):

Local Time ◽

Lower Thermosphere ◽

3D Models ◽

Diurnal Variations ◽

Local Times ◽

Temperature Trends ◽

Microwave Sounding Unit ◽

Lidar Measurements ◽

Microwave Sounding ◽

Thermal Tides

Abstract. We have derived the behavior of decadal temperature trends over the 24 h of local time, based on zonal averages of SABER data, for the years 2012 to 2014, from 20 to 100 km, within 48∘ of the Equator. Similar results have not been available previously. We find that the temperature trends, based on zonal mean measurements at a fixed local time, can be different from those based on measurements made at a different fixed local time. The trends can vary significantly in local time, even from hour to hour. This agrees with some findings based on nighttime lidar measurements. This knowledge is relevant because the large majority of temperature measurements, especially in the stratosphere, are made by instruments on sun-synchronous operational satellites which measure at only one or two fixed local times, for the duration of their missions. In these cases, the zonal mean trends derived from various satellite data are tied to the specific local times at which each instrument samples the data, and the trends are then also biased by the local time. Consequently, care is needed in comparing trends based on various measurements with each other, unless the data are all measured at the same local time. Similar caution is needed when comparing with models, since the zonal means from 3D models reflect averages over both longitude and the 24 h of local time. Consideration is also needed in merging data from various sources to produce generic, continuous, longer-term records. Diurnal variations of temperature themselves, in the form of thermal tides, are well known and are due to absorption of solar radiation. We find that at least part of the reason that temperature trends are different for different local times is that the amplitudes and phases of the tides themselves follow trends over the same time span of the data. Many of the past efforts have focused on the temperature values with local time when merging data from various sources and on the effect of unintended satellite orbital drifts, which result in drifting local times at which the temperatures are measured. However, the effect of local time on trends has not been well researched. We also derive estimates of trends by simulating the drift of local time due to drifting orbits. Our comparisons with results found by others (Advanced Microwave Sounding Unit, AMSU; lidar) are favorable and informative. They may explain, at least in part, the bridge between results based on daytime AMSU data and nighttime lidar measurements. However, these examples do not form a pattern, and more comparisons and study are needed.

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