scholarly journals Changes in Stratospheric Temperatures and Their Implications for Changes in the Brewer–Dobson Circulation, 1979–2005

2012 ◽  
Vol 25 (5) ◽  
pp. 1759-1772 ◽  
Author(s):  
Paul J. Young ◽  
Karen H. Rosenlof ◽  
Susan Solomon ◽  
Steven C. Sherwood ◽  
Qiang Fu ◽  
...  
Keyword(s):  
Interannual Variability ◽  
Southern Hemisphere ◽  
Seasonal Cycle ◽  
Lower Stratosphere ◽  
Decadal Variability ◽  
Microwave Sounding Unit ◽  
Microwave Sounding ◽  
Apparent Shift ◽  
The Tropics ◽  
Linear Trends

Seasonally and vertically resolved changes in the strength of the Brewer–Dobson circulation (BDC) were inferred using temperatures measured by the Microwave Sounding Unit (MSU), Stratospheric Sounding Unit (SSU), and radiosondes. Linear trends in an empirically derived “BDC index” (extratropical minus tropical temperatures), over 1979–2005, were found to be consistent with a significant strengthening of the Northern Hemisphere (NH) branch of the BDC during December throughout the depth of the stratosphere. Trends in the same index suggest a significant strengthening of the Southern Hemisphere branch of the BDC during August through to the midstratosphere, as well as a significant weakening during March in the NH lower stratosphere. Such trends, however, are only significant if it is assumed that interannual variability due to the BDC can be removed by regression of the tropics against the extratropics and vice versa (i.e., exploiting the out-of-phase nature of tropical and extratropical temperatures as demonstrated by previous studies of temperature and the BDC). The possibility that the apparent lower-stratosphere BDC December strengthening and March weakening could point to a change in the seasonal cycle of the circulation is also explored. The differences between a 1979–91 average and 1995–2005 average tropical temperature seasonal cycle in lower-stratospheric MSU data show an apparent shift in the minimum from February to January, consistent with a change in the timing of the maximum wave driving. Additionally, the importance of decadal variability in shaping the overall trends is highlighted, in particular for the suggested March BDC weakening, which may now be strengthening from a minimum in the 1990s.

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

2006 ◽  
Vol 19 (10) ◽  
pp. 2094-2104 ◽  
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.

scholarly journals Interannual variability of precipitable water

1996 ◽  
Vol 14 (4) ◽  
pp. 464-467 ◽  
Author(s):  
R. P. Kane
Keyword(s):  
Interannual Variability ◽  
Southern Hemisphere ◽  
Northern Hemisphere ◽  
Precipitable Water ◽  
Radiosonde Data ◽  
High Latitudes ◽  
Zonal Winds ◽  
Low Latitudes ◽  
Linear Trends

Abstract. The 12-month running means of the surface-to-500 mb precipitable water obtained from analysis of radiosonde data at seven selected locations showed three types of variability viz: (1) quasi-biennial oscillations; these were different in nature at different latitudes and also different from the QBO of the stratospheric tropical zonal winds; (2) decadal effects; these were prominent at middle and high latitudes and (3) linear trends; these were prominent at low latitudes, up trends in the Northern Hemisphere and downtrends in the Southern Hemisphere.

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

2009 ◽  
Vol 26 (8) ◽  
pp. 1493-1509 ◽  
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.

scholarly journals Variability in the speed of the Brewer–Dobson circulation as observed by Aura/MLS

2013 ◽  
Vol 13 (9) ◽  
pp. 4563-4575 ◽  
Author(s):  
T. Flury ◽  
D. L. Wu ◽  
W. G. Read
Keyword(s):  
Time Series ◽  
Interannual Variability ◽  
Lower Stratosphere ◽  
Meridional Circulation ◽  
Time Lag ◽  
Quasi Biennial Oscillation ◽  
One Year ◽  
The Tropics ◽  
Biennial Oscillation ◽  
Stratospheric Water Vapour

Abstract. We use Aura/MLS stratospheric water vapour (H2O) measurements as tracer for dynamics and infer interannual variations in the speed of the Brewer–Dobson circulation (BDC) from 2004 to 2011. We correlate one-year time series of H2O in the lower stratosphere at two subsequent pressure levels (68 hPa, ~18.8 km and 56 hPa, ~19.9 km at the Equator) and determine the time lag for best correlation. The same calculation is made on the horizontal on the 100 hPa (~16.6 km) level by correlating the H2O time series at the Equator with the ones at 40° N and 40° S. From these lag coefficients we derive the vertical and horizontal speeds of the BDC in the tropics and extra-tropics, respectively. We observe a clear interannual variability of the vertical and horizontal branch. The variability reflects signatures of the Quasi Biennial Oscillation (QBO). Our measurements confirm the QBO meridional circulation anomalies and show that the speed variations in the two branches of the BDC are out of phase and fairly well anti-correlated. Maximum ascent rates are found during the QBO easterly phase. We also find that transport of H2O towards the Northern Hemisphere (NH) is on the average two times faster than to the Southern Hemisphere (SH) with a mean speed of 1.15 m s−1 at 100 hPa. Furthermore, the speed towards the NH shows much more interannual variability with an amplitude of about 21% whilst the speed towards the SH varies by only 10%. An amplitude of 21% is also observed in the variability of the ascent rate at the Equator which is on the average 0.2 mm s−1.

scholarly journals Effect of Exclusion of Anomalous Tropical Stations on Temperature Trends from a 63-Station Radiosonde Network, and Comparison with Other Analyses

2003 ◽  
Vol 16 (13) ◽  
pp. 2288-2295 ◽  
Author(s):  
James K. Angell
Keyword(s):  
Global Changes ◽  
Station Network ◽  
Temperature Trends ◽  
A Value ◽  
Microwave Sounding Unit ◽  
Microwave Sounding ◽  
Stratospheric Cooling ◽  
The Tropics ◽  
Large Standard Error

Abstract A 63-station radiosonde network has been used for many years to estimate temperature variations and trends at the surface and in the 850–300-, 300–100-, and 100–50-mb layers of climate zones, both hemispheres, and the globe, but with little regard for the quality of individual station data. In this paper, nine tropical radiosonde stations in this network are identified as anomalous based on unrepresentatively large standard-error-of-regression values for 300–100-mb trends for the period 1958–2000. In the Tropics the exclusion of the 9 anomalous stations from the 63-station network for 1958–2000 results in a warming of the 300–100-mb layer rather than a cooling, a doubling of the warming of the 850–300-mb layer to a value of 0.13 K decade−1, and a greater warming at 850–300-mb than at the surface. The global changes in trend are smaller, but include a change to the same warming of the surface and the 850–300-mb layer during 1958–2000. The effect of the station exclusions is much less for 1979–2000, suggesting that most of the data problems are before this time. Temperature trends based on the 63-station network are compared with the Microwave Sounding Unit (MSU) and other radiosonde trends, and agreement is better after the exclusion of the anomalous stations. There is consensus that in the Tropics the troposphere has warmed slightly more than the surface during 1958–2000, but that there has been a warming of the surface relative to the troposphere during 1979–2000. Globally, the warming of the surface and the troposphere are essentially the same during 1958–2000, but during 1979–2000 the surface warms more than the troposphere. During the latter period the radiosondes indicate considerably more low-stratospheric cooling in the Tropics than does the MSU.

Error Structure and Atmospheric Temperature Trends in Observations from the Microwave Sounding Unit

2009 ◽  
Vol 22 (7) ◽  
pp. 1661-1681 ◽  
Author(s):  
Cheng-Zhi Zou ◽  
Mei Gao ◽  
Mitchell D. Goldberg
Keyword(s):  
Lower Stratosphere ◽  
Weather Conditions ◽  
Atmospheric Temperature ◽  
The Arctic ◽  
Polar Regions ◽  
Climate Trends ◽  
Orbital Geometry ◽  
Microwave Sounding Unit ◽  
Order Of Magnitude ◽  
Microwave Sounding

Abstract The Microwave Sounding Unit (MSU) onboard the National Oceanic and Atmospheric Administration polar-orbiting satellites measures the atmospheric temperature from the surface to the lower stratosphere under all weather conditions, excluding precipitation. Although designed primarily for monitoring weather processes, the MSU observations have been extensively used for detecting climate trends, and calibration errors are a major source of uncertainty. To reduce this uncertainty, an intercalibration method based on the simultaneous nadir overpass (SNO) matchups for the MSU instruments on satellites NOAA-10, -11, -12, and -14 was developed. Due to orbital geometry, the SNO matchups are confined to the polar regions, where the brightness temperature range is slightly smaller than the global range. Nevertheless, the resulting calibration coefficients are applied globally to the entire life cycle of an MSU satellite. Such intercalibration reduces intersatellite biases by an order of magnitude compared to prelaunch calibration and, thus, results in well-merged time series for the MSU channels 2, 3, and 4, which respectively represent the deep layer temperature of the midtroposphere (T2), tropopause (T3), and lower stratosphere (T4). Focusing on the global atmosphere over ocean surfaces, trends for the SNO-calibrated T2, T3, and T4 are, respectively, 0.21 ± 0.07, 0.08 ± 0.08, and −0.38 ± 0.27 K decade−1 from 1987 to 2006. These trends are independent of the number of limb-corrected footprints used in the dataset, and trend differences are marginal for varying bias correction techniques for merging the overlapping satellites on top of the SNO calibration. The spatial pattern of the trends reveals the tropical midtroposphere to have warmed at a rate of 0.28 ± 0.19 K decade−1, while the Arctic atmosphere warmed 2 to 3 times faster than the global average. The troposphere and lower stratosphere, however, cooled across the southern Indian and Atlantic Oceans adjacent to the Antarctic continent. To remove the stratospheric cooling effect in T2, channel trends from T2 and T3 (T23) and T2 and T4 (T24) were combined. The trend patterns for T23 and T24 are in close agreement, suggesting internal consistencies for the trend patterns of the three channels.

scholarly journals The Seasonal Cycle and Interannual Variability in Stratospheric Temperatures and Links to the Brewer–Dobson Circulation: An Analysis of MSU and SSU Data

2011 ◽  
Vol 24 (23) ◽  
pp. 6243-6258 ◽  
Author(s):  
Paul J. Young ◽  
David W. J. Thompson ◽  
Karen H. Rosenlof ◽  
Susan Solomon ◽  
Jean-François Lamarque
Keyword(s):  
Interannual Variability ◽  
Time Scales ◽  
High Latitude ◽  
Seasonal Cycle ◽  
Lower Stratosphere ◽  
Phase Relationship ◽  
Cold Season ◽  
Global Scale ◽  
Temperature Variability ◽  
Opposite Hemisphere

Abstract Previous studies have shown that lower-stratosphere temperatures display a near-perfect cancellation between tropical and extratropical latitudes on both annual and interannual time scales. The out-of-phase relationship between tropical and high-latitude lower-stratospheric temperatures is a consequence of variability in the strength of the Brewer–Dobson circulation (BDC). In this study, the signal of the BDC in stratospheric temperature variability is examined throughout the depth of the stratosphere using data from the Stratospheric Sounding Unit (SSU). While the BDC has a seemingly modest signal in the annual cycle in zonal-mean temperatures in the mid- and upper stratosphere, it has a pronounced signal in the month-to-month and interannual variability. Tropical and extratropical temperatures are significantly negatively correlated in all SSU channels on interannual time scales, suggesting that variations in wave driving are a major factor controlling global-scale temperature variability not only in the lower stratosphere (as shown in previous studies), but also in the mid- and upper stratosphere. The out-of-phase relationship between tropical and high latitudes peaks at all levels during the cold-season months: December–March in the Northern Hemisphere and July–October in the Southern Hemisphere. In the upper stratosphere, the out-of-phase relationship with high-latitude temperatures extends beyond the tropics and well into the extratropics of the opposite hemisphere. The seasonal cycle in stratospheric temperatures follows the annual march of insolation at all levels and latitudes except in the mid- to upper tropical stratosphere, where it is dominated by the semiannual oscillation. Mid- to upper-stratospheric temperatures also exhibit a distinct but small semiannual cycle at extratropical latitudes.

scholarly journals Exploring causes of interannual variability in the seasonal cycles of tropospheric nitrous oxide

2011 ◽  
Vol 11 (8) ◽  
pp. 3713-3730 ◽  
Author(s):  
C. D. Nevison ◽  
E. Dlugokencky ◽  
G. Dutton ◽  
J. W. Elkins ◽  
P. Fraser ◽  
...  
Keyword(s):  
Nitrous Oxide ◽  
Interannual Variability ◽  
Empirical Evidence ◽  
Southern Hemisphere ◽  
Seasonal Cycle ◽  
Coastal Upwelling ◽  
Transport Model ◽  
Seasonal Cycles ◽  
Stratospheric Temperature

Abstract. Seasonal cycles in the mixing ratios of tropospheric nitrous oxide (N2O) are derived by detrending long-term measurements made at sites across four global surface monitoring networks. The detrended monthly data display large interannual variability, which at some sites challenges the concept of a "mean" seasonal cycle. In the Northern Hemisphere, correlations between polar winter lower stratospheric temperature and detrended N2O data, around the month of the seasonal minimum, provide empirical evidence for a stratospheric influence, which varies in strength from year to year and can explain much of the interannual variability in the surface seasonal cycle. Even at sites where a strong, competing, regional N2O source exists, such as from coastal upwelling at Trinidad Head, California, the stratospheric influence must be understood to interpret the biogeochemical signal in monthly mean data. In the Southern Hemisphere, detrended surface N2O monthly means are correlated with polar spring lower stratospheric temperature in months preceding the N2O minimum, providing empirical evidence for a coherent stratospheric influence in that hemisphere as well, in contrast to some recent atmospheric chemical transport model (ACTM) results. Correlations between the phasing of the surface N2O seasonal cycle in both hemispheres and both polar lower stratospheric temperature and polar vortex break-up date provide additional support for a stratospheric influence. The correlations discussed above are generally more evident in high-frequency in situ data than in data from weekly flask samples. Furthermore, the interannual variability in the N2O seasonal cycle is not always correlated among in situ and flask networks that share common sites, nor do the mean seasonal amplitudes always agree. The importance of abiotic influences such as the stratospheric influx and tropospheric transport on N2O seasonal cycles suggests that, at sites remote from local sources, surface N2O mixing ratio data by themselves are unlikely to provide information about seasonality in surface sources, e.g., for atmospheric inversions, unless the ACTMs employed in the inversions accurately account for these influences. An additional abioitc influence is the seasonal ingassing and outgassing of cooling and warming surface waters, which creates a thermal signal in tropospheric N2O that is of particular importance in the extratropical Southern Hemisphere, where it competes with the biological ocean source signal.

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

2017 ◽  
Vol 30 (15) ◽  
pp. 6005-6016 ◽  
Author(s):  
Fang Pan ◽  
Xianglei Huang ◽  
Stephen S. Leroy ◽  
Pu Lin ◽  
L. Larrabee Strow ◽  
...  
Keyword(s):  
Cooling Rate ◽  
Lower Stratosphere ◽  
Natural Variability ◽  
Atmospheric Infrared Sounder ◽  
Stratospheric Temperature ◽  
Temperature Trends ◽  
Microwave Sounding Unit ◽  
Microwave Sounding ◽  
Microwave Radiances ◽  
Global Mean

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.

scholarly journals The Radiometric Sensitivity Requirements for Satellite Microwave Temperature Sounding Instruments for Numerical Weather Prediction

2010 ◽  
Vol 27 (3) ◽  
pp. 443-456 ◽  
Author(s):  
William Bell ◽  
Sabatino Di Michele ◽  
Peter Bauer ◽  
Tony McNally ◽  
Stephen J. English ◽  
...  
Keyword(s):  
Southern Hemisphere ◽  
Weather Prediction ◽  
Forecast Accuracy ◽  
Forecast Errors ◽  
Atmospheric Infrared Sounder ◽  
Microwave Sounding Unit ◽  
Atmospheric Sounding ◽  
Microwave Sounding ◽  
Satellite Microwave ◽  
The Impact

Abstract The sensitivity of NWP forecast accuracy with respect to the radiometric performance of microwave sounders is assessed through a series of observing system experiments at the Met Office and ECMWF. The observing system experiments compare the impact of normal data from a single Advanced Microwave Sounding Unit (AMSU) with that from an AMSU where synthetic noise has been added. The results show a measurable reduction in forecast improvement in the Southern Hemisphere, with improvements reduced by 11% for relatively small increases in radiometric noise [noise-equivalent brightness temperature (NEΔT) increased from 0.1 to 0.2 K for remapped data]. The impact of microwave sounding data is shown to be significantly less than was the case prior to the use of advanced infrared sounder data [Atmospheric Infrared Sounder (AIRS) and Infrared Atmospheric Sounding Interferometer (IASI)], with microwave sounding data now reducing Southern Hemisphere forecast errors by approximately 10% compared to 40% in the pre-AIRS/IASI period.

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