Changes In Tropopause Height Research Articles

Behavior of tropopause height and atmospheric temperature in models, reanalyses, and observations: Decadal changes

We examine changes in tropopause height, a variable that has hitherto been neglected in climate change detection and attribution studies. The pressure of the lapse rate tropopause, pLRT, is diagnosed from reanalyses and from integrations performed with coupled and uncoupled climate models. In the National Centers for Environmental Prediction (NCEP) reanalysis, global‐mean pLRT decreases by 2.16 hPa/decade over 1979–2000, indicating an increase in the height of the tropopause. The shorter European Centre for Medium‐Range Weather Forecasts (ECMWF) reanalysis has a global‐mean pLRT trend of −1.13 hPa/decade over 1979–1993. Simulated pLRT trends over the past several decades are consistent with reanalysis results. Superimposed on the overall increase in tropopause height in models and reanalyses are pronounced height decreases following the eruptions of El Chichón and Pinatubo. Interpreting these pLRT results requires knowledge of both T(z), the initial atmospheric temperature profile, and ΔT(z), the change in this profile in response to external forcing. T(z) has a strong latitudinal dependence, as does ΔT(z) for forcing by well‐mixed greenhouse gases and stratospheric ozone depletion. These dependencies help explain why overall tropopause height increases in reanalyses and observations are amplified toward the poles. The pronounced increases in tropopause height in the climate change integrations considered here indicate that even AGCMs with coarse vertical resolution can resolve relatively small externally forced changes in tropopause height. The simulated decadal‐scale changes in pLRT are primarily thermally driven and are an integrated measure of the anthropogenically forced warming of the troposphere and cooling of the stratosphere. Our algorithm for estimating pLRT (based on a thermal definition of tropopause height) is sufficiently sensitive to resolve these large‐scale changes in atmospheric thermal structure. Our results indicate that the simulated increase in tropopause height over 1979–1997 is a robust, zero‐order response of the climate system to forcing by well‐mixed greenhouse gases and stratospheric ozone depletion. At the global‐mean level, we find agreement between the simulated decadal‐scale pLRT changes and those estimated from reanalyses. While the agreement between simulated pLRT changes and those in NCEP is partly fortuitous (due to excessive stratospheric cooling in NCEP), it is also driven by real pattern similarities. Our work illustrates that changes in tropopause height may be a useful “fingerprint” of human effects on climate and are deserving of further attention.

Effect of tropopause height changes on the calculation of ozone trends and their radiative forcing

Three separate estimates of ozone trends since 1970 are obtained from ozonesonde analyses in the Northern Hemisphere, at up to 11 point locations. Our analysis shows that there has been an increase in the annually averaged tropopause height of between 330–520 m at all stations, accompanied by an overall upward movement of the ozone profile. This movement of the ozone profile has led to an extra 2–15% decade−1 ozone depletion between roughly 8 and 22 km. We argue that as the part of the ozone trend associated with “dynamical” movement of the ozone profile is not a direct result of anthropogenic chemical ozone depletion, it ought not to be included in anthropogenic radiative forcing calculations. This leads to a stratospheric ozone radiative forcing which is roughly 50% of the original estimate. Combining stratospheric and tropospheric ozone changes to calculate the total ozone radiative forcing in the Northern Hemisphere for the 1970–1997 period gives a radiative forcing of −0.09 W m−2, excluding the effects of dynamical movement of the ozone profile, which were calculated to have led to a further “ozone feedback” of −0.1 W m−2. These results suggest estimating ozone radiative forcing from observational ozone trend data, without accounting for the movement of the ozone profile could be fundamentally flawed, due to the unquantified feedbacks in the climate system, making it difficult to separate out the part of the ozone trend associated directly with the anthropogenic forcing.

Long-term trend of tropopause

Due to the depletion of O 3, less heat would be absorbed in the stratosphere and due to the increase in CO 2 content, more heat would be trapped in the atmosphere. These effects may change the thermal structure of the tropopause region. Radiosonde observations taken during the past 9–32 years at four stations in India have been analysed to examine the long-term trend of tropopause height (TPH) and tropopause temperature (TPT). These stations are New Delhi (28°N, 77°E), Thiruvananthapuram (8°N, 76°E), Patna (25°N, 85°E) and Ahmedabad (24°N, 72°E). The results show that these parameters are changing over the years. The trend of change is not same throughout the period of study. Before and after around 1972, the trends are found to be different. Considering the whole period of data we find that TPH changes from +0.57 to + 3.25 %/decade, TPT has a decreasing trend for New Delhi (−0.57%/decade) and Thiruvananthapuram (−0.94%/decade) and an increasing trend for Patna (+2.12%/decade) and Ahmedabad (+1.22%/decade).

Seasonal acceleration of the rate of total ozone decreases over Central Europe: impact of tropopause height changes

Total ozone data from some European stations have been analyzed to detect the ozone decrease in different seasons from 1979 to 1995. The differences between the winter–spring (December–March) and summer (May–August) total ozone means have decreased distinctly during the last three decades, by ∼10 Dobson Units per decade, showing that the winter–spring decrease is significantly stronger than the summer one. Applying a multiple regression model to the monthly means of tropopause height, positive trends in the summer and winter–spring seasons have been found, especially since 1979. This corresponds to the accelerating ozone decrease then. The possibility of using tropopause height variations as an indicator of dynamical variability in the total ozone trend model is discussed. The total ozone response to the changes of tropopause height seems to be independent of timescale over which the tropopause-total ozone relationship has been examined (month-to-month, interannual). The total ozone trends, as well as the accelerated rate of ozone decrease since 1979 in the winter–spring and summer seasons, respectively, are reduced by about 0.5–1% per decade after inclusion of the tropopause height effect on the ozone model.

The effect of tropopause height on the content of radioactive debris in surface atmosphere

The effect of tropopause height on the content of 137Cs and total beta activity in surface atmosphere was considered for the period of intensive nuclear weapon tests, from 1968–1971. The activity of 137Cs in monthly air filter samples was measured by gamma spectrometry and total beta activity was determined by 2π proportional counters. The results were correlated with data on tropopause height. The results indicate that the movement of radioactive debris from the stratosphere into the troposphere occurs simultaneously with the changes in tropopause height. The content of long lived radionuclides in the troposphere follows the changes with a certain delay due to meteorological conditions in surface air and due to the location of sampling.

Dynamical Response of the Tropical Total Ozone to Sea Surface Temperature Changes

Interannual variations of total ozone in the equatorial region are discussed in terms of the lower-stratospheric dynamical processes associated with sea surface temperature (SST) changes on an El Nino-Southern Oscillation time scale. Tropospheric diabatic heating by the latent heat release in convective systems drives the interannual variations of tropopause height and atmospheric vertical motions. The adiabatic cooling associated with the dynamically forced ascending motion is subject to radiative heating, which further extends the upwelling motion into the stratosphere. SST variations can thus influence total ozone amounts by changing the tropopause height and vertical advection through modulation of tropospheric diabatic heating. Mechanistic relationships that describe total ozone fluctuations through the advection effect and the tropopause effect of SST variations are derived using the equivalent potential temperature. Total ozone fluctuations are estimated using a quantitative formulation of these mechanistic equations together with the observed SST data. These results indicate that the interannual variations of the zonal wave component of equatorial total ozone are governed by the tropopause effect of SST variations. Preliminary investigation suggests that the annual cycle of tropical total ozone is coupled to the tropopause height changes under the influence of the planetary wave-induced lower-stratospheric temperature rather than local SST.

Tropopause Folding and the Variability of the Tropopause Height as Seen by the Flatland VHF Radar

Abstract The Flatland radar, a VHF wind profiler located near Urbana, Illinois, has been used to study the variability of the tropopause over the period March 1987–April 1988. The vertically directed radar beam provides an indicator of tropopause height as well as measurements of the vertical velocity of the air. The sudden tropopause height changes previously seen in special campaigns are found to be relatively common features. Several case studies made under varying synoptic conditions are used to show that thew discontinuities are associated with tropopause folding events as revealed by cross-section analyses of potential temperature and potential vorticity based on radiosonde data. The vertical velocity in a typical tropopause fold is downward at up to 15 cm s−1. Finally, applications of the continuous data from VHF radars to develop quantitative climatologies of tropopause folding events are presented.

The Threefold Structure of the Atmosphere and the Characteristics of the Tropopause

All available soundings for January 1, 1956 have been studied with respect to their tropospheric and stratospheric temperature structure and with emphasis on the height and form of the tropopause. It was found that the latitudinal influence on the total vertical structure of the soundings was not dominating, but rather the location of soundings with respect to the two main westwind maxima (polarfront jet and subtropical jet) of the westerlies seemed to be important. A selection of soundings according to this principle (north of polarfront jet, between the two jets, south of subtropical jet) made it possible to distinguish between different types of soundings. This fundamental difference is discussed and will form the basis for future studies of world wide circulation changes. Furthermore the distribution of tropopause height and temperature has been mapped and studied on a hemispheric scale. Each of the above mentioned types possesses a typical vertical temperature structure and a characteristic tropopause heigth. Two rapid changes in tropopause height (tropopause breaklines) connected with the main westwind belts separate areas possessing an almost uniform tropopause level. Inside each of these areas a remarkable quasi-barotropic state of the upper tropospheric layers is shown. Similar discussion has been devoted to the nature of soundings inside or close to the jets or the breaks in tropopause height. Here the soundings have a more complicated vertical structure and their interpretation becomes difficult. DOI: 10.1111/j.2153-3490.1957.tb01884.x

The Threefold Structure of the Atmosphere and the Characteristics of the Tropopause

All available soundings for January 1, 1956 have been studied with respect to their tropospheric and stratospheric temperature structure and with emphasis on the height and form of the tropopause. It was found that the latitudinal influence on the total vertical structure of the soundings was not dominating, but rather the location of soundings with respect to the two main westwind maxima (polarfront jet and subtropical jet) of the westerlies seemed to be important. A selection of soundings according to this principle (north of polarfront jet, between the two jets, south of subtropical jet) made it possible to distinguish between different types of soundings. This fundamental difference is discussed and will form the basis for future studies of world wide circulation changes. Furthermore the distribution of tropopause height and temperature has been mapped and studied on a hemispheric scale. Each of the above mentioned types possesses a typical vertical temperature structure and a characteristic tropopause heigth. Two rapid changes in tropopause height (tropopause breaklines) connected with the main westwind belts separate areas possessing an almost uniform tropopause level. Inside each of these areas a remarkable quasi-barotropic state of the upper tropospheric layers is shown.
 Similar discussion has been devoted to the nature of soundings inside or close to the jets or the breaks in tropopause height. Here the soundings have a more complicated vertical structure and their interpretation becomes difficult.