The Experts below are selected from a list of 11508 Experts worldwide ranked by ideXlab platform
J W Waters - One of the best experts on this subject based on the ideXlab platform.
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an atmospheric Tape Recorder the imprint of tropical tropopause temperatures on stratospheric water vapor
Journal of Geophysical Research, 1996Co-Authors: Philip W Mote, Karen H Rosenlof, Michael E Mcintyre, Ewan S Carr, John C Gille, James R Holton, Jonathan S Kinnersley, H C Pumphrey, James M Russell, J W WatersAbstract:We describe observations of tropical stratospheric water vapor q that show clear evidence of large-scale upward advection of the signal from annual fluctuations in the effective "entry mixing ratio" qE of air entering the tropical stratosphere. In other words, air is "marked," on emergence above the highest cloud tops, like a signal recorded on an upward moving magnetic Tape. We define qE as the mean water vapor mixing ratio, at the tropical tropopause, of air that will subsequently rise and enter the stratospheric "overworld" at about 400 K. The observations show a systematic phase lag, increasing with altitude, between the annual cycle in qE and the annual cycle in q at higher altitudes. The observed phase lag agrees with the phase lag calculated assuming advection by the transformed Eulerian-mean vertical velocity of a qE crudely estimated from 100-hPa temperatures, which we use as a convenient proxy for tropopause temperatures. The phase agreement confirms the overall robustness of the calculation and strongly supports the Tape Recorder hypothesis. Establishing a quantitative link between qE and observed tropopause temperatures, however, proves difficult because the process of marking the Tape depends subtly on both small- and large-scale processes. The Tape speed, or large-scale upward advection speed, has a substantial annual variation and a smaller variation due to the quasi-biennial oscillation, which delays or accelerates the arrival of the signal by a month or two in the middle stratosphere. As the Tape moves upward, the signal is attenuated with an e-folding time of about 7 to 9 months between 100 and 50 hPa and about 15 to 18 months between 50 and 20 hPa, constraining possible orders of magnitude both of vertica.1 diffusion Kand of ra.tes of mixing in from the extratropics. For instance, if there were no mixing in, then Kwould be in the range 0.03-0.09 ms-; this is an upper bound on Ifs.
Katrin M Nissen - One of the best experts on this subject based on the ideXlab platform.
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the role of the south east asian monsoon and other seasonal features in creating the Tape Recorder signal in the unified model
Quarterly Journal of the Royal Meteorological Society, 2004Co-Authors: Ross N Bannister, A. R. Gregory, A Oneill, Katrin M NissenAbstract:A multi-year simulation with an atmospheric general-circulation model (AGCM), the Unified Model, is shown to simulate the main features of seasonal variations in the concentrations of water vapour in the stratosphere—the so-called Tape-Recorder signal. An off-line transport model, utilizing winds from the AGCM, is used to synthesize the signal from local contributions. During June–July–August, the most significant localized contribution to the moist phase of the signal comes from an air stream emanating from the South-East Asian monsoon. The moist air does not enter the stratosphere immediately above the monsoon in a localized ‘fountain’. Rather, the air stream moves southward, via the monsoon's upper level anticyclone, into the tropical stratosphere while moving steadily upwards across isentropic surfaces in a field of radiative heating in the tropical tropopause layer (TTL). As a result of this steady ascent during equatorward movement, not all the airstream is freeze dried in the cold cap of low temperatures which exists in the TTL above the monsoon. The water vapour mixing ratios of air entering the stratospheric Tape-Recorder are therefore not entirely set by the minimum temperatures near the equator, but in part by physical conditions outside the inner tropical region used to define the Tape-Recorder signal. During December–January–February, the flow near the tropopause is simpler. Dry air enters the stratosphere by slow upglide through the localized temperature minimum near the tropical tropopause over the western Pacific. The mixing ratios during the dry phase are set largely by freeze drying in this region. The simple Tape-Recorder model, which envisages that mixing ratios are set by the minimum temperature near the tropical tropopause is therefore an oversimplification. Copyright © 2004 Royal Meteorological Society
A. R. Gregory - One of the best experts on this subject based on the ideXlab platform.
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the role of the south east asian monsoon and other seasonal features in creating the Tape Recorder signal in the unified model
Quarterly Journal of the Royal Meteorological Society, 2004Co-Authors: Ross N Bannister, A. R. Gregory, A Oneill, Katrin M NissenAbstract:A multi-year simulation with an atmospheric general-circulation model (AGCM), the Unified Model, is shown to simulate the main features of seasonal variations in the concentrations of water vapour in the stratosphere—the so-called Tape-Recorder signal. An off-line transport model, utilizing winds from the AGCM, is used to synthesize the signal from local contributions. During June–July–August, the most significant localized contribution to the moist phase of the signal comes from an air stream emanating from the South-East Asian monsoon. The moist air does not enter the stratosphere immediately above the monsoon in a localized ‘fountain’. Rather, the air stream moves southward, via the monsoon's upper level anticyclone, into the tropical stratosphere while moving steadily upwards across isentropic surfaces in a field of radiative heating in the tropical tropopause layer (TTL). As a result of this steady ascent during equatorward movement, not all the airstream is freeze dried in the cold cap of low temperatures which exists in the TTL above the monsoon. The water vapour mixing ratios of air entering the stratospheric Tape-Recorder are therefore not entirely set by the minimum temperatures near the equator, but in part by physical conditions outside the inner tropical region used to define the Tape-Recorder signal. During December–January–February, the flow near the tropopause is simpler. Dry air enters the stratosphere by slow upglide through the localized temperature minimum near the tropical tropopause over the western Pacific. The mixing ratios during the dry phase are set largely by freeze drying in this region. The simple Tape-Recorder model, which envisages that mixing ratios are set by the minimum temperature near the tropical tropopause is therefore an oversimplification. Copyright © 2004 Royal Meteorological Society
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The sensitivity of a model's stratospheric Tape Recorder to the choice of advection scheme
Quarterly Journal of the Royal Meteorological Society, 2002Co-Authors: A. R. Gregory, V. WestAbstract:The sensitivity of a climate model's transport to the choice of numerical advection scheme is investigated using simulations of the stratospheric Tape Recorder. Significant differences are found between tracers advected with the Heun scheme (with centred spatial differencing) and tracers advected with a flux-limited total variation diminishing (TVD) scheme. The Tape Recorder simulated by the TVD scheme propagates upwards unrealistically fast: about three times faster than the Tape Recorder of the Heun scheme, even though the winds are identical. In contrast, the amplitude of the TVD scheme's Tape Recorder is more realistic than that of the Heun scheme, which is too strong in the middle stratosphere. Further off-line tracer experiments, using a family of conservative, upwind advection schemes, demonstrate how the Tape Recorder's phase speed decreases as the order of the polynomial representing the tracer's subgrid variation is increased. It is found that schemes with more implicit vertical diffusion than a quasi third-order scheme produce a Tape Recorder with unacceptably fast upwards propagation. The sensitivity can only be reproduced in a one-dimensional model when winds with strong variability are used, highlighting a limitation of the traditional advection tests that use constant winds. The experiments also show that the numerical oscillations produced by non-monotonic methods, including the Heun scheme, can artificially strengthen the Tape-Recorder signal resulting in a unrealistic lack of attenuation with height. Finally, a full climate simulation using a higher-order, monotonic advection scheme is found to produce a Tape Recorder that is reasonably realistic, both in speed and amplitude. Copyright © 2002 Royal Meteorological Society
Thomas Birner - One of the best experts on this subject based on the ideXlab platform.
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Role of vertical and horizontal mixing in the Tape Recorder signal near the tropical tropopause
Atmospheric Chemistry and Physics, 2017Co-Authors: Anne A. Glanville, Thomas BirnerAbstract:Abstract. Nearly all air enters the stratosphere through the tropical tropopause layer (TTL). The TTL therefore exerts a control on stratospheric chemistry and climate. The hemispheric meridional overturning (Brewer–Dobson) circulation spreads this TTL influence upward and poleward. Stratospheric water vapor concentrations are set near the tropical tropopause and are nearly conserved in the lowermost stratosphere. The resulting upward propagating tracer transport signal of seasonally varying entry concentrations is known as the Tape Recorder signal. Here, we study the roles of vertical and horizontal mixing in shaping the Tape Recorder signal in the tropical lowermost stratosphere, focusing on the 80 hPa level. We analyze the Tape Recorder signal using data from satellite observations, a reanalysis, and a chemistry–climate model (CCM). By modifying past methods, we are able to capture the seasonal cycle of effective vertical transport velocity in the tropical lowermost stratosphere. Effective vertical transport velocities are found to be multiple times stronger than residual vertical velocities for the reanalysis and the CCM. We also study the Tape Recorder signal in an idealized 1-D transport model. By performing a parameter sweep, we test a range of different strengths of transport contributions by vertical advection, vertical mixing, and horizontal mixing. By introducing seasonality into the transport strengths, we find that the most successful simulation of the observed Tape Recorder signal requires vertical mixing at 80 hPa that is multiple times stronger compared to previous estimates in the literature. Vertical mixing is especially important during boreal summer when vertical advection is weak. Simulating the reanalysis Tape Recorder requires excessive amounts of vertical mixing compared to observations but also to the CCM, which hints at the role of spurious dispersion due to data assimilation. Contrasting the results between pressure and isentropic coordinates allows for further insights into quasi-adiabatic vertical mixing, e.g., associated with overshooting convection or breaking gravity waves. Horizontal mixing, which takes place primarily along isentropes due to Rossby wave breaking, is captured more consistently in isentropic coordinates. Overall, our study emphasizes the role of vertical mixing in lowermost tropical stratospheric transport, which appears to be as important as vertical advection by the residual mass circulation. This questions the perception of the Tape Recorder as a manifestation of slow upward transport as opposed to a phenomenon influenced by quick and intense transport through mixing, at least near the Tape head. However, due to the limitations of the observational dataset used and the simplicity of the applied transport model, further work is required to more clearly specify the role of vertical mixing in lowermost stratospheric transport in the tropics.
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Role of vertical and horizontal mixing in the Tape Recorder signal near the tropical tropopause
2016Co-Authors: Anne A. Glanville, Thomas BirnerAbstract:Abstract. Nearly all air enters the stratosphere through the tropical tropopause layer (TTL). The TTL therefore exerts a control on stratospheric chemistry and climate. The hemispheric meridional overturning (Brewer-Dobson) circulation spreads this TTL influence upward and poleward. Stratospheric water vapor concentrations are set near the tropical tropopause and are nearly conserved in the lowermost stratosphere. The resulting upward propagating tracer transport signal of seasonally varying entry concentrations is known as the Tape Recorder signal. Here, we study the roles of vertical and horizontal mixing in shaping the Tape Recorder signal in the tropical lowermost stratosphere. We analyze the Tape Recorder signal using data from satellite observations, a reanalysis, and a chemistry-climate model (CCM). Modifying past methods, we are able to capture the seasonal cycle of effective vertical transport velocity in the tropical lowermost stratosphere, which is found to be multiple times stronger than residual vertical velocities for the reanalysis and the CCM. We also study the Tape Recorder signal in an idealized one-dimensional transport model. By performing a parameter-sweep we test a range of different strengths of transport contributions by vertical advection, vertical mixing, and horizontal mixing. Introducing seasonality in the transport strengths we find that the most successful simulation of the observed Tape Recorder signal requires quadrupled vertical mixing in the lowermost tropical stratosphere compared to previous estimates in the literature. Vertical mixing is especially important during boreal summer when vertical advection is weak. The reanalysis requires excessive amounts of vertical mixing compared to observations but also to the CCM, which hints at the role of spurious dispersion due to data assimilation. Contrasting the results between pressure and isentropic coordinates allows further insights into quasi-adiabatic vertical mixing, e.g. associated with breaking gravity waves. Horizontal mixing, which takes place primarily along isentropes due to Rossby wave breaking, is captured more consistently in isentropic coordinates. Overall our study emphasizes the role of vertical mixing in lowermost tropical stratospheric transport, which appears to be as important as vertical advection by the residual mass circulation. This questions the perception of the "Tape Recorder" as a manifestation of slow upward transport as opposed to a phenomenon influenced by quick and intense transport through mixing, at least near the Tape head.
Philip W Mote - One of the best experts on this subject based on the ideXlab platform.
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an atmospheric Tape Recorder the imprint of tropical tropopause temperatures on stratospheric water vapor
Journal of Geophysical Research, 1996Co-Authors: Philip W Mote, Karen H Rosenlof, Michael E Mcintyre, Ewan S Carr, John C Gille, James R Holton, Jonathan S Kinnersley, H C Pumphrey, James M Russell, J W WatersAbstract:We describe observations of tropical stratospheric water vapor q that show clear evidence of large-scale upward advection of the signal from annual fluctuations in the effective "entry mixing ratio" qE of air entering the tropical stratosphere. In other words, air is "marked," on emergence above the highest cloud tops, like a signal recorded on an upward moving magnetic Tape. We define qE as the mean water vapor mixing ratio, at the tropical tropopause, of air that will subsequently rise and enter the stratospheric "overworld" at about 400 K. The observations show a systematic phase lag, increasing with altitude, between the annual cycle in qE and the annual cycle in q at higher altitudes. The observed phase lag agrees with the phase lag calculated assuming advection by the transformed Eulerian-mean vertical velocity of a qE crudely estimated from 100-hPa temperatures, which we use as a convenient proxy for tropopause temperatures. The phase agreement confirms the overall robustness of the calculation and strongly supports the Tape Recorder hypothesis. Establishing a quantitative link between qE and observed tropopause temperatures, however, proves difficult because the process of marking the Tape depends subtly on both small- and large-scale processes. The Tape speed, or large-scale upward advection speed, has a substantial annual variation and a smaller variation due to the quasi-biennial oscillation, which delays or accelerates the arrival of the signal by a month or two in the middle stratosphere. As the Tape moves upward, the signal is attenuated with an e-folding time of about 7 to 9 months between 100 and 50 hPa and about 15 to 18 months between 50 and 20 hPa, constraining possible orders of magnitude both of vertica.1 diffusion Kand of ra.tes of mixing in from the extratropics. For instance, if there were no mixing in, then Kwould be in the range 0.03-0.09 ms-; this is an upper bound on Ifs.
