Zonally resolved water vapour coupling with tropical tropopause temperature: Seasonal and interannual variability, and influence of the Walker circulation

Abstract. A merged time series of stratospheric water vapour built from the Halogen Occultation Instrument (HALOE) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) data between 60° S and 60° N and 15 to 30 km and covering the years 1992 to 2012 was analysed by multivariate linear regression, including an 11-year solar cycle proxy. Lower stratospheric water vapour was found to reveal a phase-shifted anti-correlation with the solar cycle, with lowest water vapour after solar maximum. The phase shift is composed of an inherent constant time lag of about 2 years and a second component following the stratospheric age of air. The amplitudes of the water vapour response are largest close to the tropical tropopause (up to 0.35 ppmv) and decrease with altitude and latitude. Including the solar cycle proxy in the regression results in linear trends of water vapour being negative over the full altitude/latitude range, while without the solar proxy, positive water vapour trends in the lower stratosphere were found. We conclude from these results that a solar signal seems to be generated at the tropical tropopause which is most likely imprinted on the stratospheric water vapour abundances and transported to higher altitudes and latitudes via the Brewer–Dobson circulation. Hence it is concluded that the tropical tropopause temperature at the final dehydration point of air may also be governed to some degree by the solar cycle. The negative water vapour trends obtained when considering the solar cycle impact on water vapour abundances can possibly solve the "water vapour conundrum" of increasing stratospheric water vapour abundances despite constant or even decreasing tropopause temperatures.

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Diurnal Variability of Lower and Middle Atmospheric Water Vapour Over The Asian Summer Monsoon Region: First Results From COSMIC-1 and TIMED-SABER Measurements

10.21203/rs.3.rs-693267/v1 ◽

2021 ◽

Author(s):

Siddarth Shankar Das ◽

K N Uma ◽

K V Suneeth

Keyword(s):

Water Vapour ◽

Middle Atmosphere ◽

Asian Summer Monsoon ◽

Diurnal Variability ◽

Diurnal Amplitude ◽

Tropical Tropopause ◽

First Results ◽

Asian Summer ◽

Tropopause Temperature ◽

Stratospheric Water Vapour

Abstract First observations on the vertical structure of diurnal variability of tropospheric water vapour in the lower and middle atmosphere using 13 years of COSMIC and 18 years of SABER observations are presented in this paper. The most significant and new observation is that the middle stratospheric water vapour (SWV) enhancement is observed between 9-18 LT, whereas it is between 6-15 LT near tropopause in all the seasons. The diurnal amplitude of water vapour near tropopause is between 0.3-0.4 ppmv. Bimodal peaks are found in the diurnal amplitude of SWV, maximizing between 25-30 km (~0.4 ppmv) and 45-50 km (~0.6 ppmv). The analysis reveals that the diurnal variability in the lower SWV is controlled by the tropical tropopause temperature, whereas the middle and upper SWV is controlled by methane oxidation. The results are presented and discussed in the light of present understanding.

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Tropical convective transport and the Walker circulation

Atmospheric Chemistry and Physics ◽

10.5194/acp-12-9791-2012 ◽

2012 ◽

Vol 12 (20) ◽

pp. 9791-9797 ◽

Cited By ~ 13

Author(s):

J. S. Hosking ◽

M. R. Russo ◽

P. Braesicke ◽

J. A. Pyle

Keyword(s):

Climate Model ◽

Deep Convection ◽

Walker Circulation ◽

Reanalysis Data ◽

Convective Transport ◽

Boreal Winter ◽

Transport Pathways ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

The Walker Circulation

Abstract. We introduce a methodology to visualise rapid vertical and zonal tropical transport pathways. Using prescribed sea-surface temperatures in four monthly model integrations for 2005, we characterise preferred transport routes from the troposphere to the stratosphere in a high resolution climate model. Most efficient transport is modelled over the Maritime Continent (MC) in November and February, i.e., boreal winter. In these months, the ascending branch of the Walker Circulation over the MC is formed in conjunction with strong deep convection, allowing fast transport into the stratosphere. In the model the upper tropospheric zonal winds associated with the Walker Circulation are also greatest in these months in agreement with ERA-Interim reanalysis data. We conclude that the Walker circulation plays an important role in the seasonality of fast tropical transport from the lower and middle troposphere to the upper troposphere and so impacts at the same time the potential supply of surface emissions to the tropical tropopause layer (TTL) and subsequently to the stratosphere.

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Longitudinal Asymmetric Trends of Tropical Cold-Point Tropopause Temperature and Their Link to Strengthened Walker Circulation

Journal of Climate ◽

10.1175/jcli-d-15-0851.1 ◽

2016 ◽

Vol 29 (21) ◽

pp. 7755-7771 ◽

Cited By ~ 17

Author(s):

Dingzhu Hu ◽

Wenshou Tian ◽

Zhaoyong Guan ◽

Yipeng Guo ◽

Sandip Dhomse

Keyword(s):

Climate Model ◽

Walker Circulation ◽

Warm Pool ◽

Tropical Regions ◽

Model Simulations ◽

Tropical Tropopause Layer ◽

Tropical Tropopause ◽

Climate Model Simulations ◽

Cold Point ◽

Tropopause Temperature

Abstract The zonal structure of trends in the tropical tropopause layer during 1979–2014 is investigated by using reanalysis datasets and chemistry–climate model simulations. The analysis herein reveals that the tropical cold-point tropopause temperature (CPTT) trends during 1979–2014 are zonally asymmetric; that is, over the tropical central and eastern Pacific (CEP; 20°S–20°N, 160°E–100°W), the CPTT shows an increasing trend of 0.22 K decade−1, whereas over the rest of the tropical regions (non-CEP regions) the CPTT shows a decreasing trend of −0.08 K decade−1. Model simulations suggest that this zonal asymmetry in the tropical CPTT trends can be partly attributed to Walker circulation (WC) changes induced by zonally asymmetric changes of the sea surface temperatures (SSTs). The increasing (decreasing) SSTs over the western Pacific (CEP) result in a larger zonal gradient in sea level pressure over the tropical Pacific and intensified surface easterlies. The increased pressure gradient leads to enhanced convection over the Indo-Pacific warm pool and weakened convection over the CEP, facilitating a stronger WC. The downward branch of the intensified WC induces a dynamical warming over the CEP and the upward branch of the intensified WC induces a dynamical cooling over the non-CEP regions below 150 hPa. The significant warming in the upper troposphere and lower stratosphere (UTLS) caused by the WC descending and wave activity changes in the UTLS over the CEP shifts the cold-point tropopause height to a higher level, while the radiative effects of greenhouse gases, ozone, and water vapor changes in the UTLS make less important contributions to the trend of the tropical CPTT than SST changes.

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Decadal Variability of Asian–Australian Monsoon–ENSO–TBO Relationships

Journal of Climate ◽

10.1175/2011jcli4015.1 ◽

2011 ◽

Vol 24 (18) ◽

pp. 4925-4940 ◽

Cited By ~ 35

Author(s):

Gerald A. Meehl ◽

Julie M. Arblaster

Keyword(s):

Indian Ocean ◽

Interannual Variability ◽

Walker Circulation ◽

Climate System ◽

Asia Pacific ◽

Pacific Region ◽

Trade Winds ◽

Australian Monsoon ◽

The Walker Circulation ◽

Sst Anomalies

Abstract A set of dynamically coupled ocean–atmosphere mechanisms has previously been proposed for the Asia–Pacific tropics to produce a dominant biennial component of interannual variability [the tropospheric biennial oscillation (TBO)]. Namely, a strong Asian–Australian monsoon is often associated with negative SST anomalies in the equatorial eastern Pacific and a negative Indian Ocean dipole in northern fall between the strong Indian monsoon and strong Australian monsoon, and tends to be followed by a weak monsoon and positive SST anomalies in the Pacific the following year and so on. These connections are communicated through the large-scale east–west (Walker) circulation that involves the full depth of the troposphere. However, the Asia–Pacific climate system is characterized by intermittent decadal fluctuations whereby the TBO during some time periods is more pronounced than others. Observations and models are analyzed to identify processes that make the system less biennial at certain times due to one or some combination of the following:increased latitudinal extent of Pacific trade winds and wider cold tongue;warmer tropical Pacific compared to tropical Indian Ocean that weakens trade winds and reduces coupling strength;eastward shift of the Walker circulation;reduced interannual variability of Pacific and/or Indian Ocean SSTs. Decadal time-scale SST variability associated with the interdecadal Pacific oscillation (IPO) has been shown to alter the TBO over the Indo-Pacific region by contributing changes in either some or all of the four factors listed above. Analysis of a multicentury control run of the Community Climate System Model, version 4 (CCSM4), shows that this decadal modulation of interannual variability is transferred via the Walker circulation to the Asian–Australian monsoon region, thus affecting the TBO and monsoon–Pacific connections. Understanding these processes is important to be able to evaluate decadal predictions and longer-term climate change in the Asia–Pacific region.

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A solar signal in lower stratospheric water vapour?

Atmospheric Chemistry and Physics Discussions ◽

10.5194/acpd-15-12353-2015 ◽

2015 ◽

Vol 15 (8) ◽

pp. 12353-12387 ◽

Cited By ~ 1

Author(s):

T. Schieferdecker ◽

S. Lossow ◽

G. P. Stiller ◽

T. von Clarmann

Keyword(s):

Solar Cycle ◽

Water Vapour ◽

Solar Maximum ◽

Time Lag ◽

Latitude Range ◽

Tropical Tropopause ◽

Solar Signal ◽

Tropopause Temperature ◽

Stratospheric Water Vapour ◽

Linear Trends

Abstract. A merged time series of stratospheric water vapour built from HALOE and MIPAS data between 60° S and 60° N and 15 to 30 km and covering the years 1992 to 2012 was analyzed by multivariate linear regression including an 11 year solar cycle proxy. Lower stratospheric water vapour was found to reveal a phase-shifted anti-correlation with the solar cycle, with lowest water vapour after solar maximum. The phase shift is composed of an inherent constant time lag of about 2 years and a second component following the stratospheric age of air. The amplitudes of the water vapour response are largest close to the tropical tropopause (up to 0.35 ppmv) and decrease with altitude and latitude. Including the solar cycle proxy in the regression results in linear trends of water vapour being negative over the full altitude/latitude range, while without the solar proxy positive water wapour trends in the lowermost stratosphere were found. We conclude from these results that a solar signal generated at the tropical tropopause is imprinted on the stratospheric water vapour abundances and transported to higher altitudes and latitudes via the Brewer–Dobson circulation. Hence it is concluded that the tropical tropopause temperature at the final dehydration point of air is also governed to some degree by the solar cycle. The negative water vapour trends obtained when considering the solar cycle impact on water vapour abundances can solve the water vapour conundrum of increasing stratospheric water vapour abundances at constant or even decreasing tropopause temperatures.

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