scholarly journals Tropospheric methane in the tropics – first year from IASI hyperspectral infrared observations

2009 ◽  
Vol 9 (17) ◽  
pp. 6337-6350 ◽  
Author(s):  
C. Crevoisier ◽  
D. Nobileau ◽  
A. M. Fiore ◽  
R. Armante ◽  
A. Chédin ◽  
...  
Keyword(s):  
Seasonal Cycle ◽  
Atmospheric Transport ◽  
Deep Convection ◽  
High Spectral Resolution ◽  
Boreal Winter ◽  
Monsoon Period ◽  
Transport Pathways ◽  
Geographical Patterns ◽  
Methane Distribution ◽  
The Tropics

Abstract. Simultaneous observations from the Infrared Atmospheric Sounding Interferometer (IASI) and from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the European MetOp platform in October 2006, are used to retrieve a mid-to-upper tropospheric content of methane (CH4) in clear-sky conditions, in the tropics, over sea, for the first 16 months of operation of MetOp (July 2007–October 2008). With its high spectral resolution, IASI provides nine channels in the 7.7 μm band highly sensitive to CH4 with reduced sensitivities to other atmospheric variables. These channels, sensitive to both CH4 and temperature, are used in conjunction with AMSU channels, only sensitive to temperature, to decorrelate both signals through a non-linear inference scheme based on neural networks. A key point of this approach is that no use is made of prior information in terms of methane seasonality, trend, or geographical patterns. The precision of the retrieval is estimated to be about 16 ppbv (~0.9%). Features of the retrieved methane space-time distribution include: (1) a strong seasonal cycle of 30 ppbv in the northern tropics with a maximum in January–March and a minimum in July–September, and a flat seasonal cycle in the southern tropics, in agreement with in-situ measurements; (2) a latitudinal decrease of 30 ppbv from 20° N to 20° S, in boreal spring and summer, lower than what is observed at the surface but in excellent agreement with tropospheric aircraft measurements; (3) geographical patterns in good agreement with simulations from the atmospheric transport and chemistry model MOZART-2, but with a higher variability and a higher concentration in boreal winter; (4) signatures of CH4 emissions transported to the middle troposphere such as a large plume of elevated tropospheric methane south of the Asian continent, which might be due to Asian emissions from rice paddies uplifted by deep convection during the monsoon period and then transported towards Indonesia. In addition to bringing a greatly improved view of methane distribution, these results from IASI should provide a means to observe and understand atmospheric transport pathways of methane from the surface to the upper troposphere.

scholarly journals A new insight on tropospheric methane in the Tropics – first year from IASI hyperspectral infrared observations

2009 ◽  
Vol 9 (2) ◽  
pp. 6855-6887 ◽  
Author(s):  
C. Crevoisier ◽  
D. Nobileau ◽  
A. M. Fiore ◽  
R. Armante ◽  
A. Chédin ◽  
...  
Keyword(s):  
Seasonal Cycle ◽  
Atmospheric Transport ◽  
Deep Convection ◽  
High Spectral Resolution ◽  
Boreal Winter ◽  
Monsoon Period ◽  
Transport Pathways ◽  
Geographical Patterns ◽  
Methane Distribution ◽  
The Tropics

Abstract. Simultaneous observations from the Infrared Atmospheric Sounding Interferometer (IASI) and from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the European MetOp platform in October 2006, are used to retrieve a mid-to-upper tropospheric content of methane (CH4) in clear-sky conditions, in the Tropics, over sea, for the first 16 months of operation of MetOp (July 2007–October 2008). With its very high spectral resolution, IASI provides nine channels in the 7.7 μm band highly sensitive to CH4 with reduced sensitivities to other atmospheric variables. These channels, sensitive to both CH4 and temperature, are used in conjunction with AMSU channels, only sensitive to temperature, to decorrelate both signals through a non-linear inference scheme based on neural networks. A key point of this approach is that no use is made of prior information in terms of methane seasonality, trend, or geographical patterns. The accuracy of the retrieval is estimated to be about 16 ppbv (~0.9%). Features of the retrieved methane space-time distribution include: (1) a strong seasonal cycle of 30 ppbv in the Northern Tropics with a maximum in January–March and a minimum in July–September, and a flat seasonal cycle in the Southern Tropics, in agreement with in-situ measurements; (2) a latitudinal decrease of 30 ppbv from 20° N to 20° S, in boreal spring and summer, lower than what is observed at the surface but in excellent agreement with tropospheric aircraft measurements; (3) geographical patterns in good agreement with simulations from the atmospheric transport and chemistry model MOZART-2, but with a higher variability and a higher concentration in boreal winter; (4) signatures of CH4 emissions transported to the middle troposphere such as a large plume of elevated tropospheric methane south of the Asian continent, which might be due to Asian emissions from rice paddies uplifted by deep convection during the monsoon period and then transported towards Indonesia. In addition to bringing a greatly improved view of methane distribution, these results from IASI should provide a means to observe and understand atmospheric transport pathways of methane from the surface to the upper troposphere.

scholarly journals First year of upper tropospheric integrated content of CO<sub>2</sub> from IASI hyperspectral infrared observations

2009 ◽  
Vol 9 (14) ◽  
pp. 4797-4810 ◽  
Author(s):  
C. Crevoisier ◽  
A. Chédin ◽  
H. Matsueda ◽  
T. Machida ◽  
R. Armante ◽  
...  
Keyword(s):  
Seasonal Cycle ◽  
Atmospheric Transport ◽  
Time Lag ◽  
High Spectral Resolution ◽  
First Year ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Geographical Patterns ◽  
Carbon Dioxide Co2 ◽  
June July

Abstract. Simultaneous observations from the Infrared Atmospheric Sounding Interferometer (IASI) and from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the European MetOp platform in October 2006, are used to retrieve an upper tropospheric content of carbon dioxide (CO2) covering the range 11–15 km (100–300 hPa), in clear-sky conditions, in the tropics, over sea, for the first year of operation of MetOp (January 2008–December 2008). With its very high spectral resolution, IASI provides fourteen channels in the 15 μm band highly sensitive to CO2 with reduced sensitivities to other atmospheric variables. IASI observations, sensitive to both CO2 and temperature, are used in conjunction with AMSU observations, only sensitive to temperature, to decorrelate both signals through a non-linear inference scheme based on neural networks. A key point of this approach is that no use is made of prior information in terms of CO2 seasonality, trend, or geographical patterns. The precision of the retrieval is estimated to be about 2.0 ppmv (~0.5%) for a 5°×5° spatial resolution on a monthly time scale. Features of the retrieved CO2 space-time distribution include: (1) a strong seasonal cycle of 4 ppmv in the northern tropics with a maximum in June–July and a minimum in September–October. This cycle is characterized by a backward two-months lag as compared to the surface, by a backward one-month lag as compared to measurements performed at 11 km, and by a forward one-month lag as compared to observations performed at the tropopause (16 km). This is likely due to the time-lag of CO2 cycle while transported from the surface to the upper troposphere; (2) a more complex seasonal cycle in the southern tropics, in agreement with in-situ measurements; (3) a latitudinal variation of CO2 shifting from a South-to-North increase of 3.5 ppmv in boreal spring to a South-to-North decrease of 1.5 ppmv in the fall, in excellent agreement with tropospheric aircraft measurements; (4) signatures of CO2 emissions transported to the upper troposphere. In addition to bringing an improved view of CO2 distribution, these results from IASI should provide an additional means to observe and understand atmospheric transport pathways of CO2 from the surface to the upper troposphere.

scholarly journals First year of upper tropospheric integrated content of CO<sub>2</sub> from IASI hyperspectral infrared observations

2009 ◽  
Vol 9 (2) ◽  
pp. 8187-8222 ◽  
Author(s):  
C. Crevoisier ◽  
A. Chédin ◽  
H. Matsueda ◽  
T. Machida ◽  
R. Armante ◽  
...  
Keyword(s):  
Seasonal Cycle ◽  
Atmospheric Transport ◽  
Time Lag ◽  
High Spectral Resolution ◽  
First Year ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Geographical Patterns ◽  
Carbon Dioxide Co2 ◽  
June July

Abstract. Simultaneous observations from the Infrared Atmospheric Sounding Interferometer (IASI) and from the Advanced Microwave Sounding Unit (AMSU), launched together onboard the European MetOp platform in October 2006, are used to retrieve an upper tropospheric content of carbon dioxide (CO2) covering the range 11–15 km (100–300 hPa), in clear-sky conditions, in the tropics, over sea, for the first year of operation of MetOp (January 2008–December 2008). With its very high spectral resolution, IASI provides fourteen channels in the 15 μm band highly sensitive to CO2 with reduced sensitivities to other atmospheric variables. IASI observations, sensitive to both CO2 and temperature, are used in conjunction with AMSU observations, only sensitive to temperature, to decorrelate both signals through a non-linear inference scheme based on neural networks. A key point of this approach is that no use is made of prior information in terms of CO2 seasonality, trend, or geographical patterns. The accuracy of the retrieval is estimated to be about 2.0 ppmv (~0.5%) for a 5°×5° spatial resolution on a monthly time scale. Features of the retrieved CO2 space-time distribution include: (1) a strong seasonal cycle of 4 ppmv in the northern tropics with a maximum in June–July and a minimum in September–October. This cycle is characterized by a backward two-months lag as compared to the surface, by a backward one-month lag as compared to measurements performed at 11 km, and by a forward one-month lag as compared to observations performed at the tropopause (16 km). This is likely due to the time-lag of CO2 cycle while transported from the surface to the upper troposphere; (2) a more complex seasonal cycle in the southern tropics, in agreement with in-situ measurements; (3) a latitudinal variation of CO2 shifting from a South-to-North increase of 3.5 ppmv in boreal spring to a South-to-North decrease of 1.5 ppmv in the fall, in excellent agreement with tropospheric aircraft measurements; (4) signatures of CO2 emissions (such as biomass burning) transported to the troposphere. In addition to bringing an improved view of CO2 distribution, these results from IASI should provide an additional means to observe and understand atmospheric transport pathways of CO2 from the surface to the upper troposphere.

scholarly journals Tropical convective transport and the Walker circulation

2012 ◽  
Vol 12 (5) ◽  
pp. 12229-12244 ◽  
Author(s):  
J. S. Hosking ◽  
M. R. Russo ◽  
P. Braesicke ◽  
J. A. Pyle
Keyword(s):  
Deep Convection ◽  
Walker Circulation ◽  
Convective Transport ◽  
Boreal Winter ◽  
Maritime Continent ◽  
Transport Pathways ◽  
East Pacific ◽  
Upward Transport ◽  
Fast Transport ◽  
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, preferred transport routes from the troposphere to the stratosphere are found in the model 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. At the same time, the downwelling branch of the Walker Circulation is enhanced over the East Pacific, compared to other months in 2005, reducing locally the upward transport from emissions below. We conclude that the Walker circulation plays an important role in the seasonality of fast tropical transport from the troposphere to the stratosphere and so impacts at the same time the potential supply of surface emissions.

scholarly journals Tropical convective transport and the Walker circulation

2012 ◽  
Vol 12 (20) ◽  
pp. 9791-9797 ◽  
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.

Tropical Cold-Point Tropopause: Climatology, Seasonal Cycle, and Intraseasonal Variability Derived from COSMIC GPS Radio Occultation Measurements

2012 ◽  
Vol 25 (15) ◽  
pp. 5343-5360 ◽  
Author(s):  
Joowan Kim ◽  
Seok-Woo Son
Keyword(s):  
Seasonal Cycle ◽  
Radio Occultation ◽  
Deep Convection ◽  
Intraseasonal Variability ◽  
Kelvin Waves ◽  
Boreal Summer ◽  
Boreal Winter ◽  
Frequency Spectra ◽  
Gps Radio Occultation ◽  
Cold Point

Abstract The finescale structure of the tropical cold-point tropopause (CPT) is examined using high-resolution temperature profiles derived from Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) global positioning system (GPS) radio occultation measurements for 4 yr from September 2006 to August 2010. The climatology, seasonal cycle, and intraseasonal variability are analyzed for three CPT properties: temperature (T-CPT), pressure (P-CPT), and sharpness (S-CPT). Their relationships with tropospheric and stratospheric processes are also discussed. The climatological P-CPT is largely homogeneous in the deep tropics, whereas T-CPT and S-CPT exhibit local minima and maxima, respectively, at the equator in the vicinity of deep convection regions. All three CPT properties, however, show coherent seasonal cycle in the tropics; the CPT is colder, higher (lower in pressure), and sharper during boreal winter than during boreal summer. This seasonality is consistent with the seasonal cycle of tropical upwelling, which is largely driven by stratospheric and near-tropopause processes, although the amplitude of the seasonal cycle of T-CPT and S-CPT is modulated by tropospheric circulations. On intraseasonal time scales, P-CPT and T-CPT exhibit homogeneous variability in the deep tropics, whereas S-CPT shows pronounced local variability and seasonality. The wavenumber–frequency spectra reveal that intraseasonal variability of CPT properties is primarily controlled by Kelvin waves, with a nonnegligible contribution by Madden–Julian oscillation convection. The Kelvin waves, which are excited by deep convection but often propagate along the equator freely, explain the homogeneous P-CPT and T-CPT variabilities. On the other hand, the vertically tilted dipole of temperature anomalies, which is associated with convectively coupled equatorial waves, determines the local structure and seasonality of S-CPT variability.

Human influence on the seasonal cycle of tropospheric temperature

Science ◽  
2018 ◽  
Vol 361 (6399) ◽  
pp. eaas8806 ◽  
Author(s):  
Benjamin D. Santer ◽  
Stephen Po-Chedley ◽  
Mark D. Zelinka ◽  
Ivana Cvijanovic ◽  
Céline Bonfils ◽  
...  
Keyword(s):  
Seasonal Cycle ◽  
Large Scale ◽  
Climate Models ◽  
Scientific Evidence ◽  
Tropospheric Temperature ◽  
Geographical Patterns ◽  
Physical Mechanisms ◽  
Statistical Confidence ◽  
Earth’S Climate ◽  
The Tropics

We provide scientific evidence that a human-caused signal in the seasonal cycle of tropospheric temperature has emerged from the background noise of natural variability. Satellite data and the anthropogenic “fingerprint” predicted by climate models show common large-scale changes in geographical patterns of seasonal cycle amplitude. These common features include increases in amplitude at mid-latitudes in both hemispheres, amplitude decreases at high latitudes in the Southern Hemisphere, and small changes in the tropics. Simple physical mechanisms explain these features. The model fingerprint of seasonal cycle changes is identifiable with high statistical confidence in five out of six satellite temperature datasets. Our results suggest that attribution studies with the changing seasonal cycle provide powerful evidence for a significant human effect on Earth’s climate.

scholarly journals Transport pathways from the Asian monsoon anticyclone to the stratosphere

2015 ◽  
Vol 15 (18) ◽  
pp. 25981-26023 ◽  
Author(s):  
H. Garny ◽  
W. J. Randel
Keyword(s):  
Large Scale ◽  
Asian Monsoon ◽  
Deep Convection ◽  
Three Dimensional ◽  
Reanalysis Data ◽  
Vertical Transport ◽  
Heating Rates ◽  
Transport Pathways ◽  
Northern Summer ◽  
The Tropics

Abstract. Transport pathways of air originating in the upper tropospheric Asian monsoon anticyclone are investigated based on three-dimensional trajectories. The Asian monsoon anticyclone emerges in response to persistent deep convection over India and southeast Asia in northern summer, and this convection is associated with rapid transport from the surface to the upper troposphere, and possibly into the stratosphere. Here, we investigate the fate of air that originates within the upper tropospheric anticyclone from the outflow of deep convection, using trajectories driven by ERA-interim reanalysis data. Calculations include isentropic estimates, plus fully three-dimensional results based on kinematic and diabatic transport calculations. Isentropic calculations show that air parcels are typically confined within the anticyclone for 10–20 days, and spread over the tropical belt within a month of their initialization. However, only few parcels (3 % at 360 K, 8 % at 380 K) reach the extratropical stratosphere by isentropic mixing. When considering vertical transport we find that 31 % (48%) of the trajectories reach the stratosphere within 60 days when using vertical velocities or diabatic heating rates to calculate vertical transport, respectively. In both cases, most parcels that reach the stratosphere are transported upward within the anticyclone and enter the stratosphere in the tropics, typically 10–20 days after their initialization at 360 K. This suggests that trace gases, including pollutants, that are transported into the stratosphere via the Asian monsoon system are in a position to enter the tropical pipe and thus be transported into the deep stratosphere. Sensitivity calculations with respect to the initial altitude of the trajectories showed that air needs to be transported to levels of 360 K or above by deep convection to likely (&amp;geqq;50 %) reach the stratosphere through transport by the large-scale circulation.

scholarly journals Geographic and seasonal distributions of CO transport pathways and their roles in determining CO centers in the upper troposphere

2012 ◽  
Vol 12 (10) ◽  
pp. 4683-4698 ◽  
Author(s):  
L. Huang ◽  
R. Fu ◽  
J. H. Jiang ◽  
J. S. Wright ◽  
M. Luo
Keyword(s):  
Central Africa ◽  
Lower Troposphere ◽  
Convective Transport ◽  
Boreal Winter ◽  
Transport Pathway ◽  
Austral Spring ◽  
Transport Pathways ◽  
Upper Troposphere ◽  
Joint Application ◽  
The Tropics

Abstract. Past studies have identified a variety of pathways by which carbon monoxide (CO) may be transported from the surface to the tropical upper troposphere (UT); however, the relative roles that these transport pathways play in determining the distribution and seasonality of CO in the tropical UT remain unclear. We have developed a method to automate the identification of two pathways ("local convection" and "advection within the lower troposphere (LT) followed by convective vertical transport") involved in CO transport from the surface to the UT. This method is based on the joint application of instantaneous along-track, co-located, A-Train satellite measurements. Using this method, we find that the locations and seasonality of the UT CO maxima in the tropics were strongly correlated with the frequency of local convective transport during 2007. We also find that the "local convection" pathway (convective transport that occurred within a fire region) typically transported significantly more CO to the UT than the "LT advection → convection" pathway (advection of CO within the LT from a fire region to a convective region prior to convective transport). To leading order, the seasonality of CO concentrations in the tropical UT reflected the seasonality of the "local convection" transport pathway during 2007. The UT CO maxima occurred over Central Africa during boreal spring and over South America during austral spring. Occurrence of the "local convection" transport pathway in these two regions also peaked during these seasons. During boreal winter and summer, surface CO emission and convection were located in opposite hemispheres, which limited the effectiveness of transport to the UT. During these seasons, CO transport from the surface to the UT typically occurred via the "LT advection → convection" pathway.

scholarly journals Seasonality of the Structure and Propagation Characteristics of the MJO

2016 ◽  
Vol 73 (9) ◽  
pp. 3511-3526 ◽  
Author(s):  
Ángel F. Adames ◽  
John M. Wallace ◽  
Joy M. Monteiro
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Deep Convection ◽  
Winter Season ◽  
Water Model ◽  
Boreal Winter ◽  
Northwest Pacific ◽  
Monsoon Period ◽  
Asian Summer ◽  
Frictional Convergence

Abstract The seasonality of the Madden–Julian oscillation (MJO) is documented in observational data, and a nonlinear shallow-water model is used to help interpret some of the contrasts in MJO structure between the boreal winter season [November–March (NDJFM)] and the Asian summer monsoon period [June–September (JJAS)]. At upper-tropospheric levels, the flanking Rossby waves remain centered around 28°N/S year-round, but they tend to be stronger in the winter hemisphere, where the climatological-mean jet stream is stronger, rendering the subtropical circulation more sensitive to forcing by a near-equatorial heat source. Amplitudes of the MJO-related deep convection and lower-tropospheric zonal wind are stronger in the summer hemisphere, where the column-integrated water vapor is larger. During NDJFM, the equatorial asymmetry is subtle: as in the annual mean, moisture convergence into swallowtail-shaped regions of enhanced deep convection is an integral part of the equatorial Rossby wave signature, and the eastward propagation is due to moistening of the air to the east of the enhanced convection by poleward moisture advection. During the Asian summer monsoon in JJAS, the convection assumes the form of northward-propagating, west-northwest–east-southeast-oriented rainbands embedded within cyclonic shear lines. These features are maintained by frictional convergence of moisture, and their northward propagation is mainly due to the presence of features in the climatological-mean fields: that is, the west–east moisture gradient over India and the Arabian Sea and the southwesterly low-level monsoon flow over the northwest Pacific.

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