Water Vapor Abundance Research Articles

Water vapor toward starless cores: TheHerschelview

SWAS and Odin provided stringent upper limits on the gas phase water abundance of dark clouds (x(H2O) < 7x10^-9). We investigate the chemistry of water vapor in starless cores beyond the previous upper limits using the highly improved angular resolution and sensitivity of Herschel and measure the abundance of water vapor during evolutionary stages just preceding star formation. High spectral resolution observations of the fundamental ortho water (o-H2O) transition (557 GHz) were carried out with Herschel HIFI toward two starless cores: B68, a Bok globule, and L1544, a prestellar core embedded in the Taurus molecular cloud complex. The rms in the brightness temperature measured for the B68 and L1544 spectra is 2.0 and 2.2 mK, respectively, in a velocity bin of 0.59 km s^-1. The continuum level is 3.5+/-0.2 mK in B68 and 11.4+/-0.4 mK in L1544. No significant feature is detected in B68 and the 3 sigma upper limit is consistent with a column density of o-H2O N(o-H2O) < 2.5x10^13 cm^-2, or a fractional abundance x(o-H2O) < 1.3x10^-9, more than an order of magnitude lower than the SWAS upper limit on this source. The L1544 spectrum shows an absorption feature at a 5 sigma level from which we obtain the first value of the o-H2O column density ever measured in dark clouds: N(o-H2O) = (8+/-4)x10^12 cm^-2. The corresponding fractional abundance is x(o-H2O) ~ 5x10^-9 at radii > 7000 AU and ~2x10^-10 toward the center. The radiative transfer analysis shows that this is consistent with a x(o-H2O) profile peaking at ~10^-8, 0.1 pc away from the core center, where both freeze-out and photodissociation are negligible. Herschel has provided the first measurement of water vapor in dark regions. Prestellar cores such as L1544 (with their high central densities, strong continuum, and large envelopes) are very promising tools to finally shed light on the solid/vapor balance of water in molecular clouds.

Potential for stratospheric Doppler windspeed measurements of Jupiter by sub-millimetre spectroscopy

The sub-millimetre/microwave range of the spectrum has been exploited in the field of Earth observation by many instruments over the years and has provided a plethora of information on atmospheric chemistry and dynamics—however, this spectral range has not been fully explored in planetary science, having been exclusively employed to carry out ground-based measurements. To this end, a sub-millimetre instrument, the Orbiter Terahertz Infrared Spectrometer (ORTIS), is studied by the University of Oxford and the Rutherford Appleton Laboratory, to meet the requirements of the European Space Agency's Cosmic Visions 2015–2025 programme—in particular, the Europa Jupiter System Mission (EJSM), which has the European Space Agency and the National Aeronautics and Space Administration as partners. ORTIS is designed to measure atmospheric temperature, the abundance of stratospheric water vapour and other jovian gases, and is intended to be capable of retrieving vertical profiles of horizontal windspeed in the stratosphere for the first time, from Doppler-shifted emission lines measured at high spectral resolution. In this work, a preliminary study and implementation of the estimation of windspeed profiles on simulated spectra representative of Jupiter is presented, detailing the development of the retrieval algorithm, showing that a sub-millimetre instrument such as ORTIS should be able to retrieve windspeed profiles to an accuracy of about 15 m/s between 70 and 200 km/0.1–10 mb using a single near-limb measurement, for expected noise amplitudes.

Correlations between cloud thickness and sub‐cloud water abundance on Venus

Past spacecraft observations of Venus have found considerable spatial and temporal variations of water vapour abundance above the clouds. Previous searches for variability below the clouds at 30–45 km altitude found no large scale latitudinal gradients, but lacked the spatial resolution to detect smaller scale variations. Here we interpret results from the VIRTIS imaging spectrometer on Venus Express, remotely sounding at near‐infrared ‘spectral window’ wavelengths, as indicating that the water vapour abundance at 30–40 km altitude varies from 22 to 35 ppmv (±4 ppmv). Furthermore, this variability is correlated with cloud opacity, supporting the hypothesis that its genesis is linked to cloud convection. It is also possible to fit the observations without requiring spatial variation of water abundance, but this places a strong constraint on the spectral dependence of the refractive index data assumed for the lower cloud particles, for which there is as yet no supporting evidence.

Continuous photometric observations at ENEA base in Lampedusa to estimate precipitable water

Water vapour is a variable component of the atmosphere both in space and time. It is one of the most important components because of its effects in many fi elds: Meteorology, Climatology, Remote Sensing, Energy-Budget, Hydrology, etc. This work compares radiometric (sun photometer) readings, Global Positioning System (GPS) data and a meteorological model forecasted data. The aim is to understand if GPS measurements may help Numerical Weather Prediction (NWP) models. It is well known that GPS measurements are affected by the so-called tropospheric delay. Part of it, the so-called wet delay is related mainly to the amount of water vapour along the path of the GPS signal through the troposphere. Precise knowledge of the abundance of water vapour, in space and time, is important for NWP model because water vapour is the predecessor of precipitation. Despite the high variability of water vapour compared to other meteorological fi elds, like pressure and wind, water vapour observations are scarce, so that additional measurements of water vapour are expected to benefi t meteorology. A new sun photometer, which is part of the AERONET (AErosol and RObotic NETwork) program, has been installed at the ENEA (Ente per le Nuove tecnologie, l'Energia e l'Ambiente) base of Lampedusa Island. The sun photometer is quite close (less then 4 km) to an ASI (Agenzia Spaziale Italiana) GPS permanent receiver. A long record (summer period of the year 2000) of sun photometric measurements is available for the station at Lampedusa. We found that the GPS and sun photometric data are better correlated (std. dev. about 10 mm for the wet delay) than are the GPS measurements with the NWP model predictions. This is an indication that GPS delay data may contain information useful for weather prediction.

RADIATIVE TRANSFER MODELS OF MID-INFRARED H2O LINES IN THE PLANET-FORMING REGION OF CIRCUMSTELLAR DISKS

The study of warm molecular gas in the inner regions of protoplanetary disks is of key importance for the study of planet formation and especially for the transport of H2O and organic molecules to the surfaces of rocky planets/satellites. Recent Spitzer observations have shown that the mid-infrared spectra of protoplanetary disks are covered in emission lines due to water and other molecules. Here, we present a non-LTE 2D radiative transfer model of water lines in the 10-36 mum range that can be used to constrain the abundance structure of water vapor, given an observed spectrum, and show that an assumption of local thermodynamic equilibrium (LTE) does not accurately estimate the physical conditions of the water vapor emission zones. By applying the model to published Spitzer spectra we find that: 1) most water lines are subthermally excited, 2) the gas-to-dust ratio must be one to two orders of magnitude higher than the canonical interstellar medium ratio of 100-200, and 3) the gas temperature must be higher than the dust temperature, and 4) the water vapor abundance in the disk surface must be truncated beyond ~ 1 AU. A low efficiency of water formation below ~ 300 K may naturally result in a lower water abundance beyond a certain radius. However, we find that chemistry, may not be sufficient to produce an abundance drop of many orders of magnitude and speculate that the depletion may also be caused by vertical turbulent diffusion of water vapor from the superheated surface to regions below the snow line, where the water can freeze out and be transported to the midplane as part of the general dust settling. Such a vertical cold finger effect is likely to be efficient due to the lack of a replenishment mechanism of large, water-ice coated dust grains to the disk surface.

Water vapor variability in the north polar region of Mars from Viking MAWD and MGS TES datasets

Atmospheric water vapor abundances in Mars’ north polar region (NPR, from 60° to 90°N) are mapped as function of latitude and longitude for spring and summer seasons, and their spatial, seasonal, and interannual variability is discussed. Water vapor data are from Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and the Viking Orbiter (VO) Mars Atmospheric Water Detector (MAWD). The data cover three complete northern spring–summer seasons in 1977–1978, 2000–2001 and 2002–2003, and shorter periods of spring–summer seasons during 1975, 1999 and 2004. Long term interannual variability in the averaged NPR abundances may exist, with Viking MAWD observations showing twice as much water vapor during summer as the MGS TES observations more than 10 martian years (MY) later. While the averaged abundances are very similar in TES observations for the same season in different years, the spatial distributions in the early summer season do vary significantly year over year. Spatial and temporal variabilities increase between L s ∼ 80–140°, which may be related to vapor sublimation from the North Polar Residual Cap (NPRC), or to changes in circulation. Spatial variability is observed on scales of ∼100 km and temporal variability is observed on scales of <10 sols during summer. During late spring the TES water vapor spatial distribution is seen to correlate with the low topography/low albedo region of northern Acidalia Planitia (270–360°E), and with the dust spatial distribution across the NPR during late spring–early summer. Non-uniform vertical distribution of water vapor, a regolith source or atmospheric circulation ‘pooling’ of water vapor from the NPRC into the topographic depression may be behind the correlation with low topography/low albedo. Sublimation winds carrying water vapor off the NPRC and lifting surface dust in the areas surrounding the NPRC may explain the correlation between the water vapor and dust spatial distributions. Correlation between water vapor and dust in MAWD data are only observed over low topography/low albedo area. Maximum water vapor abundances are observed at L s = 105–115° and outside of the NPRC at 75–80°N; the TES data, however, do not extend over the NPRC and thus, this conclusion may be biased. Some water vapor appears to be released in plumes or ‘outbursts’ in the MAWD and TES datasets during late spring and early summer. We propose that the sublimation rate of ice varies across the NPRC with varying surface winds, giving rise to the observed ‘outbursts’ at some seasons.

Mapping of water frost and ice at low latitudes on Mars

This paper reports on mapping of water frost and ice on Mars, in the range of latitudes between 30°S and 30°N. The study has been carried out by analysing 2485 orbits acquired during almost one martian year by the Mars Express/OMEGA imaging spectrometer. Water frost/ice is identified by the presence of ∼1.5 μm, ∼2 μm and ∼3.0 μm absorptions. Although the orbits analysed in this study cover all seasons, water frost/ice is observed only near the aphelion seasons, at Ls = 19° and at Ls = 98–150°. Water frost/ice is detected mainly on the southern hemisphere between 15°S and 30°S latitude while it has not been identified within 15°S–15°N. In the northern hemisphere, the water frost/ice detection is complicated by the presence of clouds. Usually, water frost/ice is found in shadowed areas, while in few cases it is exposed to the sunlight. This indicates a clear relationship with the local illumination conditions on the slopes which favour the water frost/ice deposition on the surface when the temperatures are very low. OMEGA observations span from 10 to 17 LT and the frost/ice is detected mainly between 15 and 16 LT, with practically no detection before 13 LT. We think this is due to the fact that the 10–12 LT observations occur at large distances and it is not a local time effect. A thermal model is used to determine the deposition conditions on the sloped surfaces where water frost/ice has been found. There, daily atmospheric saturation does not occur on pole facing 10–25° slopes with current water vapour abundances but only by assuming values greater than 40 pr μm. Moreover, the water frost/ice is not detected during the northern winter, even if the thermal model foresees daily saturation on 25° slopes.

Pressure broadening coefficients of [formula omitted] induced by [formula omitted] for Venus atmosphere

Carbon dioxide ( CO 2 ) induced pressure broadening coefficients of water vapor ( H 2 O ) lines have been determined using a terahertz time-domain spectrometer (TDS). Thirty-two rotational transitions of H 2 O were observed in the spectral range of 18– 102 cm - 1 (550–3050 GHz) for the first time. Using TDS allows one to measure absorption spectra with one order of magnitude better precision than Fourier transform spectrometer in this frequency region. The precision of our broadening coefficient measurements was 2.4% in average. The measured CO 2 induced pressure broadening coefficients are compared to those calculated by the complex Robert–Bonamy formalism. The difference between the measurement and the theoretical estimation was in the range of - 10.7 % to + 19.0 % confirming the credibility of the theoretical approach. The impact on retrieval of water vapor abundance was examined by performing inversion analysis on H 2 O spectra of Venus atmosphere obtained with the Submillimeter Wave Astronomy Satellite. In this example case, the retrieved water vapor mixing ratio reduces by half at the altitude region of 70–85 km when applying the newly measured broadening coefficient compared to the air-broadening coefficient, and changes by 5% compared to that estimated by the complex Robert–Bonamy formalism.

Water vapor abundance near the surface of Venus from Venus Express/VIRTIS observations

Nightside observations of the 1.18‐μm atmospheric window by the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) aboard the Venus Express spacecraft were analyzed to measure and map the water vapor abundance in the lower atmosphere. Thermal emission in this window originates partly from the surface and partly from the first scale height (0–15 km) of the atmosphere. Constraints on the CO2 continuum absorption, which is the dominant source of gaseous opacity in the window, were obtained from the variation of the 1.185‐μm intensity with surface elevation. An absorption coefficient of 1 ± 0.4 × 10−9 cm−1 amagat−2 best fits the observed variation. We retrieved a water vapor mole fraction of 44 ± 9 ppm from various selections of VIRTIS spectra in the southern hemisphere, in agreement with previous analyses of the nightside emission. This value is somewhat larger than that previously determined at higher altitudes from the 2.3‐ and 1.74‐μm nightside windows, but the error bars still allow a constant with height H2O mole fraction from the surface up to 40 km. Using the intensity ratio in the two wings of the 1.18‐μm window as a proxy, we searched for horizontal variations of the H2O abundance in various VIRTIS observational sequences. We derived stringent upper limits for any possible latitudinal variations on the night side: ±1.5% in the range 60°S–25°N and ±3% for the broader range 80°S–25°N. The lack of detectable latitudinal variations is consistent with a constant with height water profile in the lower atmosphere and probably precludes any strong concentration gradient near the surface.

Analysis of thermal emission from the nightside of Venus at 1.51 and 1.55 μm

We present radiative transfer modelling of thermal emission from the nightside of Venus in two ‘spectral window’ regions at 1.51 and 1.55 μm. The first discovery of these windows, reported by Erard et al. [Erard, S., Drossart, P., Piccioni, G., 2009. J. Geophys. Res. Planets 114, doi:10.1029/2008JE003116. E00B27], was achieved using a principal component analysis of data from the VIRTIS instrument on Venus Express. These windows are spectrally narrow, with a full-width at half-maximum of ∼20 nm, and less bright than the well-known 1.7 and 2.3 μm spectral windows by two orders of magnitude. In this note we present the first radiative transfer analysis of these windows. We conclude that the radiation in these windows originates at an altitude of 20–35 km. As is the case for the other infrared window regions, the brightness of the windows is affected primarily by the optical depth of the overlying clouds; in addition, the 1.51 μm radiance shows a very weak sensitivity to water vapour abundance.

Compact Reconnaissance Imaging Spectrometer observations of water vapor and carbon monoxide

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard the Mars Reconnaissance Orbiter (MRO) spacecraft began taking observations in September 2006 and has now collected more than a full Martian year of data. Retrievals performed using the near‐infrared spectra obtained by CRISM are used to characterize the seasonal and spatial variation of the column abundance of water vapor and the column‐averaged mixing ratio of carbon monoxide. CRISM retrievals show nominal behavior in water vapor during northern hemisphere spring and summer with maximum abundance reaching 50 precipitable micrometers. Water vapor abundance during the southern hemisphere spring and summer appears significantly reduced compared to observations by other instruments taken during previous years. The CRISM retrievals show the seasonally and globally averaged carbon monoxide mixing ratio to be 700 ppm, but with strong seasonal variations at high latitudes. The summertime near‐polar carbon monoxide mixing ratio falls to 200 ppm in the south and 400 ppm in the north as carbon dioxide sublimates from the seasonal polar ice caps and dilutes noncondensable species including carbon monoxide. At low latitudes, the carbon monoxide mixing ratio varies in response to the mean seasonal cycle of surface pressure.

Strong water absorption in the dayside emission spectrum of the planet HD 189733b

Recent observations of the extrasolar planet HD 189733b did not reveal the presence of water in the emission spectrum of the planet. Yet models of such 'hot-Jupiter' planets predict an abundance of atmospheric water vapour. Validating and constraining these models is crucial to understanding the physics and chemistry of planetary atmospheres in extreme environments. Indications of the presence of water in the atmosphere of HD 189733b have recently been found in transmission spectra, where the planet's atmosphere selectively absorbs the light of the parent star, and in broadband photometry. Here we report the detection of strong water absorption in a high-signal-to-noise, mid-infrared emission spectrum of the planet itself. We find both a strong downturn in the flux ratio below 10 microm and discrete spectral features that are characteristic of strong absorption by water vapour. The differences between these and previous observations are significant and admit the possibility that predicted planetary-scale dynamical weather structures may alter the emission spectrum over time. Models that match the observed spectrum and the broadband photometry suggest that heat redistribution from the dayside to the nightside is weak. Reconciling this with the high nightside temperature will require a better understanding of atmospheric circulation or possible additional energy sources.

Tropical methane emissions: A revised view from SCIAMACHY onboard ENVISAT

Methane retrievals from near‐infrared spectra recorded by the SCIAMACHY instrument onboard ENVISAT hitherto suggested unexpectedly large tropical emissions. Even though recent studies confirm substantial tropical emissions, there were indications for an unresolved error in the satellite retrievals. Here we identify a retrieval error related to inaccuracies in water vapor spectroscopic parameters, causing a substantial overestimation of methane correlated with high water vapor abundances. We report on the overall implications of an update in water spectroscopy on methane retrievals with special focus on the tropics where the impact is largest. The new retrievals are applied in a four‐dimensional variational (4D‐VAR) data assimilation system to derive a first estimate of the impact on tropical CH4 sources. Compared to inversions based on previous SCIAMACHY retrievals, annual tropical emission estimates are reduced from 260 to about 201 Tg CH4 but still remain higher than previously anticipated.

MEDUSA: The ExoMars experiment for in-situ monitoring of dust and water vapour

Dust and water vapour are fundamental components of the Martian atmosphere. In view of tracing the past environmental conditions on Mars, that possibly favoured the appearing of life forms, it is important to study the present climate and its evolution. Here dust and water vapour have (and have had) strong influence. Of major scientific interest is the quantity and physical, chemical and electrical properties of dust and the abundance of water vapour dispersed in the atmosphere and their exchange with the surface. Moreover, in view of the exploration of the planet with automated systems and in the future by manned missions, it is of primary importance to analyse the hazards linked to these environmental factors. The Martian Environmental Dust Systematic Analyser (MEDUSA) experiment, included in the scientific payload of the ESA ExoMars mission, accommodates a complement of sensors, based on optical detection and cumulative mass deposition, that aims to study dust and water vapour in the lower Martian atmosphere. The goals are to study, for the first time, in-situ and quantitatively, physical properties of the airborne dust, including the cumulative dust mass flux, the dust deposition rate, the physical and electrification properties, the size distribution of sampled particles and the atmospheric water vapour abundance versus time.

A latitudinal survey of CO, OCS, H2O, and SO2 in the lower atmosphere of Venus: Spectroscopic studies using VIRTIS‐H

The high‐resolution channel (R ≃ 2000) of the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument (VIRTIS‐H) aboard Venus Express has provided numerous spectra of the nightside infrared thermal emission in the 2.3‐μm window. Mixing ratios of various minor species in the 30–40 km range could therefore be inferred using this spectral window at higher latitudes accessible to the spacecraft but which cannot be observed from Earth. The previously known enhancement in carbon monoxide (CO) toward high latitudes is confirmed and extended up to 60° with a mixing ratio varying from 24 ± 3 to 31 ± 2 ppmv at 36 km. Measurements of carbonyl sulfide (OCS) also agree with the previously suspected latitudinal variations that are anticorrelated with those of CO, ranging between 2.5 ± 1 and 4 ± 1 ppmv at 33 km. New constraints were also derived on the mean abundance of water vapor (H2O, 31 ± 2 ppmv) and sulfur dioxide (SO2, 130 ± 50 ppmv) in the probed altitude range. CO and OCS variations are interpreted as caused by large‐scale vertical motions, an explanation under current testing by various chemical and dynamical modeling. In such a case, these variations may help constrain the chemical time scale of those species in the lower troposphere.

A study of the Martian water vapor over Hellas using OMEGA and PFS aboard Mars Express

We used the OMEGA imaging spectrometer aboard Mars Express to study the evolution of the water vapor abundance over the Hellas basin, as a function of the seasonal cycle. The H 2 O column density is found to range from very low values (between southern fall and winter) up to more than 15 pr-μm during southern spring and summer. The general behavior is consistent with the expected seasonal cycle of water vapor on Mars, as previously observed by TES and modeled. In particular, the maximum water vapor content is observed around the southern solstice, and is significantly less than its northern couterpart. However, there is a noticeable discrepancy around the northern spring equinox (L s = 330-60°), where the observed H 2 O column densities are significantly lower than the values predicted by the GCM. Our data show an abrupt enhancement of the water vapor column density (from 3 to 16 pr-μm) on a timescale of 3 days, for L s = 251-254°. Such an increase, not predicted by the GCM, was also occasionally observed by TES over Hellas during previous martian years at the same season; however, its origin remains to be understood.

Organic Molecules and Water in the Planet Formation Region of Young Circumstellar Disks

The chemical composition of protoplanetary disks is expected to hold clues to the physical and chemical processes that influence the formation of planetary systems. However, characterizing the gas composition in the planet formation region of disks has been a challenge to date. We report here that the protoplanetary disk within 3 astronomical units of AA Tauri possesses a rich molecular emission spectrum in the mid-infrared, indicating a high abundance of simple organic molecules (HCN, C2H2, and CO2), water vapor, and OH. These results suggest that water is abundant throughout the inner disk and that the disk supports an active organic chemistry.

Simultaneous mapping of H 2O and H 2O 2 on Mars from infrared high-resolution imaging spectroscopy

New maps of martian water vapor and hydrogen peroxide have been obtained in November–December 2005, using the Texas Echelon Cross Echelle Spectrograph (TEXES) at the NASA Infra Red Telescope facility (IRTF) at Mauna Kea Observatory. The solar longitude L s was 332° (end of southern summer). Data have been obtained at 1235–1243 cm −1, with a spectral resolution of 0.016 cm −1 ( R = 8 × 10 4 ). The mean water vapor mixing ratio in the region [0°–55° S; 345°–45° W], at the evening limb, is 150 ± 50 ppm (corresponding to a column density of 8.3 ± 2.8 pr-μm ). The mean water vapor abundance derived from our measurements is in global overall agreement with the TES and Mars Express results, as well as the GCM models, however its spatial distribution looks different from the GCM predictions, with evidence for an enhancement at low latitudes toward the evening side. The inferred mean H 2O 2 abundance is 15 ± 10 ppb , which is significantly lower than the June 2003 result [Encrenaz, T., Bézard, B., Greathouse, T.K., Richter, M.J., Lacy, J.H., Atreya, S.K., Wong, A.S., Lebonnois, S., Lefèvre, F., Forget, F., 2004. Icarus 170, 424–429] and lower than expected from the photochemical models, taking in account the change in season. Its spatial distribution shows some similarities with the map predicted by the GCM but the discrepancy in the H 2O 2 abundance remains to be understood and modeled.

ＮＯＡＡ ＡＶＨＲＲを用いた日本の陸域可降水量分布図の作成

This paper proposes a method to estimate precipitable water (PW) distribution over land using NOAA Advanced Very High Resolution Radiometer (AVHRR) thermal data, and mapping of daily PW over Japan from 1984 to 2001 were carried out using this method. The method adopts the split-window algorithm which utilizes the differential atmospheric effect in the two thermal wavebands. The brightness temperature difference between AVHRR channel 4 and 5 (denoted as T4-T5) increases along with atmospheric water vapor abundance, scan angle and land surface temperature (LST) . The effect caused by scan angle and LST was simulated using radiative transfer model and the correction formulas to eliminate theses effects from (T4-T5) were developed. The PW estimation formula was derived from the regression analysis between the (T4-T5) and GPS-derived PW. The root-mean-square error of the PW estimation is approximately 6 mm, and our AVHRR-based estimation has a fairly good result compared with that of radiosondes.

Regulation of H2O and CO in tropical tropopause layer by the Madden‐Julian oscillation

Impacts of the Madden‐Julian oscillation (MJO) on the water vapor (H2O) and carbon monoxide (CO) abundances in the tropical tropopause layer (TTL) are investigated using Aura Microwave Limb Sounder (MLS) data for November 2004 to May 2005. The effects of the eastward propagation of MJO on H2O and CO abundances in the TTL are evident. Deep convection transports H2O into the upper troposphere up to about the 355‐ to 365‐K level. Around the 365‐ to 375‐K level, a dry anomaly is collocated with a cold anomaly, which is above a warm anomaly located near the region of convection enhancement. Tropical mean H2O at 375 K is regulated by the MJO through convection enhancement and is coherent with the local MJO‐related temperature variation. The locations of dehydration follow the eastward propagation of convection enhancement, and its area extent depends on the phase of the MJO. Enhancement of deep convection associated with the MJO also injects CO from the lower troposphere to the TTL up to 375 K. However, tropical mean CO at 375 K responds instantaneously to the large injection event occurring over the African continent.