Changes In Water Vapor Content Research Articles

Large Ozone Hole in 2023 and the Hunga Tonga Volcanic Eruption

AbstractPolar stratospheric chemistry is highly sensitive to changes in water vapor content and temperature. We identified an unusual behavior of water vapor and temperature in the southern polar winter stratosphere in 2023. The relationships between the Hunga-Tonga eruption injection of water vapor (detected in the tropics) and its transport to SH high latitudes, temperature changes and ozone anomalies at southern high latitudes are discussed, as well as the roles of zonal wind and the meridional flux of zonal mean zonal momentum. These parameters exhibit a consistent pattern in anomalous year 2023. In the winter of 2023 in the Southern Hemisphere, an unexpected decrease in ozone levels and the emergence of an excessive ozone hole were observed. This event marked one of the deepest Antarctic ozone holes with the largest area since 2011. This appears to be associated with the Hunga Tonga eruption anomalous water vapor injection. This study highlights importance of water vapor for evolution of the Antarctic stratosphere.

A primary generalized empirical model of BVOC emissions for some typical forests in China

Measurements of emissions of biogenic volatile organic compounds (BVOCs), solar global radiation, photosynthetically active radiation and meteorological parameters were carried out in a subtropical Pinus plantation, China during 2013–2016. The results were used to further develop and evaluate an empirical model of BVOC emissions (EMBE). Simulated BVOC emissions are in good agreement with observations with relative biases of 32.8% and 2.6%, and normalized mean square error values of 0.092 and 0.001, for isoprene and monoterpene fluxes, respectively. Validation of the BVOC empirical model for half-hourly, hourly and mean hourly emission variations show that most BVOC emission patterns are reproduced. The validation of EMBE using gradient (GRA) measurements shows relative bias of 45.7% for isoprene and 76.9% for monoterpenes. Sensitivity tests show that BVOC emissions were more sensitive to changes in PAR than to changes in water vapor content or to the scattering factor. Using the EMBE model, average hourly and annual emissions were 0.59 and 2333.1 mg m−2 for isoprene and 0.79 and 2625.9 mg m−2 for monoterpenes during 2013–2016. Decreasing trends of isoprene and monoterpene emissions were observed in 2013–2016. EMBE estimated BVOC emissions were compared with estimates using the MEGAN model and measured fluxes. MEGAN estimated annual emissions by 2.5 times higher for isoprene, and a factor of 2 lower for monoterpenes than those estimated using EMBE over 2013–2016. Finally, a generalized EMBE model covering different conditions for three typical forests in China was presented and evaluated for better understanding BVOC emissions.

Assessing Rapid Variability in Atmospheric Apparent Optical Depth with an Array Spectrometer System

A method for determining rapid variations in atmospheric optical depth is proposed. The method is based upon computation of the ratio between close-time spectral measurements of solar direct flux. Use of the ratio avoids the need for absolute calibration of the instruments and minimizes the effects of changes in instrumental conditions (such as temperature or mechanical adjustments) and in air mass. The technique has been applied to some campaigns of measurement for sky conditions ranging from clear skies to scattered-to-broken cloudiness, performed at high frequency (~1Hz) with a system of three array spectrometers, capable of performing very rapid spectral acquisitions, in the 400 to 1700 nm band, thus covering the visible and extending to the near-infrared spectral ranges. Results demonstrate the capacity of this instrumentation and method to detect rapid variation of optical depth, as well as rapid changes in its spectral pattern. The optical depth variability depends on the particular state of the sky and is connected to particle condensation and evaporation processes and to the changes in water vapor content in the transition region between cloud-free and cloudy regions. Thus, the method is suitable for analyzing rapid processes involving particles, either aerosol or cloud droplets, and water vapor, in the cloud boundaries.

Changes in magnitude and frequency of heavy precipitation across China and its potential links to summer temperature

Changes in the magnitude, frequency and timing of heavy precipitation are closely related to the occurrence of floods and droughts, which hold a great deal of significance for management of agricultural irrigation and water resources. Records of daily precipitation and temperature from 728 stations across China were used to assess changes in the magnitude, frequency and timing of heavy precipitation using the Peak-over-Threshold (POT) with 95th percentile as the threshold. Because of the continuous nature of the magnitude and timing of heavy precipitation, the “change point” method and the modified Mann-Kendall trend test method were used to detect change points (CPs) and slowly-varying changes, respectively. In addition, the segmented regression and Poisson regression methods were used to detect CPs and temporal trends in the frequency of heavy precipitation, respectively, with consideration of the count nature of the data. The results showed that 55% and 36% of the stations had CPs in mean and/or variance of the magnitude and timing, respectively, while the percentage is only 5.8% in the frequency. However, while there is limited evidence of significant trends in the magnitude and timing, strong evidence points to a significant increasing frequency in most regions of China. These changes may be partly explained by changes in summer temperature. Examination of the summer surface temperature records suggests that the areas, where the frequency of heavy precipitation has a significant increase, are also mostly characterized by significant increasing temperature. In addition, trends of the frequency vary between the periods before and after the turn point (TP) of summer temperature trends, especially in northern China where both the summer temperature and the frequency have shifted significantly decreasing trends to significantly increasing trends. A possible interpretation of these findings is that storms tend to be more frequent without significant changes in water vapor content.

Trajectory of the Arctic as an integrated system

Although much remains to be learned about the Arctic and its component processes, many of the most urgent scientific, engineering, and social questions can only be approached through a broader system perspective. Here, we address interactions between components of the Arctic system and assess feedbacks and the extent to which feedbacks (1) are now underway in the Arctic and (2) will shape the future trajectory of the Arctic system. We examine interdependent connections among atmospheric processes, oceanic processes, sea-ice dynamics, marine and terrestrial ecosystems, land surface stocks of carbon and water, glaciers and ice caps, and the Greenland ice sheet. Our emphasis on the interactions between components, both historical and anticipated, is targeted on the feedbacks, pathways, and processes that link these different components of the Arctic system. We present evidence that the physical components of the Arctic climate system are currently in extreme states, and that there is no indication that the system will deviate from this anomalous trajectory in the foreseeable future. The feedback for which the evidence of ongoing changes is most compelling is the surface albedo-temperature feedback, which is amplifying temperature changes over land (primarily in spring) and ocean (primarily in autumn-winter). Other feedbacks likely to emerge are those in which key processes include surface fluxes of trace gases, changes in the distribution of vegetation, changes in surface soil moisture, changes in atmospheric water vapor arising from higher temperatures and greater areas of open ocean, impacts of Arctic freshwater fluxes on the meridional overturning circulation of the ocean, and changes in Arctic clouds resulting from changes in water vapor content.

Trajectory of the Arctic as an integrated system1

Although much remains to be learned about the Arctic and its component processes, many of the most urgent scientific, engineering, and social questions can only be approached through a broader system perspective. Here, we address interactions between components of the Arctic system and assess feedbacks and the extent to which feedbacks (1) are now underway in the Arctic and (2) will shape the future trajectory of the Arctic system. We examine interdependent connections among atmospheric processes, oceanic processes, sea-ice dynamics, marine and terrestrial ecosystems, land surface stocks of carbon and water, glaciers and ice caps, and the Greenland ice sheet. Our emphasis on the interactions between components, both historical and anticipated, is targeted on the feedbacks, pathways, and processes that link these different components of the Arctic system. We present evidence that the physical components of the Arctic climate system are currently in extreme states, and that there is no indication that the system will deviate from this anomalous trajectory in the foreseeable future. The feedback for which the evidence of ongoing changes is most compelling is the surface albedo-temperature feedback, which is amplifying temperature changes over land (primarily in spring) and ocean (primarily in autumn-winter). Other feedbacks likely to emerge are those in which key processes include surface fluxes of trace gases, changes in the distribution of vegetation, changes in surface soil moisture, changes in atmospheric water vapor arising from higher temperatures and greater areas of open ocean, impacts of Arctic freshwater fluxes on the meridional overturning circulation of the ocean, and changes in Arctic clouds resulting from changes in water vapor content.

Land surface emissivity retrieval from combined mid-infrared and thermal infrared data of MSG-SEVIRI

This work addressed the retrieval of Land Surface Emissivity (LSE) from combined mid-infrared and thermal infrared data of Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) onboard the geostationary satellite—Meteosat Second Generation (MSG). To correct for the atmospheric effects in satellite measurements, a new atmospheric correction scheme was developed for both Middle Infra-Red (MIR) and Thermal Infra-Red (TIR) channels. For the MIR channel, because it is less sensitive to the change of water vapor content, the clear-sky and time-nearest European Centre for Median-range Weather Forecast (ECMWF) atmospheric data were used for the images where no atmospheric data are available. For TIR channels, a modified model of Diurnal Temperature Cycle (DTC) used by Göttsche and Olesen [Göttsche, F. M., and Olesen, F. S. (2001). Modeling of diurnal cycles of brightness temperature extracted from METEOSAT data. Remote Sensing of Environment, 76, 337–348.] and Schädlich et al. [Schädlich, S., Göttsche, F. M., and Olesen, F. S. (2001). Influence of land surface parameters and atmosphere on METEOSAT brightness Temperatures and generation of land surface temperature maps by temporally and spatially interpolating atmospheric correction. Remote Sensing of Environment, 75, 39–46.] was adopted. The separation of Land Surface Temperature (LST) and LSE is based on the concept of the Temperature Independent Spectral Indices (TISI) [Becker, F., and Li, Z. L. (1990a). Temperature independent spectral indices in thermal infrared bands. Remote Sensing of Environment, 32, 17–33.] constructed with one channel in MIR and one channel in TIR. The results of two different combinations (combination of channels 4 and 9 and of channels 4 and 10) and two successive days at six specific locations over North Africa show that the retrievals are consistent. The range of emissivity in MSG-SEVIRI channel 4 goes from 0.5 for bare areas to 0.96 for densely vegetated areas, whereas the emissivities in MSG-SEVIRI channels 9 and 10 are usually from 0.9 to 0.95 for bare areas and from 0.95 to 1.0 for vegetated areas. For densely vegetated areas, the emissivities in MSG-SEVIRI channel 9 are larger than the ones in channel 10, whereas the opposite is observed over bare areas. The rms differences between two combinations over the whole studied region are 0.017 for emissivity in channel 4, 0.008 for emissivity in channel 9 and 0.007 for emissivity in channel 10.

Observed Interannual Variability of Tropical Troposphere Relative Humidity

Abstract Relative humidity fields from the High-Resolution Infrared Radiation Sounder (HIRS) flown on NOAA series satellites since 1979 have been used to study the seasonal aspects of the interannual variability of relative humidity in the tropical troposphere. The El Nino–Southern Oscillation (ENSO) is the only statistically identifiable physical mechanism of such variability. Boreal winter (December–February) relative humidity variations during an ENSO event follow patterns of anomalous convection and large-scale upper-level circulation. During El Nino (La Nina) regions of large negative (positive) relative humidity anomalies exist at subtropical latitudes over the Pacific Ocean. These are not always balanced by increases (decreases) in humidity near the equator. NCEP– NCAR reanalysis temperatures are used to separate observed changes in relative humidity into contributions from tropospheric temperature versus the contribution from changes in water vapor content. The authors find that at subtropical lat...

Aerosol properties in a Chinese semiarid region

Abstract Aerosol optical properties and atmospheric water vapor content for 1999–2000 were obtained from ground-based solar radiometer measurements in Dunhuang, China. Seasonal changes of aerosol optical depth (AOD) and Angstrom wavelength parameter (ALPHA) were observed. Large values of AOD (at 500 nm) greater than 1.0 combined with low values of ALPHA less than 0.2 were mainly observed in spring and summer, which is consistent with the seasonal dust production from Gobi and Taklamaken deserts. The maximum monthly average of AOD was around 0.37 and occurred in the April of 1999, which was more than three times larger than the minimum monthly average in the November of 2000 (around 0.115). Thirty-three percent and 49% of observations of AOD in autumn and winter was larger than 0.2, respectively, whereas in spring, the percentage was approximately 63%. There was a large spread in ALPHAs in all seasons when AODs were less than 0.2. With the increase of AOD, ALPHAs decreased rapidly and were around zero finally. The large spread of ALPHA for low AODs and the domination of low turbidity in Dunhuang (nearly half of AODs less than 0.2) resulted in the negligible seasonal change of ALPHA. The domination of coarse particles over fine particles was also shown in aerosol size distribution retrievals, with the volume concentration ratio of coarse to fine particles being nearly 30. The volume mean radii and standard deviation of size distribution showed an insignificant correlation with AOD based on the analysis of all available retrievals, illustrating that it is suitable to use a fixed size model in the analysis of the dust climate forcing. During the dust outbreak episode, a rapid increase of AOD and a decrease of ALPHA were observed, ALPHA being usually less than 0.2 and even negative occasionally. The interesting result was that the volume mean radii of size distribution during the dust outbreak episode increased remarkably with the dust loading, which indicated that a dynamic size model should be used in the simulation of dust effects on meso-scale weather system in the semiarid region. The distinct seasonal change of water vapor content was observed, with high water vapor contents occurred in summer. The influence of water vapor on aerosol properties was absent due to the low humidification capability of dust aerosols and the different seasonal variation of aerosol properties and water vapor content.

Relationship between sea surface temperature, vertical dynamics, and the vertical distribution of atmospheric water vapor inferred from TOVS observations

With the aim of better understanding the respective role of sea surface temperature (SST) and vertical dynamics on the vertical distribution of atmospheric water vapor, particularly in the tropics, global scale observations from NOAA 10, covering a 31−month period, have been processed using the improved initialization inversion ((3I) [Chédin and Scott, 1984]) retrieval method and interpreted in terms of tropospheric layered water vapor contents. The method of analysis uses the power law, which expresses the specific humidity q at pressure p as a function of their values at the surface, q0 and p0; q = q0(p/p0)λ. This description is applied independently to three layers giving three values of λ: λ1 for surface‐700 hPa, λ2 for 700–500 hPa, and λ3 for 500–300 hPa. It is shown that λ2 is a good indicator of the large‐scale vertical dynamics and gives results equivalent to those obtained using the vertical velocity at 500 hPa issued from a model. Consequently, the role of enhanced upward motion with increased SST for the “super greenhouse effect” situations is confirmed as well as the contribution of externally forced subsidence on the suppression of the deep convection for cases where SSTs exceed about 303 K. In addition, the influence of SST on the vertical distribution of water vapor is analyzed together with the large‐scale vertical dynamics contribution. The results show that the rate of change of water vapor content in the 700‐ to 500‐hPa and 500‐ to 300‐hPa layers with respect to SST increases with decreasing rate of change of λ2 with respect to SST, that is, with increasing rate of change of upward vertical dynamics with respect to SST.

Dehydration in the antarctic stratosphere: Radiative effects

A two dimensional model is used to investigate the effects of polar stratospheric clouds on the water vapor budget in the Antarctic stratosphere. It is shown that loss of stratospheric water vapor through formation and sedimentation of large ice particles decreases infrared cooling. This cooling reduction partially compensates the decreased ozone heating due to the formation of the Antarctic hole. Such a conclusion is reached by comparing a control unperturbed situation with two cases in which an ozone hole is formed with and without polar dehydration. We show that in the case of substantial loss of stratospheric water vapor since the years of the ozone hole formation, a dynamical mechanism may be necessary to explain the observed stratospheric cooling during the Antarctic spring. In this case the combined radiative perturbation (H2O + O3) is too small to force this cooling. Instead, in the case of a negligible change of water vapor content, the O3 radiative perturbation could be entirely responsible for the observed secular cooling.

On the estimation of surface radiation using satellite data

Model calculations are used to investigate the uncertainties in the surface radiative flux empirically derived from satellite radiation measurements and theoretically calculated from radiation models using satellite-inferred cloud parameters. The empirical approach depends upon how well the satellite-measured radiances (represented here by the top-of-the-atmosphere flux) correlate with the net flux at the surface. The model calculations show that while the TOA flux and the net surface flux are correlated with respect to changes in optical thickness, they are not correlated with respect to changes in cloud height and negatively correlated with respect to changes in water vapor content. It is also found that the solar zenith angle has a strong effect on these relationships. It is, therefore, important to correct for the effects of atmospheric water vapor content and the solar zenith angle in the empirical estimation of surface radiative flux. The theoretical approach depends upon the net effect of the uncertainty in satellite-inferred cloud parameters. In the solar spectral region, the effects of the uncertainty in satellite retrieval of could cover and optical thickness on the net downward surface flux are systematically in opposite directions, so that the combined effects is typically small (< 7 Wm−2). In the thermal infrared region, an error of 7 Wm−2 could be induced by an uncertainty of 100 mb in the cloud-base height or an uncertainty of 0.1 in the fractional cloud cover. As opposed to what is commonly perceived, the error in the surface flux is likely to be larger in the IR region than in the solar spectral region.

Global fluctuations in the distribution of atmospheric mass

Two global data sets have been analyzed to determine the interannual variability of the zonal mean mass distribution. The first is a National Meteorological Center (NMC) global data set of sea level pressures beginning in December 1977 and surface pressures beginning in April 1979. The second is an 11‐year (1972–1982) hybrid set of sea level pressures from the Australian southern hemisphere and U.S. Navy northern hemisphere analyses. The two sets are compared and evaluated by seeing how well they satisfy the constraint of conservation of mass. Anomalies in total mass due to changes in water vapor content of the atmosphere are lost in the data problems. Several inhomogeneities or discontinuities are found and are identified either with changes in analysis procedures in both data sets or the introduction of new orography and operational models at NMC. Consequently only limited periods of data are suitable for determining the dominant modes of variability. Nevertheless, hemispheric mean anomalies in mass in one hemisphere tend to be mirrored in the other, and it is clear that previously deduced fluctuations in hemispheric mean mass are mostly real. Predominant modes of variability of zonal means reveal systematic exchanges of mass (1) almost entirely confined within each hemisphere in isolation, (2) between the extratropics of each hemisphere with little impact on the tropics as an antisymmetric mode, and (3) between the tropics and extratropics in a symmetric mode. The second mode played a strong role in redistributing mass during April–July of 1979 during the First GARP Global Experiment (FGGE) and resulted in an exceptionally deep circumpolar trough over the southern hemisphere and record high pressures over the northern hemisphere. The possible origin of these modes is briefly considered.

Variations in air viscosity due to changes in water vapor pressure for isothermal conditions at temperatures below 40 °C

The viscosities of moist and dry air were measured at four temperatures to determine variations due to changes in water vapor content under isothermal test conditions. Paired measurements (240) of volumetric rates of air flow and pressure drops along a tube were made. Corresponding coefficients of viscosity were calculated from the Hagen–Poiseuille equation, laminar flow being assured by limiting maximal Reynolds numbers. The relationship between viscosity (η) and water vapor pressure [Formula: see text] was found to be approximately linear. The increase in the work load of the respiratory muscles due to an increase in air humidity, and hence viscosity, from purely physical considerations, appears to be very small compared with the total work of breathing.