Process-evaluation of tropospheric humidity simulated by general circulation models using water vapor isotopologues: 1. Comparison between models and observations

in Journal of Geophysical Research (2012), 117(D5), 05303

N2 - The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in ... [more ▼]

N2 - The goal of this study is to determine how H2O and HDO measurements in water vapor can be used to detect and diagnose biases in the representation of processes controlling tropospheric humidity in atmospheric general circulation models (GCMs). We analyze a large number of isotopic data sets (four satellite, sixteen ground-based remote-sensing, five surface in situ and three aircraft data sets) that are sensitive to different altitudes throughout the free troposphere. Despite significant differences between data sets, we identify some observed HDO/H2O characteristics that are robust across data sets and that can be used to evaluate models. We evaluate the isotopic GCM LMDZ, accounting for the effects of spatiotemporal sampling and instrument sensitivity. We find that LMDZ reproduces the spatial patterns in the lower and mid troposphere remarkably well. However, it underestimates the amplitude of seasonal variations in isotopic composition at all levels in the subtropics and in midlatitudes, and this bias is consistent across all data sets. LMDZ also underestimates the observed meridional isotopic gradient and the contrast between dry and convective tropical regions compared to satellite data sets. Comparison with six other isotope-enabled GCMs from the SWING2 project shows that biases exhibited by LMDZ are common to all models. The SWING2 GCMs show a very large spread in isotopic behavior that is not obviously related to that of humidity, suggesting water vapor isotopic measurements could be used to expose model shortcomings. In a companion paper, the isotopic differences between models are interpreted in terms of biases in the representation of processes controlling humidity. [less ▲]

Recent Behavior of the North Anatolian Fault: Insights from an Integrated Paleoseismological Dataset

in Journal of Geophysical Research (2010), 115(B09316),

The North Anatolian Fault (NAF) is a right‐lateral plate boundary fault that arcs across northern Turkey for ∼1500 km. Almost the entire fault progressively ruptured in the 20th century, its cascading ... [more ▼]

The North Anatolian Fault (NAF) is a right‐lateral plate boundary fault that arcs across northern Turkey for ∼1500 km. Almost the entire fault progressively ruptured in the 20th century, its cascading style indicating that stress from one fault rupture triggers fault rupture of adjacent segments. Using published paleoseismic investigations, this study integrates all of the existing information about the timing of paleoearthquakes on the NAF. Paleoseismic investigation data are compiled into a database, and for each site a Bayesian, ordering‐constrained age model is constructed in a consistent framework. Spatial variability of recurrence intervals suggests a spatial pattern in the behavior of earthquakes on the NAF that may correspond to the tectonic provinces within the Anatolian plate. In the west, the shear stress associated with the escaping Anatolian plate interplays with the tensile stress associated with the Aegean extensional province. Along this western transtensional section we recognize short recurrence intervals and switching between the furcated fault strands. The central section of the NAF is translational with little influence of fault‐normal stresses from other tectonic sources. This section tends to rupture in unison or close succession. The eastern section of the NAF is transpressional due to the compressional fault‐normal stress associated with the indenting Arabian plate. Along this section the recurrence intervals are bimodal, which we attribute to variable normal stress, although there are other possible causes. [less ▲]

Contributions of the driven process and the loading-unloading process during substorms: A study based on the IMAGE-SI12 imager

in Journal of Geophysical Research (2009), 114

Substorm energetics has been shown to have two components, the "loading-unloading'' component releasing energy previously stored in the tail and the "directly driven'' component dissipating simultaneously ... [more ▼]

Substorm energetics has been shown to have two components, the "loading-unloading'' component releasing energy previously stored in the tail and the "directly driven'' component dissipating simultaneously fed solar wind energy. Previous studies disagree about the relative importance of each process. The SI12 spectral imager onboard the IMAGE satellite provides images of the Doppler-shifted Lyman alpha auroral emission at 121.8 nm every 2 min. It has been used to determine the auroral intensity during substorms, which may be compared to the solar wind characteristics and interplanetary magnetic field components before and/or after substorm onsets. In this study, we analyze 256 substorms between June 2000 and December 2002, which satisfy criteria relative to the viewing conditions. We compare the mean nightside intensity during the expansion phase with the magnetic open flux, the epsilon parameter, and other coupling functions (used as proxies of transfer of solar wind energy to the magnetosphere) integrated over the growth phase or the expansion phase. The mean auroral intensity during the expansion phase correlates well with coupling functions integrated over the growth phase. We also find that the correlation between the auroral precipitation during the expansion phase and the coupling functions integrated over the expansion phase is lower but still significant. This implies that, even though both mechanisms contribute to the energy precipitated during substorms, the loading-unloading process is statistically dominant. [less ▲]

Seasonal, Kp, solar wind, and solar flux variations in long-term singlepass satellite estimates of electron and ion auroral hemispheric power

in Journal of Geophysical Research (2008), 113(A6),

Electron auroral energy flux is characterized by electron hemispheric power (Hpe) estimated since 1978 from National Oceanic and Atmospheric Administration (NOAA) and Defense Meteorological Satellite ... [more ▼]

Electron auroral energy flux is characterized by electron hemispheric power (Hpe) estimated since 1978 from National Oceanic and Atmospheric Administration (NOAA) and Defense Meteorological Satellite Program (DMSP) satellites after the estimates were corrected for instrumental problems and adjusted to a common baseline. Similarly, intersatellite adjusted ion hemispheric power (Hpi) estimates come from one MetOp and four NOAA satellites beginning in 1998. The hemispheric power (Hp) estimates are very crude, coming from single satellite passes referenced to 10 global activity levels, where the Hpi estimates are the difference between the total and the electron Hp (Hpi = Hpt-Hpe). However, hourly averaged NOAA/DMSP Hpe and Hpi estimates correlate well with hourly Polar Ultraviolet Imager (UVI) Hpt and Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) far ultraviolet (FUV) Hpe and Hpi estimates. Hpe winter values were larger than summer values similar to 65% of the time (when geomagnetic activity was moderate or higher), and Hpe were larger in the summer similar to 35% of the time (typically for low geomagnetic activity). Hpe was similar to 40% larger at winter solstice than summer solstice for the largest Hp from mostly nightside increases, and Hpe was similar to 35% larger in summer than winter for the smallest Hp owing to dayside auroral enhancements. Ion precipitation differed from electron precipitation because it was almost always larger in summer than winter. Hpe and Hpi increased with Kp, solar wind speed (Vsw), and negative Interplanetary Magnetic Field (IMF) B-z, similar to previous studies. Hpi also increased strongly with positive Bz. For quiet conditions, Hpe increased with increasing 10.7-cm solar flux (Sa), while Hpi increased with Sa up to Sa similar to 115 for all conditions. [less ▲]

Jupiter's changing auroral location

in Journal of Geophysical Research (2008), 113(A1),

[1] We examine the case of significant latitudinal shifts of the Jovian northern auroral emissions appearing in a data set spanning nine years of observations with the Hubble Space Telescope in the far ... [more ▼]

[1] We examine the case of significant latitudinal shifts of the Jovian northern auroral emissions appearing in a data set spanning nine years of observations with the Hubble Space Telescope in the far ultraviolet. The extended data set makes it possible to compare the location of the main auroral emission with similar viewing geometries and satellite positions. The main auroral emission is assumed to originate from beyond the orbit of Ganymede (15 Jovian radii). At these distances, near corotation enforcement and transfer of momentum from Jupiter to the magnetospheric plasma is ensured by means of field aligned currents. The field aligned currents away from Jupiter are carried by downward energetic electrons loosing their energy to the polar atmosphere and giving rise to the main auroral emission. Analysis of the polar projected images shows that the latitudinal location of the main emission has changed by up to 3 degrees over long periods of time. It also shows that the footprint of Ganymede follows a similar trend. We have used the VIP4 magnetic field model to map the emission down to the equatorial plane. This mapping suggests that internal variations of the current sheet parameters might be used as an alternative or complementary explanation to the changing solar wind conditions at Jupiter to explain the observed shift of auroral latitudes. [less ▲]

Auroral evidence of a localized magnetic anomaly in Jupiter's northern hemisphere

in Journal of Geophysical Research (2008), 113(A9),

We analyze more than 1000 HST/Advanced Camera for Survey images of the ultraviolet auroral emissions appearing in the northern hemisphere of Jupiter. The auroral footprints of Io, Europa, and Ganymede ... [more ▼]

We analyze more than 1000 HST/Advanced Camera for Survey images of the ultraviolet auroral emissions appearing in the northern hemisphere of Jupiter. The auroral footprints of Io, Europa, and Ganymede form individual footpaths, which are fitted with three reference contours. The satellite footprints provide a convenient mapping between the northern Jovian ionosphere and the equatorial plane in the middle magnetosphere, independent of any magnetic field model. The VIP4 magnetic field model is in relatively good agreement with the observed footprint of Io. However, in the auroral kink sector, between the 80 degrees and 150 degrees System III meridians, the model significantly departs from the observation. One possible way to improve the agreement between the VIP4 model and the observed footprints is to include a magnetic anomaly. We suggest that this anomaly is characterized by a weakening of the surface magnetic field in the kink sector and by an added localized tilted dipole field. This dipole rotates with the planet at a depth of 0.245 R-J below the surface, and its magnitude is set to similar to 1% of Jupiter's dipole moment. The anomaly has a very limited influence on the magnetic field intensity in the equatorial plane between the orbits of Io and Ganymede. However, it is sufficient to bend the field lines near the high-latitude atmosphere and to reproduce the observed satellite ultraviolet footpaths. JUNO's in situ measurements will determine the structure of Jupiter's magnetic field in detail to expand on these results. [less ▲]

Global morphology of substorm growth phases observed by the IMAGE-SI12 imager

in Journal of Geophysical Research (2007), 112(A11),

We present case studies and a statistical summary of optical observations of proton precipitation made during substorm growth phases. Our analysis is based on observations of the Doppler-shifted Lyman ... [more ▼]

We present case studies and a statistical summary of optical observations of proton precipitation made during substorm growth phases. Our analysis is based on observations of the Doppler-shifted Lyman-alpha auroral emission obtained with the SI12 Spectrographic Imager on board the IMAGE satellite. These images are used to determine the morphology and dynamics of the auroral oval and of the polar cap boundary on a global scale, as well as the total open magnetic flux and its time evolution. We also investigate the relationship with the solar wind and the interplanetary magnetic field ( IMF) characteristics measured by the ACE satellite and with the magnetic elevation angle measured by GOES-8. The statistical study shows that the sector of maximum proton precipitation during the growth phase is on average centered around 2200 MLT and rapidly shifts in local time by about 1.2 h toward midnight at the time of the onset. The open magnetic flux increases by 33% on average during the growth phase. The mean value of the open flux immediately before the substorm onset is about 0.66 GWb for substorms triggered by a northward turning of B-z and 0.74 GWb for nontriggered substorms. The averaged open flux at the substorm onset is smallest when the substorm is triggered by a sudden reversal of B-z, suggesting that the accumulation of energy by the magnetosphere is perturbed by changes in B-z. The open magnetic flux continues to increase during the 20 min following the onset, for a large number of events. The rate of equatorward displacement of the auroral oval boundaries during growth phase is typically similar to 3 deg/h. It is statistically correlated (r=0.40) with the magnitude of the Bz component of the IMF measured by the ACE satellite. It is also correlated, with higher coefficient (r=0.54), with functions describing the efficiency of solar wind energy transfer involving the transverse electric field carried by the solar wind. The equatorward motion may be global, restricted to local time sectors or a combination of both. At no nightside local time sector does the motion of the equatorial boundary appear more pronounced than at others, but the maximum displacement of the polar boundary is statistically located around midnight MLT. [less ▲]

A global inventory of stratospheric fluorine in 2004 based on Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) measurements

in Journal of Geophysical Research (2006), 111

Total fluorine (FTOT) in the stratosphere has been determined using Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) measurements of HF, COF2, COClF, CF4, CCl3F (CFC-11), CCl2F2 ... [more ▼]

Total fluorine (FTOT) in the stratosphere has been determined using Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) measurements of HF, COF2, COClF, CF4, CCl3F (CFC-11), CCl2F2 (CFC-12), CHClF2 (HCFC-22), CCl2FCClF2 (CFC-113), CH3CClF2 (HCFC-142b), CH2FCF3 (HFC-134a), and SF6. The retrieval of HFC-134a (CH2FCF3) from spaceborne measurements had not been carried out prior to this work. Measurements of these species have been supplemented by data from models to extend the altitude range of the profiles and have also been complemented by estimates of 15 minor fluorine species. Using these data, separate fluorine budgets were determined in five latitude zones (60°–82°N, 30°–60°N, 30°S–30°N, 30°–60°S, and 60°–82°S) by averaging over the period of February 2004 to January 2005 inclusive, when possible. Stratospheric FTOT profiles in each latitude zone are nearly linear, with mean stratospheric FTOT values ranging from 2.50 to 2.59 ppbv (with a 1sig precision of 0.04–0.07 ppbv and an estimated accuracy of 0.15 ppbv) for each zone. The highest mean FTOT value occurred in the tropics, which is qualitatively consistent with increasing levels of stratospheric fluorine and the mean stratospheric circulation pattern. [less ▲]

Irregular earthquake cycle along the southern Tianshan front, China (Aksu area)

in Journal of Geophysical Research (2005), 110(10.1029/2003JB002603),

A long deformation record (􏰩16.5 ka) showing nonsteady earthquake recurrence is established for the Aksu thrust (Tianshan, China) on the basis of cosmogenic 10Be dating of faulted surfaces. Topographic ... [more ▼]

A long deformation record (􏰩16.5 ka) showing nonsteady earthquake recurrence is established for the Aksu thrust (Tianshan, China) on the basis of cosmogenic 10Be dating of faulted surfaces. Topographic leveling across the Aksu fault scarp indicates up to 􏰩10 m uplift across a moraine abandoned 􏰩16.5 ka and similar uplift of 􏰩6 m across two inset surfaces yielding ages of 􏰩12.5 and 􏰩5 ka. Successively smaller uplifts of terraces younger than 5 ka indicate that three or more major earthquakes occurred during this period. These data show that the Aksu thrust fault was quiet for at least 7500 years and active in the last 􏰩5000 years and probably in the interval 16.5–12.5 ka. The seismic cycle along the Aksu thrust fault over the last 􏰩16,500 years was thus strongly irregular showing long quiescence and clustering, which is a challenge for paleoseismology and hazard assessment. This irregularity also makes it more difficult to estimate long-term shortening rates. Nevertheless, we are able to constrain a minimum total shortening rate (>7 mm/yr) across the southern Tianshan front for the last 12,500 years that is about a third of the total geodetic rate for the western Tianshan (􏰩20 mm/yr). [less ▲]

Distribution of surface carbon dioxide and air-sea exchange in the English Channel and adjacent areas

in Journal of Geophysical Research (2003), 108(C5),

In the present paper we report the distribution of the partial pressure of CO2 (pCO2) in surface waters along 13 transects in the English Channel, covering the four seasons. The spatial and temporal ... [more ▼]

In the present paper we report the distribution of the partial pressure of CO2 (pCO2) in surface waters along 13 transects in the English Channel, covering the four seasons. The spatial and temporal variability of pCO2 is controlled by a complex combination of primary production (from May to June), degradation of organic matter, temperature change, and freshwater inputs. Preliminary air-sea CO2 exchange computations suggest that the Channel is not a major sink of atmospheric CO2 and is probably neutral from the point of view of atmospheric coupling. This is mainly related to a relatively low export and/or burial of organic carbon and intense benthic calcification. [less ▲]