Inversion Depth Research Articles

Coupling an Advanced Land Surface–Hydrology Model with the Penn State–NCAR MM5 Modeling System. Part II: Preliminary Model Validation

A number of short-term numerical experiments conducted by the Penn State‐NCAR fifth-generation Mesoscale Model (MM5) coupled with an advanced land surface model, alongside the simulations coupled with a simple slab model, are verified with observations. For clear sky day cases, the MM5 model gives reasonable estimates of radiation forcing at the surface with solar radiation being slightly overestimated probably due to the lack of aerosol treatment in the current MM5 radiation scheme. The improvements in the calculation of surface latent and sensible heat fluxes with the new land surface model (LSM) are very apparent, and more importantly, the new LSM captures the correct Bowen ratio. Evaporation obtained from the simple slab model is significantly lower than observations. Having time-varying soil moisture is important for capturing even short-term evolution of evaporation. Due to the more reasonable diurnal cycle of surface heat fluxes in the MM5‐LSM, its nearsurface temperature and humidity are closer to the FIFE observations. In particular, the MM5‐slab model has a systematic warm bias in 2-m temperature. Both the slab model and the new LSM were coupled with the nonlocal Medium-Range Forecast model PBL parameterization scheme and they reproduced the depth of the morning surface inversion in the stable boundary layer well. The observed mixed layer in the late morning deepens faster than both models, despite the fact that both models have high bias in surface sensible heat fluxes. Presumably, such a rapid development of convective mixed layer is due to some effects induced by small-scale heterogeneity or large-scale advection that the MM5 failed to capture. Both surface models reasonably reproduce the daytime convective PBL growth and, in general, the temperature difference between the two models and observations is less than 28. The simulations of two rainfall events are not conclusive. Both models produce a good forecast of rainfall for 24 June 1997 and have similar problems for the event of 4 July 1997, although the simulations with the new LSM have slightly improved results in some 3-h rainfall accumulations. It seems that the new LSM does not have unexpected influences in situations for which the land surface processes are secondary, but that it may have subtle, though complex, effects on the model behavior because of heterogeneity introduced by soil moisture, vegetation effects, and soil type, which are all lacking in the slab model.

A simple thermodynamical model to estimate the rate of depletion of nocturnal low level inversion layer

The low level inversion, be it that of ground based or elevated, plays a significant role in the dispersion of polluted particles and in aviation meteorology. The rate of rise of the ground based inversion top and the base of elevated inversion causes the decrease of inversion strength and thereby permits vertical mixing of pollutants as the stability of the atmosphere is reduced. A simple thermodynamical model using the global radiation and vertical temperature profile has been proposed to estimate the rate of rise of (i) the ground based inversion top and (ii) the base of the elevated inversion. The depth of inversion thus estimated can be used in the pollution/fog dispersion models. The model is simple and operationally practicable. The limitations of the model are also discussed.

Decadal time scale trends and variability in the tropospheric circulation over the South Pole

This paper documents significant long‐term changes in the tropospheric circulation and progression of the seasonal cycle over the South Pole and relates aspects of the changes to the enhanced springtime stratospheric ozone depletion of recent decades. During the winter‐to‐summer transition over Antarctica, the formation of the thermal tropopause above 150 hPa is now delayed by a month compared to the early 1960s. A similar delay occurs in the breakdown of the winter polar stratospheric vortex, a prerequisite to the formation of the strong summertime tropopause near 300 hPa. A delay in tropopause formation implies delays in those aspects of the transition from winter to summer in the dynamics of the troposphere that are sensitive to its upper boundary condition, including the contraction of the Rossby radius of deformation during the shallow troposphere phase of summer. Consistent with this expectation, the normal springtime decline of baroclinic‐eddy activity in the lower troposphere now occurs later by a month. Similar delays occur in the time of an early summer minimum in total cloud fraction that coincides with the time of the maximum stratification between 150 and 100 hPa. In addition, the analyses reveal (1) an increase of 15 to 20% in spring and summer cloud fraction over the last four decades; (2) a separation of spring and summer cloudiness into two transport regimes with a distinct intervening minimum in cloud fraction; (3) a decadal modulation of springtime cloudiness that is coincident with decadal shifts in the directional mode of 300‐hPa winds following solar minima; (4) a long‐term increase in total inversion strength, inversion depth, and 650‐ to 300‐hPa thickness; and (5) a long‐term decrease in wintertime surface wind speed, surface temperature, and near‐surface lapse rate. The study also introduces a covariance technique that exploits the control by continental‐scale orography of synoptic and surface flow regimes, increasing the value of lower tropospheric observations for the study of climate change over Antarctica. Finally, a cautionary note arises from the apparent effect of the Weddell Polynyas and the reduction of the maximum extent of sea ice of the middle to late 1970s, with increased tropospheric and lower stratospheric temperatures and an earlier time of formation of the tropopause. This observation suggests that the occurrence of decadal and subdecadal variability in the ocean and the atmosphere of the Southern Hemisphere may obscure the detection of long‐term trends in the circulation over Antarctica.

Wintertime Evolution of the Temperature Inversion in the Colorado Plateau Basin

The Colorado Plateau, surrounded by a ring of mountains, has the meteorological characteristics of a basin. Deep, persistent potential temperature inversions form in this basin in winter. The formation, maintenance, and dissipation of these inversions are investigated using two to four times daily radiosonde data from the winter and early spring of 1989‐90. In winter, inversion evolution is forced primarily by synoptic-scale events. The buildup takes place over one or more days as warm air advection occurs above the basin with the approach of high pressure ridges. The breakup, which occurs with cold air advection above the basin as troughs approach, can occur over periods less than 12 h. Many approaching troughs modulate inversion strength and depth but are too weak to destroy the persistent inversion. Later in the winter and spring, the radiation-induced nocturnal inversion is destroyed nearly every day by the daytime growth of convective boundary layers from the basin floor and sidewalls.

The Temporal Behavior of the Atmospheric Boundary Layer in Israel

Upper-air measurements collected for three consecutive years (1987‐89) from the Israel Meteorological Service permanent sounding site, in Beit-Dagan, Israel, enabled the temporal behavior of the atmospheric boundary layer over Israel to be characterized. Data analyzed consisted of the layer depth, the thermal gradient within the layer, and occurrence frequency of radiative and elevated inversions. To adequately represent the multiyear seasonal and diurnal behavior, the 3-yr databases were merged based on the tested hypothesis that the month sample in each individual year comes from the same population. The analysis shows that the depth of the radiative ground-based inversion, its frequency, as well as its thermal profile are maximal during spring and early summer. The upper-inversion layer is well defined during the summer, its lowest base (0.5‐1 km MSL) indicating a sharp interface layer formed between the marine turbulent boundary layer at the shallow layer of the atmosphere and the subsiding downward motion caused by the subtropical high pressure system. During the other three seasons a significant temporal variation of the upper-inversion base is observed as a result of the frequent larger-scale synoptic weather systems. The diurnal variation of the mixed-layer depth is most evident during the summer because it is mainly governed by heat fluxes and the daily sea-breeze cycle that are most intensive then. Henceforth, the layer minimal depth, along the coast, usually occurs during late afternoon hours when the wind speed of the cool sea breeze reaches its minimal rate and heat fluxes dissipate rapidly, leading to a decrease of the marine turbulent boundary layer.

Second harmonic generation in a domain-inverted MgO-doped LiNbO3 waveguide by using a polarization axis inclined substrate

We demonstrate quasiphase matched second harmonic generation by use of annealed proton-exchanged 87° Z-cut MgO 5 mol % doped LiNbO3 (MgO:LN) waveguides supporting a TE-mode guided wave. Formation of a domain inversion was achieved by applying electric fields in 3° Y-cut and 87° Z-cut MgO:LN. In 3° Y-cut and 87° Z-cut MgO:LN substrates, a polarization axis inclines at an angle θ equal to 3° to the surface. The domain inversion was formed in a direction parallel to the polarization axis like needles stuck into the substrate. The depth of the domain inversion was 2.5 μm with a period of 4.75 μm. The depth was about 2.5 times deeper than that in X- and Y-cut substrate at an angle θ equal to 0°. By forming a waveguide on the domain-inverted substrate, a blue light of wavelength 475 nm, and a power of 37 mW has been obtained and a normalized second harmonic conversion efficiency was 300%/W cm2 with interaction length of 10 mm, using a tunable external cavity laser diode as a fundamental wave source.

Elevational changes in meteorological variables along a midlatitude glacier during summer

During the summer of 1994 a glaciometeorological experiment was carried out on the Pasterze (a glacier in Austria). This paper reports on the data from six energy‐balance stations ranging in altitude from 2075 to 3225 m above sea level (asl). The wind regime was dominated by the glacier wind. On the tongue, directional constancies ranged between 0.94 and 0.97. Mean 2 m wind speed and specifie humidity were almost constant along the glacier. The variation in the 2 m temperature along the glacier cannot be described by the usually assumed constant decrease with elevation. On the tongue the 2 m temperature even increased with elevation. A much better description of the temperature distribution is given by a linear relation between the potential temperature and the distance along the flow line. This can be understood from a simple thermodynamic analysis of the glacier‐wind layer. It is further shown that changes in clear‐sky global radiation with elevation are due mainly to changes in local albedo and relief and hardly at all to changes in absolute optical path length and atmospheric water vapor and aerosol content. On the tongue the laterally averaged ice albedo is almost constant with elevation. The flux of incoming long‐wave radiation during clear‐sky conditions at U2 (2310 m asl) was 48 W/m2 higher than the flux at U5 (3225 m asl), on average. More than half of the difference was due to systematic differences in the shape of the temperature profile (probably the inversion depth is larger at U2). The rest can be ascribed to higher 2 m temperatures and larger amounts of upper hemisphere slopes at U2. The distributions of the meteorological variables and the parameterizations described in this paper might be incorporated in surface energy‐balance models designed to simulate the surface mass balance.

“Morning-Glory” Disturbances and the Environment in which They Propagate

Results of a field experiment carried out in 1991 to gather upper-air data on the morning-glory environment are presented. The data include daily early morning radiosonde soundings from Burketown in north Queensland, Australia, for a 28-day period during the late dry season, together with pressure, wind, temperature, and humidity data from a number of surface stations in the region. During the experiment, 16 morning glories were recorded. On all but one day, radiosonde soundings were carried out in the pre-morning-glory environment. On 7 days, additional soundings were carried out within an hour or two of the passage of a morning glory. Soundings made on days on which morning glories were generated over Cape York Peninsula but failed to reach Burketown are compared with those on days when morning glories were recorded at Burketown. The comparison shows that the depth and strength of the surface-based inversion did not differ significantly and that the stratification of the almost neutral layer above the stable layer was similar on days with and without morning glories. An examination of the wind profiles is unrevealing and leads the authors to reject the hypothesis that the trapping of wave energy is the key factor that determines the longevity of the disturbances. That the leakiness of the wave-guide is not the only factor in the ability of disturbances to cover large distances from their place of origin is consistent with a numerical study by Noonan and Smith, which suggests that the morning-glory bore-wave system is formed and maintained by mesoscale circulations associated with the sea breezes over Cape York Peninsula.

Annealing Effects on Second Harmonic Generation of Segmented KTiOPO4 Waveguides

Annealing effects on second harmonic generation of a segmented KTiOPO4 waveguide fabricated by ion-exchange of Rb/Ba for K have been studied. Conversion efficiency was not affected by annealing at 250° C for 20 min but was greatly reduced by annealing at 400° C for 20 min. The results of selective etching by KOH/KNO3 showed that domain inversion of an ion-exchanged region remained even after annealing at 400° C. The lower conversion efficiency of the sample annealed at 400° C can be partly explained in terms of the lower power density of the fundamental beam and a relatively shallower depth of domain inversion than that of the waveguide due to the deepening of the waveguide caused by the diffusion of Rb and Ba inside the KTiOPO4 crystal.

Enhancement of domain inversion in LiTaO 3 using heat treatment with metal-oxide mask

The domain inversion depth is enhanced in proton-exchanged LiTaO/sub 3/ using heat treatment with a metal-oxide mask. Since this method can lower the proton exchange rate to get the same domain inversion depth, the degradation of the crystal quality in the domain-inverted layer is reduced. >

Large differences in Ti thermal diffusion caused domain inversion between undoped and MgO-doped LiNbO3

The periodic modulation of domain polarizations by Ti thermal diffusion on the +c face of LiNbO3 with and without MgO doping was studied systematically. It was shown that the depth of the inverted domain is quite different for these two substrates. Under the same fabrication conditions, the depth of domain inversion in the MgO-doped substrate is less than one-tenth that of the undoped substrate. This large difference can be explained by the presence of MgO in LiNbO3, which decreases the Ti diffusion constant and increases the minimum Ti concentration required for domain inversion.

A numerical study of boundary-layer dynamics in a mountain valley

The characteristics of dynamics and thermodynamics of the atmospheric boundary layer in a part of the Colorado River Valley, centered around Lake Mohave, have been investigated by analysis of measurements conducted during a field program in late spring and early summer of 1986 and a series of numerical simulations by a three-dimensional second-moment turbulence-closure model. The model was validated against measurements described in a companion article (Enger et al., 1993). According to airsonde measurements performed on eight nights, the depth of the surface inversion was around 200 m with an average temperature gradient of about 30 K km −1 . Analysis of acoustic sounder data collected during one month revealed significant diurnal variations of U and V wind-speed components related to slope and valley flows, respectively

Domain inversion in MgO-diffused LiNbO_3

We obtain the periodic modulation of domain polarization by patterning MgO on the positive C-face of LiNbO(3), followed by Li outdiffusion to induce domain inversion. We obtain domain inversion lines (1.5 microm) by heat treating LiNbO(3) at 1000 degrees C for 2 h with a 1-microm inversion depth. This process may be suitable for fabrication of first-order gratings that are needed for high second-harmonic conversion efficiency by using a quasi-phase-matched technique.

Tropospheric low‐level temperature inversions in the Canadian Arctic

Abstract Climatological characteristics of the low‐level tropospheric temperature inversion in the Canadian Arctic are examined using 10–40 year records of upper‐air meteorological data. Inversions at the northern sites are primarily surface‐based in winter, and elevated from mid‐spring through summer. At the southern sites, a bimodal pattern is observed with surface‐based inversions occurring during late summer, as well as during winter. From comparisons of our results with other published climatologies, it appears that this bimodal pattern reflects interactions between short‐ and long‐wave radiation, synoptic activity and snowmelt. Maxima in inversion depth and temperature difference across the inversion layer occur in February and March; minima occur in August and September. The annual progression of inversion characteristics closely follows the annual pattern of clear‐sky percentages, reflecting the controlling influence of cloud and clear‐sky radiative forcings on the inversion layer.

Low-Level Temperature Inversions of the Eurasian Arctic and Comparisons with Soviet Drifting Station Data

Seasonal and regional variations in characteristics of the Arctic low-level temperature inversion are examined using up to 12 years of twice-daily rawinsonde data from 31 inland and coastal sites of the Eurasian Arctic and a total of nearly six station years of data from three Soviet drifting stations near the North Pole. The frequency of inversions, the median inversion depth, and the temperature difference across the inversion layer increase from the Norwegian Sea eastward toward the Laptev and East Siberian seas. This effect is most pronounced in winter and autumn, and reflects proximity to oceanic influences and synoptic activity, possibly enhanced by a gradient in cloud cover. East of Novaya Zemlya during winter, inversions are found in over 95% of all soundings and tend to be surface based. For all locations, however, inversions tend to he most intense during winter due to the large deficit in surface net radiation. The strongest inversions are found over eastern Siberia, and reflect the effects of local topography. The frequency of inversions is lowest during summer, but is still >50% at all locations. Most summer inversions are elevated, and are much weaker than their winter counterparts. Data from the drifting stations reveal an inversion in every sounding from December to April. The minimum frequency of 85% occurs during August. While the median inversion depth is over 1200 m during March, it decreases to approximately 400 m during August, with median temperature differences across the inversion layer of 12.6° and 2.8°C, respectively. The median depth of the summertime mixed layer below inversions at the drifting stations ranges from 300 to 400 m. Seasonal changes in these inversion characteristics show a strong relationship with seasonal changes in cloud cover.

The development and structure of nocturnal slope winds in a simple valley

The results of an observational and modeling study of the nocturnal slope winds in a simple valley are presented. The valley was approximately 225 m deep in the region of the measurements, and featured a uniform slope angle of approximately 23 ° on one of its sidewalls. The wind and temperature structure of the katabatic flows on the valley sidewalls were measured with tower-mounted instruments, and a Doppler sodar and instruments on a tethered balloon and a 61-m tower were used to determine the atmospheric conditions near the center of the valley. The temperature structure of the slope flows was summarized by characteristic scale parameters h and δT for the inversion depth and strength, respectively. On the sidewalls 50 m above the valley floor, the inversion depths were generally smaller and the inversion strengths were weaker than they were on the sidewalls 100 m higher. These results differ significantly from those obtained over a simple slope of an isolated mountain or ridge. The down-valley winds are shown to be important in limiting the strength of the sidewall inversions. The formation of an inversion in the valley also has a pronounced effect on the structure of the slope flows. Numerical simulations suggest that the presence of adiabatic layers in the valley atmosphere is associated with decreases in the slope-flow inversion depth with increasing downslope distance. The simulations also indicate that the length scales that characterize the momentum and inversion depths behave similarly in flows down simple slopes but not in flows down the sidewalls of a valley.

Characteristics of the low‐level temperature inversion along the Alaskan Arctic coast

AbstractThe climatological characteristics of low‐level tropospheric temperature inversion along the Alaskan Arctic coast are examined from a 10‐year record of surface and upper‐air meteorological data at Barrow and Barter Island, Alaska. The meteorology at the two stations is found to be remarkably similar; surface‐based inversions occur nearly half of the time, but even in the winter months inversions are frequently based up to 200 m above the surface. Median inversion depths range from 250m to 850m, with median temperature differences across the inversion ranging from 2°C to 11°C. In March and April when the inversion is strongest, the lowest levels frequently erode. This indicates that the transient character of the inversion reduces its effectiveness as a barrier to vertical mixing. The inversion depth closely follows the annual cloud‐cover cycle, demonstrating that the development and maintenance of the inversion is a result of complex interactions between radiative forcing, synoptic activity, and sea‐ice dynamics.

Determination of the seabed porosity and shear modulus profiles using a gravity wave inversion : Geophys JV98, N1, July 1989, P173–182

SUMMARY A previously developed Bottom Shear Modulus Profiler (BSMP) theory (Yamamoto & Torii 1986) allows the seabed shear modulus versus depth profile to be extracted by inverting measurements of seabed motion and water wave-induced pressures at one point on the seafloor. Preliminary BSMP experiments (Trevorrow et af. 1988b; Badiey et af. 1988), compared to existing geologic borehold data at two inner continental shelf sites, showed that this method can accurately predict the magnitude and depth structure of the sediment shear modulus. An improved version of BSMP instrumentation system has been developed and deployed in deeper water at outer continental shelf sites. Gravity water wave-induced bottom pressures are measured in a period band from 7 to 200s, whereas measurements of gravity water wave-induced ground motion are limited to a period band between 7 and 30 s, due to the limited sensitivity of the seismometers used. It is also found that burial of a BSMP in the seabed improved the seabed seismometer coupling significantly. The BSMP inversions of these data extract the shear modulus versus depth profile of the seabed with a depth resolution of a few meters and penetrating as much as 200m into the seabed. The shear modulus of a sediment at a given depth of burial is a unique function of the porosity of the sediment. Using this relation, the porosity versus depth profile of the seabed is calculated from the shear modulus profile obtained by the BSMP inversion. Excellent agreements are shown between the porosity profiles obtained from the BSMP inversion and the borehole porosity logs. The pressure data indicate that the potential penetration depth of the BSMP inversion is about 2 km into the continental shelf and 20 km into the deep seafloor.

Determination of the seabed porosity and shear modulus profiles using a gravity wave inversion

SUMMARY A previously developed Bottom Shear Modulus Profiler (BSMP) theory (Yamamoto & Torii 1986) allows the seabed shear modulus versus depth profile to be extracted by inverting measurements of seabed motion and water wave-induced pressures at one point on the seafloor. Preliminary BSMP experiments (Trevorrow et af. 1988b; Badiey et af. 1988), compared to existing geologic borehold data at two inner continental shelf sites, showed that this method can accurately predict the magnitude and depth structure of the sediment shear modulus. An improved version of BSMP instrumentation system has been developed and deployed in deeper water at outer continental shelf sites. Gravity water wave-induced bottom pressures are measured in a period band from 7 to 200s, whereas measurements of gravity water wave-induced ground motion are limited to a period band between 7 and 30 s, due to the limited sensitivity of the seismometers used. It is also found that burial of a BSMP in the seabed improved the seabed seismometer coupling significantly. The BSMP inversions of these data extract the shear modulus versus depth profile of the seabed with a depth resolution of a few meters and penetrating as much as 200m into the seabed. The shear modulus of a sediment at a given depth of burial is a unique function of the porosity of the sediment. Using this relation, the porosity versus depth profile of the seabed is calculated from the shear modulus profile obtained by the BSMP inversion. Excellent agreements are shown between the porosity profiles obtained from the BSMP inversion and the borehole porosity logs. The pressure data indicate that the potential penetration depth of the BSMP inversion is about 2 km into the continental shelf and 20 km into the deep seafloor.

Prestack migration by shot record inversion and common depth point stacking: a case study

In this paper a method for depth migration of individual shot records followed by common depth point (CDP) stacking is described and iIIustrated with a real data example. First we explain the philosophy behind shot record migration. Then we go through the different stages of the procedure using a real data example.