Water Vapour Potential Vorticity and Its Applications in Tropical Cyclones

A new tracer is presented to diagnose tropical cyclones （TCs） and their correspondent rainfall. It is defined as water vapour potential vorticity （WPV） by replacing potential temperature with specific humidity in the potential vorticity （PV）. The WPV is compared with PV and moist potential vorticity （MPV） in diagnosing three tropical cyclone cases occurred in North-West Pacific during 10 July to 21 July 2005 （Haitang）, 30 July to 9 August 2005 （Matsa） and 25 September to 3 October 2005 （Longwang） separately. The results show that in tracing the track of TCs, WPV is not nicer than PV but better than MPV. While diagnosing TCs＇ onshore rainfall, WPV is better than MPV in all the three cases. Moreover, the advection of WPV is a good indication of TC rainfall after its landing.     

Global Structures and Multi-Temporal Variabilities of MLT Migrating Diurnal Tide

Migrating diurnal tide in the MLT region is examined by the application of Hough mode decomposition with the tide delineated from the SABER/TIMED temperatures over 2002-2006. The decomposition results show that in the height range 60-100km, the （1, 1） mode is the most predominant among eight leading Hough modes including four propagating and four trapped modes. It exhibits a sustained maximum at 97 km and significant semi-annual oscillation. Additionally, a novel feature of inter-annual variation with period of about two years is clearly seen in the （1, 1） mode, e.g., repeated maxima are seen at the March equinox of 2002, 2004 and 2006, respectively. This feature is further manifested by the tidal amplitudes in the height range 70-100km in the height-time cross-section at the equator. It is likely of the QBO as the height range just coincides to where the zonal mean zonal winds derived by using the UARS data exhibiting the QBO. The other results show that the （1, 2） mode is important at 〈 80 km exhibiting comparable amplitude to that of the （1, 1） mode, and in particular the nearly anti-correlation with the （1, 1） mode. The tide at about 85 km is suggested of rather complex as the four trapped modes exhibit maximum at these heights, which indicates the presence of local excitations or sources at below.     

Annual Variation and Global Structures of The DE3 Tide

The SABER/TIMED temperatures taken in 2002 2006 are used to delineate the tidal signals in the middle and upper atmosphere. Then the Hough mode decomposition is applied with the DE3 tide, and the overall features of the seasonal variations and the complete global structures of the tide are observed. Investigation results show that the tide is most prominent at 110km with the maximal amplitude of 〉 9K, and exhibits significant seasonal variation with its maximum amplitude always occurring in July every year. Results from the Hough mode decomposition reveal that the tide is composed primarily of two leading propagating Hough modes, i.e., the （-3, 3） and the （-3, 4） modes, thus is equatorially trapped. Estimation of the mean amplitude of the Hough modes show that the （-3, 3） mode and （-3, 4） mode exhibit maxima at 110km and 90km, respectively. The （-3, 3） mode plays a predominant role in shaping the global latitude-height structure of the tide, e.g., the vertical scale of 〉 50 km at the equator, and the annual course. Significant influence of the （-3, 4） mode is found below 90 km, where the tide exhibits anti-symmetric structure about the equator; meanwhile the tide at northern tropical latitudes exhibits smaller vertical wavelength of about 30 km.     

A Scanning Multi-Axis Differential Optical Absorption Spectroscopy System for Measurement of Tropospheric NO2 in Beijing

A scanning multi-axis differential optical absorption spectroscopy （DOAS） system is developed for monitoring tropospheric NO2 abundance. Measurements at different viewing angles near the horizon can be performed sequentially with one telescope collecting scattered sunlight reflected by a moving mirror. Tropospheric NO2 diurnal variations can be derived from slant column densities （SCDs） of different elevation angles. The result from a field campaign in Beijing in summer of 2005 reveals potential possibility for the monitoring of tropospheric NO2 by multi-axis DOAS technique.     

On the Doppler distortion of the sea-wave spectra

Discussions on a form of a frequency spectrum of wind-driven sea waves just above the spectral maximum have continued for the last three decades. In 1958 Phillips made a conjecture that wave breaking is the main mechanism responsible for the spectrum formation [O.M. Phillips, J. Fluid Mech. 4 (1958) 426]. That leads to the spectrum decay ∼ω⁻⁵, where ω is the frequency of waves. There is a contradiction between the numerous experimental data and this spectrum. Experiments frequently show decay ∼ω⁻⁴ [Y. Toba, J. Oceanogr. Soc. Japan 29 (1973) 209; M.A. Donelan, J. Hamilton, W.H. Hui, Phil. Trans. R. Soc. London A315 (1985) 509; P.A. Hwang, et al., J. Phys. Oceanogr. 30 (1999) 2753]. There are several ways of the explanation of this phenomenon. One of them (proposed by Banner [M.L. Banner, J. Phys. Oceanogr. 20 (1990) 966]) takes into account the Doppler effect due to surface circular currents generated by underlying waves in the Phillips model.In this article the influence of the Doppler effect on an arbitrary averaged spectrum is considered using both analytic and numerical approaches. Although we mostly concentrated on the very important case of Phillips model, the developed technique and general formula can be used for the analysis of other spectra.For the particular case of Phillips spectra we got analytic asymptotics in the vicinity of spectral maximum and for high frequencies. Results were obtained for two most important angular dependences of the spectra: isotropic and strongly anisotropic. Together with the analytic investigation we performed numerical calculations in a wide range of frequencies. Both high and low frequency asymptotics are in very good agreement with the numerical results.It was shown that at least at low frequencies, the correction to the spectrum due to the Doppler shift is negligible. At high frequencies there is an asymptotic with tail ∼ω⁻³.     

Measurements of toluene and other aromatic hydrocarbons by differential-absorption LIDAR in the near-ultraviolet

The first measurements of toluene by differential-absorption LIDAR in the near-ultraviolet spectral region are reported. A pulse energy of 4.5 mJ was used for the measurement, generated by frequency-doubling the output from a tunable dye laser in beta-barium borate. The magnitude of spectral interference from other pollutant species has been calculated and the extension of the system to measure other aromatic hydrocarbons in the same spectral region is discussed.     

Resonant nonlinear interactions between atmospheric waves in the polar summer mesopause region

Data obtained from the mobile SOUSY VHF radar at And(ya/Norway in summer 1987 have been used to study the nonlinear interactions between planetary waves, tides and gravity waves in the polar mesosphere, and the instability of background atmosphere above the mesopause. It is observed that 35-h planetary wave, diurnal, semidiurnal and terdiurnal tides are the prominent perturbations in the Lomb-Scargle spectra of the zonal wind component. By inspecting the frequency combinations, several triads are identified. By bispectral analysis it is shown that most bispectral peaks stand for quadratic coupling between tidal harmonics or between tide and planetary or gravity wave, and the height dependence of bispectral peaks reflects the variation of wave-wave interactions. Above the mesopause, the occurrence heights of the maximum L-S power spectral peaks corresponding to the prominent wave components tend to increase with their frequencies. This may result from the process in which two low frequency waves interact to generate a high frequency wave. Intensities of the planetary wave and tides increase gradually, arrive at their maxima, and then decay quickly in turn with increasing height. This kind of scene correlates with a "chain" of wave-wave resonant interactions that shifts with height from lower frequency segment to higher frequency segment. By instability analysis, it is observed that above the mesopause, the Richardson number becomes smaller and smaller with height, implying that the turbulent motion grows stronger and stronger and accordingly the background atmosphere more and more instable. It is suggested that the wave-wave sum resonant interaction and the wave dissipation due to instability are two dominant dynamical processes that occur in the mesopause region. The former invokes the energy transfer from lower frequency waves to higher frequency waves. The latter results in the heating of the atmosphere and accelerating of the background flow.     

Improving the description of sunglint for accurate prediction of remotely sensed radiances

The bidirectional reflection distribution function (BRDF) of the ocean is a critical boundary condition for radiative transfer calculations in the coupled atmosphere-ocean system. Existing models express the extent of the glint-contaminated region and its contribution to the radiance essentially as a function of the wind speed. An accurate treatment of the glint contribution and its propagation in the atmosphere would improve current correction schemes and hence rescue a significant portion of data presently discarded as “glint contaminated”. In current satellite imagery, a correction to the sensor-measured radiances is limited to the region at the edge of the glint, where the contribution is below a certain threshold. This correction assumes the sunglint radiance to be directly transmitted through the atmosphere. To quantify the error introduced by this approximation we employ a radiative transfer code that allows for a user-specified BRDF at the atmosphere-ocean interface and rigorously accounts for multiple scattering. We show that the errors incurred by ignoring multiple scattering are very significant and typically lie in the range 10-90%. Multiple reflections and shadowing at the surface can also be accounted for, and we illustrate the importance of such processes at grazing geometries.     

Comment on breakup densities of hot nuclei

In [V.E. Viola et al., Phys. Rev. Lett. 93 (2004) 132701, D.S. Bracken et al., Phys. Rev. C 69 (2004) 034612] the observed decrease in spectral peak energies of IMFs emitted from hot nuclei was interpreted in terms of a breakup density that decreased with increasing excitation energy. Subsequently, Raduta et al. [Ad. Raduta et al., Phys. Lett. B 623 (2005) 43] performed MMM simulations that showed decreasing spectral peaks could be obtained at constant density. In this Letter we point out that this apparent inconsistency is due to a selective comparison of theory and data that overlooks the evolution of the fragment multiplicities as a function of excitation energy.     

Generation of flexural waves in plates by laser-initiated airborne shock waves

Results of the semi-analytical modelling of the interaction of laser-initiated airborne shock waves with an infinite horizontally positioned elastic plate are presented. The impact of the airborne shock waves on the plate is approximated by a cylindrically diverging surface force resulting from the pressure of the incident and reflected shock waves. This force is then represented in the wavenumber-frequency domain by means of Hankel and Fourier transforms that are carried out numerically so that the interaction problem can be solved using the Green’s function method. The resulting frequency spectra and time histories of generated flexural wave pulses are calculated for different values of laser pulse energy and for different heights of the laser beam focusing above the plate surface. The theoretical results obtained are compared with the results of laboratory measurements of the interaction of laser-generated acoustic shocks with a large plastic plate. The comparison shows reasonably good agreement between the semi-analytical predictions and data.     

Measured wavenumber: frequency spectrum associated with acoustic and aerodynamic wall pressure fluctuations

Direct measurements of the wavenumber-frequency spectrum of wall pressure fluctuations beneath a turbulent plane channel flow have been performed in an anechoic wind tunnel. A rotative array has been designed that allows the measurement of a complete map, 63×63 measuring points, of cross-power spectral densities over a large area. An original post-processing has been developed to separate the acoustic and the aerodynamic exciting loadings by transforming space-frequency data into wavenumber-frequency spectra. The acoustic part has also been estimated from a simple Corcos-like model including the contribution of a diffuse sound field. The measured acoustic contribution to the surface pressure fluctuations is 5% of the measured aerodynamic surface pressure fluctuations for a velocity and boundary layer thickness relevant for automotive interior noise applications. This shows that for aerodynamically induced car interior noise, both contributions to the surface pressure fluctuations on car windows have to be taken into account.     

Recent developments in the line-by-line modeling of outgoing longwave radiation

High frequency resolution radiative transfer model calculations with the Atmospheric Radiative Transfer Simulator (ARTS) were used to simulate the clear-sky outgoing longwave radiative flux (OLR) at the top of the atmosphere. Compared to earlier calculations by Clough and coworkers the model used a spherical atmosphere instead of a plane parallel atmosphere, updated spectroscopic parameters from HITRAN, and updated continuum parameterizations from Mlawer and coworkers. These modifications lead to a reduction in simulated OLR by approximately 4.1%, the largest part, approximately 2.5%, being due to the absence of the plane parallel approximation. As a simple application of the new model, the sensitivity of OLR to changes in humidity, carbon dioxide concentration, and temperature were investigated for different cloud-free atmospheric scenarios. It was found that for the tropical scenario a 20% change in humidity has a larger impact than a doubling of the carbon dioxide concentration. The sensitive altitude region for temperature and humidity changes is the entire free troposphere, including the upper troposphere where humidity data quality is poor.     

SODAR study of the boundary layer over moscow for air-pollution application

The 24-hour SODAR measurements of the atmospheric boundary-layer parameters over Moscow were carried out during one month in the summer of 1990 and one month in the winter of 1991 at three points within the city and suburbs. The simultaneous measurements of the concentrations of several pollutants were also carried out at one of these points. The relations between local concentrations of some pollutants and the parameters measured by SODAR (mixing height and wind speed) are revealed. This fact confirms the usefulness of SODAR observations for air-pollution meteorology. The statistics of the boundary-layer parameters in summer and winter seasons as well as the data on their spatial variations over the city were obtained.     

A computationally efficient scheme for the non-linear diffusion equation

This Letter proposes a new numerical scheme for integrating the non-linear diffusion equation. It is shown that it is linearly stable. Some tests are presented comparing this scheme to a popular decentered version of the linearized Crank-Nicholson scheme, showing that, although this scheme is slightly less accurate in treating the highly resolved waves, (i) the new scheme better treats highly non-linear systems, (ii) better handles the short waves, (iii) for a given test bed turns out to be three to four times more computationally cheap, and (iv) is easier in implementation.     

A nonlinear approach to analyse the development of tropical disturbances

The development of atmospheric disturbances in the tropical region is explained using vibrational resonance, a nonlinear phenomenon. As the Lorenz system is the most plausible model to describe the convective process in a tropical region, the influence of vertical wind shear and tropical waves on the system leading to tropical cyclone has been investigated. The response of the convective region towards vertical wind shear and tropical waves is numerically studied. It was found that the response of the convective system decreases with the absence of any of these environmental factors. The dynamics of the system including resonance phenomenon is studied using phase portraits and Lyapunov dimension. Further, Lyapunov dimension is employed here to characterize the occurrence of resonant peaks.     

Polarization Effects Due to Scattering of Microwave Radiation in ihe Summer Cloudy Atmosphere

We present the results of the spectral analysis of polarization of the thermal microwave emission from the summer cloudy atmosphere at 37 and 94 GHz. A significant polarization of the microwave emission from summer clouds is revealed, which is attributed to scattering of the thermal emission from the atmosphere by melted ice crystals in the melting layer. Based on a model of polarized radiation transfer in the mixed clouds containing melted ice crystals and supercooled water drops, we interpret the experimental data with allowance for all orders of scattering. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 4, pp. 314–326, April 2005.     

Surface reverberation spectrum of underwater sound

A general formulation is derived for the power spectrum of fluctuations in the signal received by way of reflection from a rough sea surface, in terms of an arbitrary wavenumber-frequency spectrum of the surface waves and an arbitrary source directivity function. The formulation is then applied to the specific case of backscatter for which the extreme cases of acoustically slightly rough and very rough sea surfaces are examined in detail. The results of the analysis are compared with experiments, and with the somewhat more restricted results of other theoretical work.     

Effect of changes of the HITRAN database on transmittance calculations in the near-infrared region

In order to retrieve from high spectral resolution measurements with high accuracy, it is necessary to be able to evaluate the transmittance precisely. However, the uncertainty of the spectroscopic parameters is one of the most important contributions that affect the accuracy of transmittance. HITRAN is a compilation of spectroscopic parameters which has been updated several times. The transmittance calculations using the line parameters from the HITRAN’2000 database and the HITRAN’2004 database have been compared over the near infrared range from 4200 to 10,000 cm^?1. The differences between calculated transmittances over this spectral range are mainly caused by changes of the line parameters for H₂O, CO₂ and CH₄. For the tropical atmosphere, the differences are very prominent. Transmittance calculations for the sub-arctic winter atmosphere are less sensitive to the changes in the HITRAN database than those for the tropical atmosphere; but, the changes of line parameters still can not be ignored when considering the relative differences. For example, the relative difference is ～35% at 5073.3 cm^?1 with 0.2 cm^?1 spectral resolution. The comparisons have shown that it is important to pay attention to the changes of line parameters of the HITRAN database or to use the latest edition so as to improve the accuracy of atmospheric sounding with high spectral resolution.     

On the use of SODAR data to estimate mixing height

Estimation of the mixing height is one of the most common applications of SODAR data for more than twenty years and SODAR has been shown to provide reliable results under a great variety of meteorological and site conditions. Nevertheless there are still some unsolved questions. The paper gives a brief review of results obtained during the last two decades. Additionally some of the open problems are discussed in more detail. These are the determination of the stable boundary layer height from digitized SODAR data, its relation to other common height scales, its parameterization, and finally the estimation of the height of a deep convective boundary layer, exceeding the SODAR probing range.