Dynamic Model Atmospheres Research Articles

The dynamic atmospheres of Mira stars: comparing the CODEX models to PTI time series of TU Andromedae

Our comprehension of stellar evolution on the AGB still faces many difficulties. To improve on this, a quantified understanding of large-amplitude pulsator atmospheres and interpretation in terms of their fundamental stellar parameters are essential. We wish to evaluate the effectiveness of the recently released CODEX dynamical model atmospheres in representing M-type Mira variables through a confrontation with the time-resolved spectro-photometric and interferometric PTI data set of TU And. We calibrated the interferometric K-band time series to high precision. This results in 50 nights of observations, covering 8 subsequent pulsation cycles. At each phase, the flux at 2.2$\mu$m is obtained, along with the spectral shape and visibility points in 5 channels across the K-band. We compared the data set to the relevant dynamical, self-excited CODEX models. Both spectrum and visibilities are consistently reproduced at visual minimum phases. Near maximum, our observations show that the current models predict a photosphere that is too compact and hot, and we find that the extended atmosphere lacks H2O opacity. Since coverage in model parameter space is currently poor, more models are needed to make firm conclusions on the cause of the discrepancies. We argue that for TU And, the discrepancy could be lifted by adopting a lower value of the mixing length parameter combined with an increase in the stellar mass and/or a decrease in metallicity, but this requires the release of an extended model grid.

Aggressive shadowing of a low-dimensional model of atmospheric dynamics

Predictions of the future state of the Earth’s atmosphere suffer from the consequences of chaos: numerical weather forecast models quickly diverge from observations as uncertainty in the initial state is amplified by nonlinearity. One measure of the utility of a forecast is its shadowing time, informally given by the period of time for which the forecast is a reasonable description of reality. The present work uses the Lorenz ’96 coupled system, a simplified nonlinear model of atmospheric dynamics, to extend a recently developed technique for lengthening the shadowing time of a dynamical system. Ensemble forecasting is used to make forecasts with and without inflation, a method whereby the ensemble is regularly expanded artificially along dimensions whose uncertainty is contracting. The first goal of this work is to compare model forecasts, with and without inflation, to a true trajectory created by integrating a modified version of the same model. The second goal is to establish whether inflation can increase the maximum shadowing time for a single optimal member of the ensemble. In the second experiment the true trajectory is known a priori, and only the closest ensemble members are retained at each time step, a technique known as stalking. Finally, a targeted inflation is introduced to both techniques to reduce the number of instances in which inflation occurs in directions likely to be incommensurate with the true trajectory. Results varied for inflation, with success dependent upon the experimental design parameters (e.g. size of state space, inflation amount). However, a more targeted inflation successfully reduced the number of forecast degradations without significantly reducing the number of forecast improvements. Utilized appropriately, inflation has the potential to improve predictions of the future state of atmospheric phenomena, as well as other physical systems.

백두산 화산 분출물 확산 예측에 대기흐름장 평균화가 미치는 영향

백두산 화산분출물의 이류와 확산 예측 특성을 살펴보기 위하여 3차원 대기역학 모형인 WRF와 입자 확산 모형인 FLEXPART를 결합하여 다양한 수치실험을 실시하였다. 기상자료의 시간 평균화에 따른 영향을 보기 위하여 네가지 서로 다른 평균화 기간을 가진 수치 실험을 실시하였다. 본 연구에 적용된 기상자료의 평균화 기간은 각각 1개월, 10일, 3일이다. 또한 평균화를 실시하지 않은 실시간자료를 이용한 수치실험도 실시하였다. 기상자료의 평균화 시간이 길어질수록 주풍성분인 동서 방향의 운동이 뚜렷해지고, 짧을수록 주풍의 법선 방향인 남북 운동이 명확하게 나타나며, 화산분출물을 가정한 입자의 확산 역시 동일한 특성이 나타난다. 상하층의 바람은 강도의 차이가 명확하고, 평준화 기간에 따른 영향이 다르게 나타나기 때문에 상층입자와 하층입자의 이동과 지상 침적이 다양하게 나타난다. 또한 한반도의 지상 침적은 방출고도 2 km 이하의 입자가 주로 영향을 미친다. 따라서 기상자료의 평균화 시간 간격이 화산분출물의 지상 침적을 결정하는 하나의 요인으로 작용하기 때문에, 확산 실험 전에 적절한 기상자료의 시간평균을 결정할 필요가 있다. In order to clarify the advection and dispersion characteristics of volcanic tephra to be emitted from the Mt. Baekdu, several numerical experiments were carried out using three-dimensional atmospheric dynamic model, Weather and Research Forecast (WRF) and Laglangian particles dispersion model FLEXPART. Four different temporally averaged meteorological values including wind speed and direction were used, and their averaged intervals of meteorological values are 1 month, 10 days, and 3days, respectively. Real time simulation without temporal averaging is also established in this study. As averaging time of meteorological elements is longer, wind along the principle direction is stronger. On the other hands, the tangential direction wind tends to be clearer when the time become shorten. Similar tendency was shown in the distribution of volcanic tephra because the dispersion of particles floating in the atmosphere is strongly associated with wind pattern. Wind transporting the volcanic tephra is divided clearly into upper and lower region and almost ash arriving the Korean Peninsula is released under 2 km high above the ground. Since setting up the temporal averaging of meteorological values is one of the critical factors to determine the density of tephra in the air and their surface deposition, reasonable time for averaging meteorological values should be established before the numerical dispersion assessment of volcanic tephra.

Inhomogeneities in molecular layers of Mira atmospheres

We obtained K-band spectro-interferometric observations of the Miras R Cnc, X Hya, W Vel, and RW Vel with a spectral resolution of 1500 using the VLTI/AMBER instrument. We obtained concurrent JHKL photometry using the the Mk II instrument at the SAAO. Our sources have wavelength-dependent visibility values that are consistent with earlier low-resolution AMBER observations of S Ori and with the predictions of dynamic model atmosphere series based on self-excited pulsation models. The wavelength-dependent UD diameters show a minimum near the near-continuum bandpass at 2.25 um. They increase by up to 30% toward the H2O band at 2.0 um and by up to 70% at the CO bandheads. The dynamic model atmosphere series show a consistent wavelength-dependence, and their parameters such as the visual phase, effective temperature, and distances are consistent with independent estimates. The closure phases have significantly wavelength-dependent non-zero values indicating deviations from point symmetry. For example, the R Cnc closure phase is 110 degr in the 2.0 um H2O band, corresponding for instance to an additional unresolved spot contributing 3% of the total flux at a separation of ~4 mas. Our observations are consistent with the predictions of the latest dynamic model atmosphere series based on self-excited pulsation models. The wavelength-dependent radius variations are interpreted as the effect of molecular layers. The wavelength-dependent closure phase values are indicative of deviations from point symmetry at all wavelengths, thus a complex non-spherical stratification of the extended atmosphere. In particular, the significant deviation from point symmetry in the H2O band is interpreted as a signature on large scales of inhomogeneities or clumps in the water vapor layer. The observed inhomogeneities might be caused by pulsation- and shock-induced chaotic motion in the extended atmosphere.

Connection of periodic orbits and variability patterns of circulation for the barotropic model of atmospheric dynamics

We have investigated the relationship between periodic trajectories of barotropic atmospheric model and the modes of the model variability. In particular, we have studied the nature of “25 day” mode of variability (Branstator, 1987; Kushnir 1987). This mode arises as a first complex empirical orthogonal function (or “Hilbert EOF” according to (H. von Storch, Zwiers)) for a given system and is a dominant rotational component of the system dynamics. It was shown that the mode structure coincides with several least unstable periodic orbits of the system. The phase portrait of the system in the plane of the first complex EOF has regular shape with maximum of the probability density function in the vicinity of these weakly unstable periodic orbits.

Precision Orbit Derived Total Density

Precision Orbit Derived Total Density

Multiyear Statistics of 2D Shortwave Radiative Effects at Three ARM Sites

Abstract This study examines the importance of horizontal photon transport effects, which are not considered in the 1D calculations of solar radiative heating used by most atmospheric dynamical models. In particular, the paper analyzes the difference between 2D and 1D radiative calculations for 2D vertical cross sections of clouds that were observed at three sites over 2–3-yr periods. The results show that 2D effects increase multiyear 24-h average total solar absorption by about 4.1, 1.2, and 0.3 W m−2 at tropical, midlatitude, and arctic sites, respectively. However, 2D effects are often much larger than these average values, especially for high sun and for convective clouds. The results also reveal a somewhat unexpected behavior, namely, that horizontal photon transport often enhances solar heating even for oblique sun. These findings underscore the need for fast radiation calculation methods that can allow atmospheric dynamical simulations to consider the inherently multidimensional nature of shortwave radiative processes.

PHOTOMETRIC AND SPECTRAL SIGNATURES OF THREE-DIMENSIONAL MODELS OF TRANSITING GIANT EXOPLANETS

Using a three-dimensional general circulation model, we create dynamical model atmospheres of a representative transiting giant exoplanet, HD 209458b. We post-process these atmospheres with an opacity code to obtain transit radius spectra during the primary transit. Using a spectral atmosphere code, we integrate over the face of the planet seen by an observer at various orbital phases and calculate light curves as a function of wavelength and for different photometric bands. The products of this study are generic predictions for the phase variations of a zero-eccentricity giant planet's transit spectrum and of its light curves. We find that for these models the temporal variations in all quantities and the ingress/egress contrasts in the transit radii are small (<1.0%). Moreover, we determine that the day/night contrasts and phase shifts of the brightness peaks relative to the ephemeris are functions of photometric band. The J, H, and K bands are shifted most, while the IRAC bands are shifted least. Therefore, we verify that the magnitude of the downwind shift in the planetary "hot spot" due to equatorial winds is strongly wavelength dependent. The phase and wavelength dependence of light curves, as well as the associated day/night contrasts, can be used to constrain the circulation regime of irradiated giant planets and to probe different pressure levels of a hot Jupiter atmosphere. We posit that though our calculations focus on models of HD 209458b, similar calculations for other transiting hot Jupiters in low-eccentricity orbits should yield transit spectra and light curves of a similar character.

Abundance analysis for long period variables

(abbreviated) Measuring the surface abundances of AGB stars is an important tool for studying the effects of nucleosynthesis and mixing in the interior of low- to intermediate mass stars during their final evolutionary phases. The atmospheres of AGB stars can be strongly affected by stellar pulsation and the development of a stellar wind, though, and the abundance determination of these objects should therefore be based on dynamic model atmospheres. We investigate the effects of stellar pulsation and mass loss on the appearance of selected spectral features (line profiles, line intensities) and on the derived elemental abundances by performing a systematic comparison of hydrostatic and dynamic model atmospheres. High-resolution synthetic spectra in the near infrared range were calculated based on two dynamic model atmospheres (at various phases during the pulsation cycle) as well as a grid of hydrostatic COMARCS models. Equivalent widths of a selection of atomic and molecular lines were derived in both cases and compared with each other. In the case of the dynamic models, the equivalent widths of all investigated features vary over the pulsation cycle. A consistent reproduction of the derived variations with a set of hydrostatic models is not possible, but several individual phases and spectral features can be reproduced well with the help of specific hydrostatic atmospheric models. In addition, we show that the variations in equivalent width that we found on the basis of the adopted dynamic model atmospheres agree qualitatively with observational results for the Mira R Cas over its light cycle. The findings of our modelling form a starting point to deal with the problem of abundance determination in strongly dynamic AGB stars (i.e., long-period variables).

Line formation in AGB atmospheres including velocity effects

<i>Context. <i/>Towards the end of the evolutionary stage of the asymptotic giant branch (AGB) the atmospheres of evolved red giants are considerably influenced by radial pulsations of the stellar interiors and developing stellar winds. The resulting complex velocity fields severely affect molecular line profiles (shapes, time-dependent shifts in wavelength, multiple components) observable in near-infrared spectra of long period variables. Time-series high-resolution spectroscopy allows us to probe the atmospheric kinematics and thereby study the mass loss process.<i>Aims. <i/>With the help of model calculations the complex line formation process in AGB atmospheres was explored with the focus on velocity effects. Furthermore, we aimed for atmospheric models which are able to quantitatively reproduce line profile variations found in observed spectra of pulsating late-type giants.<i>Methods. <i/>Models describing pulsation-enhanced dust-driven winds were used to compute synthetic spectra under the assumptions of chemical equilibrium and LTE. For this purpose, we used molecular data from line lists for the considered species and solved the radiative transfer in spherical geometry including the effects of velocity fields. Radial velocities (RV) derived from Doppler-shifted (components of) synthetic line profiles provide information on the gas velocities in the line-forming region of the spectral features. In addition, we made use of radial optical depth distributions to give estimates for the layers where lines are formed and to illustrate the effects of velocities in the line formation process.<i>Results. <i/>Assuming uniform gas velocities for all depth points of an atmospheric model we estimated the conversion factor between gas velocities and measured RVs to <i>p<i/> = <i>u<i/><sub>gas<sub/>/RV <i>≈<i/> 1.2–1.5. On the basis of dynamic model atmospheres and by applying our spectral synthesis codes we investigated in detail the finding that various molecular features in AGB spectra originate at different geometrical depths of the very extended atmospheres of these stars. We show that the models are able to quantitatively reproduce the characteristic line profile variations of lines sampling the deep photosphere (CO <i>Δ<i/><i>v<i/> = 3, CN) of Mira variables and the corresponding discontinuous, S-shaped RV curve. The global velocity fields (traced by different features) of typical long-period variables are also realistically reproduced. Possible reasons for discrepancies concerning other modelling results (e.g. CO <i>Δ<i/><i>v<i/> = 2 lines) are outlined. In addition, we present a model showing variations of CO <i>Δ<i/><i>v<i/> = 3 line profiles comparable to observed spectra of semiregular variables and discuss that the non-occurence of line doubling in these objects may be due to a density effect.<i>Conclusions. <i/>The results of our line profile modelling are another indication that the dynamic models studied here are approaching a realistic representation of the outer layers of AGB stars with or without mass loss.

보수성 도로 포장재의 증발효율 변화에 의한 중규모 순환장 특성 분석

보수성 포장재가 지표면 열수지와 중규모 순환장에 미치는 영향을 파악하기 위하여 수치실험과 야외 관측을 실시하였다. 수치실험에 이용된 모형은 LCM(Local Circulation Model)이며, 야외 관측은 대기가 안정되어 날씨가 맑은 2007년 7월 19일 실시되었다. 야외 관측실험에서 보수성 포장재 지표면 온도의 최대치는 1430 LST에서 <TEX>$41.2^{\circ}C$</TEX>이고, 보수성 재료가 도포되어 있지 않은 일반 아스팔트보다 <TEX>$16.1^{\circ}C$</TEX> 낮게 관측되었다. 수치실험에서는 증발효율 0.3을 가정한 case BET03에서 관측과 가장 유사한 값을 나타내었다. 이때 현열과 잠열플럭스는 각각 227 와 229 <TEX>$W/m^2$</TEX>이다. 수치실험 결과, 보수성 포장재는 낮은 지표면 온도, 혼합고와 관련된 잠열플럭스를 높이는 경향이 나타난다. 보수성 포장재에 의한 잠열플럭스의 불연속은 교외풍과 같은 중규모 순환장의 발달을 강화시키는 역할을 한다. Field observation and numerical experiments were conducted to understand the impact of water retention pavement on the surface heat budget and on the regional circulation. The numerical model applied in this study is the atmospheric dynamic model Local Circulation Model (LCM) with two dimensional grid system, and a field observation was carried out under the clear sky and calm conditions of the weather on 19 July 2007. In the field observation, the maximum value of surface temperature on pavement covered with water retention material reached the <TEX>$41.2^{\circ}C$</TEX> at 1430 LST and the values was lower for <TEX>$16.1^{\circ}C$</TEX> than that of asphalt without the material. The Case BET03 assumed to be 0.3 for the surface evaporation efficiency was in good agreement with the observation and its sensible and latent heat fluxes were numerically estimated to be 229 and 227 <TEX>$W/m^2$</TEX>, respectively. Results of the numerical experiments demonstrated that the water retention pavement tends to induce the increase of latent heat flux associated with the lower surface temperature and mixing height during the daytime. Discontinuity of latent heat caused by the water retention pavement also tends to promote the development of mesoscale circulation called as land-land breeze or country breeze.

Interferometric properties of pulsating C-rich AGB stars

We present the first theoretical study on center-to-limb variation (CLV) properties and relative radius interpretation for narrow and broad-band filters, on the basis of a set of dynamic model atmospheres of C-rich AGB stars. We computed visibility profiles and the equivalent uniform disc radii (UD-radii) in order to investigate the dependence of these quantities upon the wavelength and pulsation phase. After an accurate morphological analysis of the visibility and intensity profiles determined in narrow and broad-band filter, we fitted our visibility profiles with a UD function simulating the observational approach. UD-radii have been computed using three different fitting-methods to investigate the influence of the sampling of the visibility profile: single point, two points and least square method. The intensity and visibility profiles of models characterized by mass loss show a behaviour very different from a UD. We found that UD-radii are wavelength dependent and this dependence is stronger if mass loss is present. Strong opacity contributions from C2H2 affect all radius measurements at 3 micron and in the N-band, resulting in higher values for the UD-radii. The predicted behaviour of UD-radii versus phase is complicated in the case of models with mass loss, while the radial changes are almost sinusoidal for the models without mass loss. Compared to the M-type stars, for the C-stars no windows for measuring the pure continuum are available.

Dynamics of Prediction Errors under the Combined Effect of Initial Condition and Model Errors

Abstract The transient evolution of prediction errors in the short to intermediate time regime is considered under the combined effect of initial condition and model errors. Some generic features are brought out and connected with intrinsic properties. Under the assumption of small uncorrelated initial errors and of small parameter errors, the conditions of existence of a time at which the mean quadratic error reaches a minimum and of a crossover time at which the contribution of initial condition errors matches that of model errors are determined. The results are illustrated and tested on representative low-order models of atmospheric dynamics exhibiting bistability, saddle-point behavior, and chaotic behavior.

A simulation study of short-range atmospheric dispersion for hypothetical air-borne effluent releases using different turbulent diffusion methods

Radiological impact due to hypothetical air-borne effluent releases for an upcoming fast reactor (PFBR), at a tropical coastal site in Kalpakkam is studied using the HYSPLIT dispersion model. Short range air dispersion simulations are conducted with HYSPLIT for a weakly forced synoptic condition on 3rd March, 2008 with three turbulent diffusion methods, i.e., standard velocity deformation (A), short range isotropic similarity (B) and turbulent kinetic energy (TKE) (C) schemes to assess their performance in predicting the dose distribution at a local scale. The time varying 3-d meteorological parameters for the case study are predicted using a nested grid meso-scale dynamical atmospheric model MM5. Results indicate that the velocity deformation method gives spatially more complex dose pattern while the short-range similarity and TKE methods provide smoother horizontal dose profiles. The downwind dose in different pathways due to elevated releases is found to be the highest for the method A followed by B and C. For the ground releases, the TKE method produced higher doses than the other two. The difference in the dose values from the three methods is due to the variation in the horizontal and vertical mixing calculation and the assumptions involved in the respective methods. The total dose at the site boundary from different pathways is highest from the TKE method. Values from all the methods are about one to two orders less than the values given by a Gaussian Plume model for similar atmospheric conditions. The total dose estimated from the TKE method is 20.62 mSv at the release location and 1.25 mSv at the site boundary.

Achievable Moments NDI-based Fault Tolerant Thrust Vector Control of an Atmospheric Vehicle during Ascent

In this article the design of a fault tolerant thrust vector control (TVC) for the automated ascent of the Hopper reusable launch vehicle is presented. The considered ascent starts at the pull-up maneuver performed immediately after horizontal take off and ends at main-engine-cut-off. The TVC law uses nonlinear dynamic inversion (NDI) to obtain the required engine gimbal deflections for robust tracking of the angle of attack and bank angle from a guidance law. The NDI–based TVC is characterized by the use of the Hopper's engine redundancy layout and by the interpretation of NDI as an achievable dynamics identification scheme. The resulting TVC design has been validated using a Monte Carlo campaign with realistic aerodynamic mismatch, corrupted measurements, parametric uncertainty and high fidelity atmospheric and 6DoF vehicle dynamics models. Evaluation of the design with a wide array of thrust and engine gimbal faults yields that the resulting TVC improves the closed loop fault tolerant capabilities.

SiO maser emission in Miras

We describe a combined dynamic atmosphere and maser propagation model of SiO maser emission in Mira variables. This model rectifies many of the defects of an earlier model of this type, particularly in relation to the infra-red (IR) radiation field generated by dust and various wavelength-dependent, optically thick layers. Modelled masers form in rings with radii consistent with those found in VLBI observations and with earlier models. This agreement requires the adoption of a radio photosphere of radius approximately twice that of the stellar photosphere, in agreement with observations. A radio photosphere of this size renders invisible certain maser sites with high amplification at low radii, and conceals high-velocity shocks, which are absent in radio continuum observations. The SiO masers are brightest at an optical phase of 0.1 to 0.25, which is consistent with observed phase-lags. Dust can have both mild and profound effects on the maser emission. Maser rings, a shock and the optically thick layer in the SiO pumping band at 8.13µmappear to be closely associated in three out of four phase samples.

Winds of M-type AGB stars driven by micron-sized grains

Context. In view of the recent problem regarding the dynamical modelling of winds of M-type AGB stars (insufficient radiation pressure on silicate grains), some of the basic assumptions of these models need to be re-evaluated critically. Aims. Accepting the conclusion that non-grey effects will force silicate grains to be virtually Fe-free, the viability of driving winds with micron-sized Fe-free silicates, instead of small particles, is examined. Methods. Using both simple estimates and detailed dynamical atmosphere and wind models, it is demonstrated that radiation pressure on Fe-free silicate grains is sufficient to drive outflows if the restriction to the small particle limit is relaxed, and prevailing thermodynamic conditions allow grains to grow to sizes in the micrometer range. Results. The predicted wind properties, such as mass loss rates and outflow velocities, are in good agreement with observations of M-type AGB stars. Due to a self-regulating feedback between dust condensation and wind acceleration, grain growth naturally comes to a halt at particle diameters of about 1 μm. Conclusions. The most efficient grain sizes to drive winds are in a rather narrow interval around 1 μm. These values are set by the wavelength range corresponding to the flux maximum in typical AGB stars, and are very similar to interstellar grains.

HN Peg B: A Test of Models of the L to T Dwarf Transition

Luhman and collaborators recently discovered an early-T dwarf companion to the G0 dwarf star HN Peg, using Spitzer Infrared Array Camera (IRAC) images. Companionship was established on the basis of the common proper motion inferred from 1998 Two Micron All Sky Survey images and the 2004 IRAC images. In this paper we present new near-infrared imaging data which confirms the common proper motion of the system. We also present new 3 - 4 um spectroscopy of HN Peg B, which provides tighter constraints on both the bolometric luminosity determination and the comparison to synthetic spectra. New adaptive optics imaging data are also presented, which shows the T dwarf to be unresolved, providing limits on the multiplicity of the object. We use the age, distance and luminosity of the solar-metallicity T dwarf to determine its effective temperature and gravity, and compare synthetic spectra with these values, and a range of grain properties and vertical mixing, to the observed 0.8 - 4.0 um spectra and mid-infrared photometry. We find that models with temperature and gravity appropriate for the older end of the age range of the system (0.5 Gyr) can do a reasonable job of fitting the data, but only if the photospheric condensate cloud deck is thin, and if there is significant vertical mixing in the atmosphere. Dwarfs such as HN Peg B, with well-determined metallicity, radius, gravity and temperature will allow development of dynamical atmosphere models, leading to the solution of the puzzle of the L to T dwarf transition.

Data assimilation in weather forecasting: a case study in PDE-constrained optimization

Variational data assimilation is used at major weather prediction centers to produce the initial conditions for 7- to 10-day weather forecasts. This technique requires the solution of a very large data-fitting problem in which the major element is a set of partial differential equations that models the evolution of the atmosphere over a time window for which observational data has been gathered. Real-time solution of this difficult computational problem requires sophisticated models of atmospheric physics and dynamics, effective use of supercomputers, and specialized algorithms for optimization and linear algebra. The optimization algorithm can be accelerated by using a spectral preconditioner based on the Lanczos method. This paper shows how practical demands of the application dictate the various algorithmic choices that are made in the nonlinear optimization solver, with particular reference to the system in operation at the European Centre for Medium-Range Weather Forecasts.

Probable trajectories associated with the transport of Ochlerotatus albifasciatus during a strong wind event in Buenos Aires city (Argentina)

AbstractBecause of its capacity to infect human beings and domestic animals with a number of different viruses, the study of the mosquito Ochlerotatus albifasciatus (Macquart, 1938, (Diptera: Culicidae)) assumes great importance from the point of view of sanitation. It is a well‐known fact that the abundance of this species peaks after drought periods in the provinces of Buenos Aires and Cordoba. This article aims at explaining the presence of the high abundance of adult O. albifasciatus in Buenos Aires city in February 2005. As no breeding immatures were recorded during the previous weeks, the most likely hypothesis was that mosquitoes entered the city from breeding sites located in the outskirts. Wind observations, the existing knowledge on this species biology, atmospheric dynamic models, and meteorological data were used to support this hypothesis and identify the sources.Mass transport of these individuals was apparently the consequence of a convective process. It was demonstrated that the occurrence of a convective process transported air masses from the periphery towards the City of Buenos Aires. Air‐parcel trajectories, Ezeiza radar images, and the flood zones observed in satellite images indicated that the source was located in the lowlands of Ezeiza in the Rio Matanza basin, some 50 km to the southwest of the City. The evidence suggests that O. albifasciatus is transported by wind, and the trajectory models are a very useful tool to locate the sources of proliferation of these insects. Copyright © 2008 Royal Meteorological Society