Asteroid’s name after Vladis Vujnović

According to the International Astronomical Union, Asteroid 182590 got the name after Professor Vladis Vujnović

Detection of climatic fluctuations by Hilbert-Huang method in the data of Zagreb-Grič centennial observatory, Croatia

Advanced statistical methods are applied on long-term data sets from Zagreb-Grič centennial observatory in Croatia to address recent climate change and variabilities; annual averages are used. Hilbert-Huang transform (HHT), consisting of empirical mode decomposi- tion (EMD) and Hilbert spectral analysis (HSA), is an empirically based data-analysis method for extracting periodic components embedded within generally nonlinear and non-stationary data. The EMD splits the original series into a so-called intrinsic mode functions (IMFs). First, using the EMD algorithm, intrinsic mode functions (IMFs) are obtained. The analysis of low frequency IMFs indicates significant influence of the North-Atlantic Oscillation on the air temperature, cloudiness and precipitation series in the part of northern Croatia. For the con- sidered climatic elements, the analysis revealed mild deviations in natural fluctuations of the analyzed signal for the last 30 to 40 years, which are most likely caused by anthropogenic activi- ties. Next, HSA is applied to each IMF obtained for the series of annual averages of sea level air pressure. In order to validate this approach and the results, an associated Hilbert spectrum (HS) is compared with the continuous wavelet analysis, i.e., this is another corresponding checkup. The comparison shows significantly improved time and frequency resolution in favor of HS. Moreover, HS provides a unique capability of displaying intra-wave frequency modula- tion, i.e., changes in frequency that occur within one cycle of oscillation

A preliminary case study of the possible Adriatic tropical-like cyclone from the 21st of January 2023

This short article addresses a preliminary study of transient subsynoptic cyclonic behavior over a broader area of the Adriatic Sea. The January 2023 case presented here shows a transition from an extratropical Mediterranean cyclone into a partially tropical-like cyclonic system (TLC) over the south and central Adriatic Sea. The warm barotropic core, cyclonic “eye” and relatively symmetric precipitation bands around the vortex were the main TLC properties of this system. In the short analysis of the event, the assumption is made that size limitations of the Adriatic basin prevented development of the system into a full-strength “medicane”. Hence, such vigorous small-scale cyclones just might be named “adricanes”. Presentation of this case contributes to the relatively scarce research of these rare Adriatic TLC events. The criteria for cyclonic system classification as TLC or extra- tropical are also discussed, with the supporting idea of a spectrum between fully tropical and fully extratropical cyclones (instead of binary classification), where the particular system can fall anywhere in between, depending on the ratio of tropical and extratropical properties it possesses

SEA-SURFACE TEMPERATURE EFFECTS ON 3D BURA FLOW

A nonhydrostatic numerical model with a higher order turbulence closure scheme is used to study the effect of the sea surface temperature (SST) on the nonlinear flow over a mountain in the presence of rotation. The low-level jet that develops on both flanks of the mountain is intensified by the Coriolis effect on the northern flank. Shooting flow develops down the slope ending over the sea while resembling a hydraulic jump. This is considered as bura like flow. Three different cases are addressed, the control run and two cases with the SST 10K colder, and 10K warmer than the control run. The maximum wind speeds that occur are around two times higher than the background wind speeds. Varying the SST induces changes to the flow that affect the position of the hydraulic jump and the extent and intensity of low-level jets that form on both flanks of the mountain. A hydraulic jump is modulated by orographicaly generated eddies

A CURVATURE EFFECT ON THE CRITICAL RICHARDSON NUMBER

Transitions from laminar to turbulent flow associated with a critical level in the stratified shear flow are related to the critical (gradient) Richardson number, Ric, the minimum value of which is Ric ≈ 1/4. Based on the linear theory and a modified Taylor-Goldstein equation, here it is plausibly shown that Ric may slightly vary from this value if the mean wind speed profile contains a small curvature (parameterized here) around the critical level. The modified Ric that depends on the dimensionless curvature α ≡ (U’’ζ/U’) is Ric(α) = (1 + α/2)[α + (1 + α/2)/4]

Sergej Sergejevich Zilitinkevich (4.1936 - 2.2021)

Sergej Sergejevich Zilitinkevich - In memoriamSergej Sergejevich Zilitinkevich - In memoria

KATABATIC FLOW WITH CORIOLIS EFFECT

Abstract Katabatic flows on long glaciers in high latitudes experience the Coriolis effect deflecting the flow thus affecting turbulent transports in the boundary layer. Analytically katabatic flows have been best represented by Prandtl model. However, the classic Prandtl model does not take into account the effect of the Coriolis force. It is found that after a straightforward inclusion of this effect, the solution to the model is correct only up to a constant, and does not simultaneously satisfy all boundary conditions. Therefore, a modified analytic Prandtl model is examined. The modified approximate solution agrees with a numerical solution, and qualitatively, with the results of other related studies. Besides a theoretical significance, our approximate analytic solution can be useful for developing a better parameterization in climate models having a poor vertical resolution for such shallow but persistent flows

Internal wave drag in stratified flow over mountains on a beta plane

The impact of the variation of the Coriolis parameter f on the drag exerted by internal Rossby-gravity waves on elliptical mountains is evaluated using linear theory, assuming constant wind and static stability and a beta-plane approximation. Previous calculations of inertia-gravity wave drag are thus extended in an attempt to establish a connection with existing studies on planetary wave drag, developed primarily for fluids topped by a rigid lid. It is found that the internal wave drag for zonal westerly flow strongly increases relative to that given by the calculation where f is assumed to be a constant, particularly at high latitudes and for mountains aligned meridionally. Drag increases with mountain width for sufficiently wide mountains, reaching values much larger than those valid in the non-rotating limit. This occurs because the drag receives contributions from a low wavenumber range, controlled by the beta effect, which accounts for the drag amplification found here. This drag amplification is shown to be considerable for idealized analogues of real mountain ranges, such as the Himalayas and the Rocky mountains, and comparable to the barotropic Rossby wave drag addressed in previous studies

Internal wave drag in stratified flow over mountains on a beta plane

The impact of the variation of the Coriolis parameter f on the drag exerted by internal Rossby-gravity waves on elliptical mountains is evaluated using linear theory, assuming constant wind and static stability and a beta-plane approximation. Previous calculations of inertia-gravity wave drag are thus extended in an attempt to establish a connection with existing studies on planetary wave drag, developed primarily for fluids topped by a rigid lid. It is found that the internal wave drag for zonal westerly flow strongly increases relative to that given by the calculation where f is assumed to be a constant, particularly at high latitudes and for mountains aligned meridionally. Drag increases with mountain width for sufficiently wide mountains, reaching values much larger than those valid in the non-rotating limit. This occurs because the drag receives contributions from a low wavenumber range, controlled by the beta effect, which accounts for the drag amplification found here. This drag amplification is shown to be considerable for idealized analogues of real mountain ranges, such as the Himalayas and the Rocky mountains, and comparable to the barotropic Rossby wave drag addressed in previous studies