[en] We report the discovery of a circumstellar debris disk viewed nearly edge-on and associated with the young, K1 star BD+45° 598 using high-contrast imaging at 2.2 μm obtained at the W.M. Keck Observatory. We detect the disk in scattered light with a peak significance of ∼5σ over three epochs, and our best-fit model of the disk is an almost edge-on ∼70 au ring, with inclination angle ∼87°. Using the NOEMA interferometer at the Plateau de Bure Observatory operating at 1.3 mm, we find resolved continuum emission aligned with the ring structure seen in the 2.2 μm images. We estimate a fractional infrared luminosity of L _IR/L _tot $\simeq <!--\; ???\; -->6_{-<!--\; ???\; -->1}^{+2}$ × 10⁻⁴, higher than that of the debris disk around AU Mic. Several characteristics of BD+45° 598, such as its galactic space motion, placement in a color–magnitude diagram, and strong presence of lithium, are all consistent with its membership in the β Pictoris Moving Group with an age of 23 ± 3 Myr. However, the galactic position for BD+45° 598 is slightly discrepant from previously known members of the β Pictoris Moving Group, possibly indicating an extension of members of this moving group to distances of at least 70 pc. BD+45° 598 appears to be an example from a population of young circumstellar debris systems associated with newly identified members of young moving groups that can be imaged in scattered light, key objects for mapping out the early evolution of planetary systems from ∼10–100 Myr. This target will also be ideal for northern-hemisphere, high-contrast imaging platforms to search for self-luminous, planetary mass companions residing in this system.

[en] The relationship between continental-scale cold air outbreaks (CAOs) in the mid-latitudes and pulse signals in the stratospheric mass circulation in Northern Hemisphere winter (December–February) is investigated using ERA-Interim data for the 32 winters from 1979 to 2011. Pulse signals in the stratospheric mass circulation include “PULSE_TOT”, “PULSE_W1”, and “PULSE_W2” events, defined as a period of stronger meridional mass transport into the polar stratosphere by total flow, wavenumber-1, and wavenumber-2, respectively. Each type of PULSE event occurs on average 4–6 times per winter. A robust relationship is found between two dominant patterns of winter CAOs and PULSE_W1 and PULSE_W2 events. Cold temperature anomalies tend to occur over Eurasia with the other continent anomalously warm during the 2 weeks before the peak dates of PULSE_W1 events, while the opposite temperature anomaly pattern can be found after the peak dates; and during the 1–2 weeks centered on the peak dates of PULSE_W2 events, a higher probability of occurrence of CAOs is found over both continents. These relationships become more robust for PULSE_W1 and PULSE_W2 events of larger peak intensity. PULSE_TOT events are classified into five types, which have a distinct coupling relationship with PULSE_W1 and PULSE_W2 events. The specific pattern of CAOs associated with each type of PULSE_TOT event is found to be a combination of the CAO patterns associated with PULSE_W1 and PULSE_W2 events. The percentage of PULSE_TOT events belonging to the types that are dominated by PULSE_W2 events increases with the peak intensity of PULSE_TOT events. Accordingly, the related CAO pattern is close to that associated with PULSE_W1 for PULSE_TOT events with small-to-medium intensity, but tends to resemble that associated with PULSE_W2 events as the peak intensity of PULSE_TOT events increases.

[en] A crucial problem for partial sky analysis of CMB polarization is the $E$-$B$ leakage problem. Such leakage arises from the presence of 'ambiguous' modes that satisfy properties of both $E$ and $B$ modes. Solving this problem is critical for primordial polarization $B$ mode detection in partial sky CMB polarization experiments. In this work we introduce a new method for reducing the leakage. We demonstrate that if we complement the $E$-mode information outside the observation patch with ancillary data from full-sky CMB observations, we can reduce and even effectively remove the $E$-to-$B$ leakage. For this objective, we produce $E$-mode Stokes $QU$ maps from Wiener filtered full-sky intensity and polarization CMB observations. We use these maps to fill the sky region that is not observed by the ground-based experiment of interest, and thus complement the partial sky Stokes $QU$ maps. Since the $E$-mode information is now available on the full sky we see a significant reduction in the $E$-to-$B$ leakage. We evaluate on simulated data sets the performance of our method for a 'shallow' $f_{\text{sky}}=8\mathrm{\%<!--\; \%\; -->}$, and a 'deep' $f_{\text{sky}}=2\mathrm{\%<!--\; \%\; -->}$ northern hemisphere sky patch, with AliCPT-like properties, and a LSPE-like $f_{\text{sky}}=30\mathrm{\%<!--\; \%\; -->}$ sky patch, by combining those observations with Planck-like full sky polarization maps. We find that our method outperforms the standard and the pure-$B$ method pseudo-$C_{\mathrm{\ell <!--\; ???\; -->}}$ estimators for all of our simulations. Our new method gives unbiased estimates of the $B$-mode power spectrum through-out the entire multipole range with near-optimal pseudo-$C_{\mathrm{\ell <!--\; ???\; -->}}$ errors for $\mathrm{\ell <!--\; ???\; -->}><!--\; >\; -->20$. We also study the application of our method to the CMB-S4 experiment combined with LiteBIRD-like full sky data, and show that using signal-dominated full sky $E$-mode data we can eliminate the $E$-to-$B$ leakage problem.

[en] Sixty-seven unresolved objects with flat blue spectra that had no apparent features on the plates of the Case Low-Dispersion Northern Sky Survey have been observed at higher dispersion and to shorter wavelengths in order to determine their nature. The following classifications are proposed: 20 low-redshift QSOs (z greater than 1.7), two Seyfert 2 galaxies, 23 stars, and two variable objects. The spectra obtained for the remaining 20 objects were flat with no obvious features, but noisy, and these will need further observation. 5 references

No abstract available

[en] Complete text of publication follows. The 25 year TOMS ozone data series (1978 - 2005) in the Northern Hemisphere is investigated with respect to longitudinal and latitudinal dependant trends. Sinusoidal structures in the longitudinal trend behaviour are interpreted in terms of planetary wave activity. This is in agreement with an observed trend in the amplitudes of the planetary waves with zonal wave number 1 and 2. These trends are found to clearly vary with month and latitude. This effect is used to separate chemically and dynamically induced ozone trends. It is discussed how the background ozone concentration in midlatitudes might be influenced by streamer events caused by breaking planetary waves.

[en] Aircraft produce condensation trails, which are thought to increase high-level cloudiness under certain conditions. However the magnitude of such an effect and whether this contributes substantially to the radiative forcing due to the aviation sector remain uncertain. The very substantial, near-global reduction in air traffic in response to the COVID-19 outbreak offers an unprecedented opportunity to identify the anthropogenic contribution to the observed cirrus coverage and thickness. Here we show, using an analysis of satellite observations for the period March–May 2020, that in the 20% of the Northern Hemisphere mid-latitudes with the largest air traffic reduction, cirrus fraction was reduced by ∼9 ± 1.5% on average, and cirrus emissivity was reduced by ∼2 ± 5% relative to what they should have been with normal air traffic. The changes are corroborated by a consistent estimate based on linear trends over the period 2011–2019. The change in cirrus translates to a global radiative forcing of 61 ± 39 mW m⁻². This estimate is somewhat smaller than previous assessments. (letter)

[en] Complete text of publication follows. This paper will present results of the analysis of the ionospheric F layer peak parameters variability under quiet and stormy conditions over middle latitudes. The analysis was carried out using manually checked hourly foF2 and hmF2 values obtained from selected ionospheric stations of the Northern (NH) and Southern hemisphere (SH). The observations were compared with the IRI2007 model outputs. Quality of the STORM model storm-time corrections was also evaluated. Overall summary of the evaluation results for Northern hemisphere indicates the decreasing ability of the model to simulate storm-time foF2 behaviour with decreasing latitude. For Southern hemisphere an efficiency of the model corrections seems to be considerably lower and decreases with increasing latitude. In general, the quiet time hmF2 above NH middle latitudes is better represented by IRI during winter and summer months, while at SH middle latitudes the model simulates hmF2 variability more successfully during summer and equinoxes. Our results indicate an importance of knowledge of the local patterns of ionospheric variability for the development of global models.

[en] Through their modifications of channels and floodplains, beavers are a premier example of ecosystem engineers. Historical and stratigraphic records suggest that hundreds of millions of beavers once modified small to medium rivers throughout the northern hemisphere. Where beavers actively modify the channel and floodplain with dams, ponds, and canals, their activities increase habitat abundance and diversity, biodiversity, nutrient uptake, attenuation of downstream fluxes of water and sediment, and resilience of the river corridor to disturbances. Loss of beavers through commercial trapping and habitat modification occurred simultaneously with other human modifications of uplands and river corridors. The cumulative effects of these human modifications have been to greatly reduce the ecosystem services provided by rivers. Contemporary efforts to re-introduce beavers in North America and Eurasia and to mimic the effects of beaver engineering with beaver dam analogues and Stage 0 restoration represent a good start, but fundamental questions remain about the extent of such restoration efforts needed to create and maintain significant increases in riverine functions. (paper)

[en] Before the present time disturbed state the stratospheric ozone layer over the northern hemisphere usually demonstrated three regions of high total ozone values. Estonia belonged to one of these regions. The reliable data about the geographical distribution of total ozone exist since 1957. Extrapolating them back we can speculate that our biosphere has been better protected from the ultraviolet irradiation than most part of the same latitude. A short review of the key moments of the total ozone research history has been presented. Except the chemical loss during polar spring the total ozone values are dependent on stratospheric synoptic scale motions. Negative ozone anomalies tend to coincide with low pressure in stratosphere (tropospheric highs) and vice versa. On the mean heights of the ozone layer the tropical air, the mid latitude air and the air inside the winter polar vortex are strongly isolated. The exchange through these strong wind barriers is possible only in the form of thin filaments or air tongues. Those filaments of ozone poor air from tropical latitudes are the main reason of ozone mini holes during most part of year. The results of total ozone variations in 1994-1996 have been discussed. In all cases the values in spring often are below the undisturbed latitude mean. In summer the results are close to the mean but especially in summer 1995 several synoptic scale mini holes were recorded (author)