Association between mid-latitude circulation and Indian monsoon rainfall

The statistical relationship between the summer monsoon rainfall over India and mid-latitude general calculation at the 500 hPa level was investigated for the period 1971-1989. The index used to characterise general circulation feature is the perturbation of the zonal flow (ratio of meridional to zonal index) for the latitudinal band 35°N - 70°N over different geographical area and the hemisphere. It was found that the perturbation of the zonal flow during preceding January over the geographical sector 1 (45°W - 90°E) shows significant relationship with the subsequent Indian summer monsoon rainfall in an inverse manner. Thus, the perturbation of the mid-latitude circulation during preceding January over the geographical sector seems to be a useful predictor of the subsequent Indian monsoon rainfall. Significant simultaneous inverse relationship also exists between perturbation of mid-latitude zonal flow during July to September over Sector 2 (90°E- 160°W) and summer monsoon rainfall over northwest India.

Analysis of total ozone, potential vorticity and tropopause pressure over southeast Asia during winter

This article shows the analysis of total ozone and potential vorticity and also tropopause pressure during winter period (December, January and February) over the area 20°-50°N, 90°.160oE (southeast Asia), This is done for three different latitude bands 20o-30oN, 30° -40° N and 40°S -50oN. Due to maximum, latitudinal gradient of ozone in the lower latitudinal band, high correlation is found with potential vorticity and also with tropopause level

Peninsular effect on species richness in Italian small mammals and bats

Peninsular effect is an anomalous gradient in plant and animal species richness from base to tip of a given peninsula. This pattern has been studied intensely on various taxonomic groups, but with scarce attention for using standardized data. Here, using presence-absence data normalized by the field effort, the peninsular effect on the species richness of some mammalian groups (Eulipotyphla [i.e. Soricomorpha + Erinaceomorpha], Rodentia, and Chiroptera) was analyzed along the Italian peninsula. Specifically, species richness at each 30′-wide latitudinal band and the normalized species richness were compared, and generalized linear models (GLM) were used to assess whether habitat diversity, altitudinal range and area of each latitudinal band were the main predictors in explaining the peninsular effects in each of the three mammalian orders. In both Rodentia and Chiroptera, species richness was better predicted by habitat heterogeneity and by the interaction term habitat heterogeneity × field effort. For Eulipotyphla, GLM models gave no significant results. Our study highlighted the importance of taking into account the sampling effort in order to proper evaluate the peninsular effects on species richness in animals.

Solar cycle variation of simple and complex active regions

<p>Solar active regions (ARs) emerge on the Sun’s photosphere and they frequently produce flares and coronal mass ejections which are among major space weather drivers. Therefore, studying ARs can improve space weather forecast.</p><p>The Mount Wilson Classification has been used since 1919 in order to group groups ARs according to their magnetic structures. In this study, we investigated the magnetic classification of 4797 ARs and their cyclic variation, using our daily approach for the period of January 1996 to December 2018.</p><p>We show that the monthly number of the simple ARs (SARs) attained their maximum during first peak of the solar cycle, whereas more complex ARs (CARs) reached their maximum roughly two years later, during the second peak of the cycle. We also demonstrate that the total abundance of CARs is very similar during a period of four years around their maximum number. We also studied the latitudinal distributions of SARs and CAR in northern and southern solar hemispheres and show that the independent of the complexity type, the distributions are the same in both hemispheres.</p><p>Furthermore, we investigated the earlier claim of increase in number of CARs due to the decrease in ARs latitudinal band. Here we show that, contrary to this claim, CARs attained their maximum number before the latitudinal band started to decrease in both northern and southern hemispheres.</p>

Fluctuation of recent large impact craters rate on Mars from automatic crater detection

<p>Knowledge of collision rates through time and space is essential because meteoritic impact crater counting is the only way to determine the ages of surface geological units and processes on the solid bodies of our Solar System. All chronology models assume a constant size distribution of impactors and an exponential decay of the impact flux between 4 Ga and 2.5 Ga before the present followed by a constant rate over the last 2.5 Ga. These two assumptions are challenged by recent evidence for an increase of the impact flux on the Moon and the Earth and probably on Mars associated with a decoupling between the flux of small and large impactors over the last billion years. Here, using the results of an automatic crater detection algorithm, we investigate the evolution of the rate of formation of large impact craters (Dc ≥ 20km) on Mars and thus infer the evolution of the flux of large impactors (Di > 5km) from the size-frequency distribution of small craters superposed to the ejecta blankets of large ones.</p><p>The dating of large impact craters on Mars is limited by several factors such as the degradation of ejecta blankets and the retention rate of small craters superposed to their ejecta. We therefore focused on craters ≥20km in diameter exhibiting an ejecta blanket according to the crater database and located on a latitudinal band between ±35°. We then selected those whom their ejecta are not affected by volcanic/tectonic processes or by the formation of another large nearby impact crater. The final set includes 590 impact craters.</p><p>If one can argue the impact flux cannot be fully recorded for the last 4Ga due to resurfacing processes erasing progressively the ejecta blanket and large craters themselves, Hesperian and Noachian terrains within the 35° latitudinal band should nevertheless have retained all D≥20km craters over a portion of the Amazonian period. The CSFD of craters younger than 600Ma (113 craters) superposed to these terrains is consistent with the 600Ma isochron, supporting the fact that the entire population of craters ≥20km formed over the last 600 million years on this portion of the Martian surface has been counted completely. We therefore focused on the analysis of the impact rate evolution over this range of time from this crater sub-sample.</p><p>The formation of large impact craters is not homogeneously distributed over the time range investigated here. Our data suggest an inconsistency between the flux used to date each crater and the rate inferred from these datings, thus implying that the small and large body impact fluxes are decoupled from one another. We note also sharp peaks centered around 480, 280 and 100Ma. Preliminary statistical test show that 280Ma peak is marginally significant whereas the two others are too small to be statistically significant. This pattern would be consistent with other independent arguments for increased rate with similar intensity and timing on the Moon and Mars for which the causes are probably collisions and potentially formation of asteroid families within the main asteroid belt.</p>

New Type of Storm Spotted on Saturn

In 2018, four massive storms formed near the planet’s north pole, interacting with each other and affecting a full latitudinal band.

The Summertime Diurnal Cycle of Precipitation Derived from IMERG

The Integrated Multi-satellitE Retrievals for GPM (IMERG) precipitation product derived from the Global Precipitation Measurement (GPM) constellation offers a unique opportunity of observing the diurnal cycle of precipitation in the latitudinal band 60 ° N–S at unprecedented 0.1 ° × 0.1 ° and half-hour resolution. The diurnal cycles of occurrence, intensity and accumulation are determined using four years of data at 2 ° × 2 ° resolution; this study focusses on summertime months when the diurnal cycle shows stronger features. Harmonics are fitted to the diurnal cycle using a non-linear least squares method weighted by random errors. Results suggest that mean-to-peak amplitudes for the diurnal cycles of occurrence and accumulation are greater over land (generally larger than 25% of the diurnal mean), where the diurnal harmonic dominates and peaks at ~16–24 LST, than over ocean (generally smaller than 25%), where the diurnal and semi-diurnal harmonics contribute comparably. Over ocean, the diurnal harmonic peaks at ~0–10 LST (~8–15 LST) over open waters (coastal waters). For intensity, amplitudes of the diurnal and semi-diurnal harmonics are generally comparable everywhere (~15–35%) with the diurnal harmonic peaking at ~20–4 LST (~3–12 LST) over land (ocean), and the semi-diurnal harmonic maximises at ~5–8 LST and 17–20 LST. The diurnal cycle of accumulation is dictated by occurrence as opposed to intensity.

Decrease in tropospheric O₃ levels in the Northern Hemisphere observed by IASI

In this study, we describe the recent changes in the tropospheric ozone (O3) columns measured by the Infrared Atmospheric Sounding Interferometer (IASI), onboard the Metop satellite, during the first 9 years of operation (January 2008 to May 2017). Using appropriate multivariate regression methods, we differentiate significant linear trends from other sources of O3 variations captured by IASI. The geographical patterns of the adjusted O3 trends are provided and discussed on the global scale. Given the large contribution of the natural variability in comparison with that of the trend (25–85 % vs. 15–50 %, respectively) to the total O3 variations, we estimate that additional years of IASI measurements are generally required to detect the estimated O3 trends with high precision. Globally, additional 6 months to 6 years of measurements, depending on the regions and the seasons, are needed to detect a trend of |5| DU decade−1. An exception is interestingly found during summer at mid- and high latitudes of the Northern Hemisphere (NH; ∼ 40 to ∼ 75∘ N), where the large absolute fitted trend values (∼ |0.5| DU yr−1 on average) combined with the small model residuals (∼ 10 %) allow for detection of a band-like pattern of significant negative trends. Despite no consensus in terms of tropospheric O3 trends having been reached from the available independent datasets (UV or IR satellites, O3 sondes, aircrafts, ground-based measurements, etc.) for the reasons that are discussed in the text, this finding is consistent with the reported decrease in O3 precursor emissions in recent years, especially in Europe and USA. The influence of continental pollution on that latitudinal band is further investigated and supported by the analysis of the O3–CO relationship (in terms of correlation coefficient, regression slope and covariance) that we found to be the strongest at northern midlatitudes in summer.

Decrease in tropospheric O₃ levels of the Northern Hemisphere observed by IASI

In this study, we describe the recent changes in the tropospheric ozone (O3) columns (TOCs) measured by the Infrared Atmospheric Sounding Interferometer (IASI) onboard the Metop satellite during the first 9 years of the IASI operation (January 2008 to May 2017). Using appropriate multivariate regression methods, we discriminate significant linear trends from other sources of O3 variations captured by IASI. The geographical patterns of the adjusted O3 trends are provided and discussed on the global scale. Given the large contribution of the natural variability in comparison with that of the trend (25–85 % vs 15–50 %, respectively) to the total O3 variations, we estimate that additional years of IASI measurements are generally required to detect the estimated O3 trends with a high precision. Globally, additional 6 months to 6 years of measurements, depending on the regions and the seasons, are needed to detect a trend of |5| DU/decade. An exception is interestingly found during summer in the mid-high latitudes of the North Hemisphere (N.H.; ~ 40° N–75° N) where the large absolute fitted trend values (~ |0.5| DU/yr on average) combined with the small model residuals (~ 10 %) allow the detection of a band-like pattern of significant negative trends. This finding supports the reported decrease in O3 precursor emissions in recent years, especially in Europe and US. The influence of continental pollution on that latitudinal band is further investigated and supported by the analysis of the O3–CO relationship (in terms of correlation coefficient, regression slope and covariance) that we found to be the strongest at the northern mid-latitudes in summer.