The early months of 2020 showed record-breaking levels of aerosol optical depth (AOD) over the Southern Hemisphere (SH). Apart from the tropics, monthly AOD values over most of the SH exceeded the average by more than three standard deviations. This anomalous AOD is attributed to a combination of the intensity and location of the Australian bushfires. The fires took place south enough, where the tropopause altitude is relatively low, within the mid-latitude cyclone belt. This location allowed for deep convection over and downwind of the fires, which transported the smoke to the stratosphere, where its lifetime is an order of magnitude longer than it would have been in the lower atmosphere. The lower bound of the stratospheric smoke mass in January 2020 was ~2.1 ± 1 teragrams, which lead to cooling by more than 1.0 ± 0.6 watts per square meter over cloud-free oceanic areas.
E. Hirsch Armament Development Authority, P. 0. BOX 2250, Haifa (Israel) Verbesserte Fomeln fiir die Geschwindigkeit, Beschleunigung und den Projektionswinkel von explosiv beschleunigten Liners Verbesserte eindimensionale Formeln sowohl fur die Richtung als such fur die GroBe der Geschwindigkeit von explosiv beschleunigten Liners werden entwickelt. Zuerst wird eine analytische Formel fur die Bewegungsrichtung des Liners unter veranderlichen Bedingungen abgeleitet. Diese neue Formel wird verglichen sowohl mit zweidimensionalen Berechnungen als auch mit experimentellen Daten und zwar fur Hohlladungs-und explodierende Zylindergeometrien. Die neue Formel ist genauer als es die klassische stationare Taylor-Winkelfor-me1 fur diese Falle ist. Weiterhin wird fur implosive Geometrien eine neue Formel aufgestellt fir die voll beschleunigte Linergeschwindigkeit. Da die Standard-Gurney-Naherung nicht auf implodierte Geometrien anwendbar ist, wird eine modifizierte Naherung angenommen. Die Ergebnisse stimmen gut mit den Resultaten des zweidimensionalen Rechenprogramms fur einen weiten Sprengstoff-und Geometriebereich uberein. AuRerdem wird gezeigt, daR die Geschwindigkeits-Historie einem Exponentialgesetz folgt, und es wird eine brauchbare Formel fur die charakteristische Metallbeschleunigungszeit entwickelt. Formules amkliorees pour le calcul de la vitesse, de I'acceleration et de I'angle de rekvement des revetements projetCs par explosif On a mis au point des formules monodimensionnelles amkliortes pour calculer la direction et la grandeur du vecteur vitesse de revCtements projetCs plar explosif. En premier lieu on Ctablit une expression analytique qui donne la direction du vecteur vitesse du revktement pour diffkrentes conditions de projection. Cette nouvelle formule est comparte aux rCsultats des calculs bidimensionnels et aux donnCes exptrimentales obtenues avec des charges cremes et des charges cylindriques. La nouvelle formule fournit pour ces cas des rCsultats plus precis que la formule classique de Taylor pour 1'Ctat stationnaire.En outre on indique une nouvelle formule pour les gComCtries implosives qui fournit la vitesse du revCtement a pleine accCltration. L'approximation classique de Gurney ne s'appliquant pas aux gComCtries implosives, on adopte une approximation modifike. Les rksultats concordent bien avec ceux du code de calcul bidimensionnel pour une large gamme d'explosifs et de gtomktries. On montre Cgalement que l'holution temporelle de la vitesse suit une loi exponentielle et on dtveloppe une formule pratique pour calcuculer le temps d'acdlkration caractkristique des m6taux. SummaryImproved one-dimensional formulas for both the direction and magnitude of the velocity of explosively driven liners are developed. First, an analytical formula for the direction of motion of the liner under unsteady conditions is derived. This new formula is compared withboth two-dimensional calculations and experimental data for both shaped-charge and exploding cylinder geometries. The new formula is more accurate than the cla...
Abstract.A recent field campaign was conducted to measure the properties of thin, warm convective clouds forming under conditions of weak updrafts. During the campaign, shortlived clouds (on the order of minutes) with droplets' effective radius of 1-2 µm and low liquid water path (∼ 500 mg m −2 ) were measured. These low values are puzzling, since in most studies an effective radius of 4 µm is reported to serve as the lower bound for clouds. A theoretical cloud model designed to resolve the droplet-activation process suggested conditions that favor the formation of such clouds. Here we show that these clouds, which mark the transition from haze to cloud, are highly sensitive to the magnitude of the initial perturbation that initiated them. We define these clouds as "transition-zone clouds". The existence of such clouds poses a key challenge for the analysis of atmospheric observations and models, since they "further smooth" the transition from dry aerosol through haze pockets to cumulus clouds.
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