Geofisica pura e applicata

Die Schwächung der Globalstrahlung, die zu irgendeiner Zeit an irgendeinem Orte beobachtet wurde, muß fast ausschließlich auf das Konto der Wolken, also des in der Luft befindlichen flüssigen Wassers gesetzt werden. In der vorliegenden Arbeit wird versucht, eine Meßgröße zu definieren, die die Wirkung dieses Wolkenwassers ausdrückt. Sie wird «optische Wolkendichte» genannt und ist identisch mit dem bereits vonTrabert vor 60 Jahren als maßgebend für die Sicht in Wolken erkannten Quotienten aus Wassergehalt und Tropfendurchmesser. Ein Verfahren für die Berechnung der optischen Wolkendichte wird angegeben. Zugrunde gelegt wird eine Zerstreuungsformel, die der Verfasser vor 25 Jahren aufstellte. Ein Übergang zu neueren Zerstreuungsformeln ist ohne weiteres möglich, wenn sie sich als besser erweisen sollten. In der Arbeit werden die vollständigen stündlichen Werte der optischen Wolkendichte für einen Winter-und einen Sommermonat an der Station Melbourne-Box Hill und einen Dezember an der Station Darwin wiedergegeben. An der ersteren Station wurde ein linearer Zusammenhang zwischen den Monatsmitteln der optischen Wolkendichte und den Monatssummen des Niederschlages festgestellt. Die Monatsmittel der und den Monatssummen des Niederschlages festgestellt. Die Monatsmittel der optischen Wolkendichte an den Tropenstationen Darwin und Rabaul, wurden bei gleichen Niederschlagssummen um etwa die Hälfte niedriger gefunden als in Box Hill. Dies läßt auf größere Tropfendurchmesser in den Tropen schließen. Der Zusammenhang zwischen Niederschlagsdichte und optischer Wolkendichte wurde für einen Monat in Box Hill untersucht. Es wurde gefunden, daß Niederschläge gelegentlich auch bei ziemlich kleinen optischen Wolkendichten eintreten könne. Um weitere Schlüsseauf die Struktur der regnenden Wolken zu ziehen, muß eine genauere Untersuchung der Niederschlagsfelder um die Station ausgeführt werden. Eine Trennung derTrabertschen Meßgröße in Wolkenwassergehalt und Tropfengröße war schon seit langem durch Infrarotmessungen der Strahlung unter Wolken geplant. Behandelt wird eine Meßreihe im September und Oktober 1942 in Potsdam. Gemessen wurde im langwelligen Ultraviolett, im äußersten Rot und in vier Infrarotgebieten. Die Mittel der prozentualen Durchlässigkeiten in den verschiedenen Spektralgebieten wurden für die Beobachtungen bei klarem Himmel, bei leichter vollständiger Himmelsbedeckung und bei dichten Wolken gebildet. Die Absorption der Wolken wurde viel stärker gefunden als nach ihren vermutlichen Wassergehalten zu erwarten war. Dieser Effekt wurde auf eine Vervielfachung des Lichtweges in der Wolke durch die Zerstreuungvorgänge zurückgeführt. Besonders stark war der Strahlungsverlust im Spektralgebiet um 1.3μ. Es wurde versucht, die Tropfengröße in den Wolken durch Bestimmung der Lage dieses Absorptionsmaximums zu bestimmen. Die erhaltenen mittleren Tropfendurchmesser liegen bei 2.5μ. Die Weiterführung der Beobachtungen wurde durch Krankheit des Verfassers unterbrochen. Auf ihre Wichtigkeit wird hingewiesen und die dazu erforderlichen Apparaturen beschrieben.

In this study, we aimed to analyze the role of air–sea coupling with one-dimensional (1D) and 3D ocean coupled models in simulating the monsoon depression (MD) that formed over the Bay of Bengal from 13 to 17 August 2018. This synoptic system produced substantial heavy rainfall amounts over the east and west coasts of India, which led to a flooding situation along its path. In view of its characteristic features, we considered this MD as an ideal case and conducted six numerical simulations. The first three experiments were initialized by GFS data using a stand-alone Weather Research and Forecasting model (WRFCNTRL) coupled with its 1D ocean mixed layer (OML) model (OMLCNTRL) and 3D Price–Weller–Pinkel (PWP) ocean model (PWPCNTRL). The other three experiments (WRF3DVAR, OML3DVAR, and PWP3DVAR) were conducted with the same set of models by assimilating all available observations using the 3D variational data assimilation (3DVAR) method. The evaluation of results of coupled model simulations with observed estimates clearly suggested that the WRF model enabling ocean surface feedback has a positive impact on the simulation of MD and associated heavy rainfall. These improvements were mainly seen in the simulated tracks of the coupled model experiment, which were found to be in the order of 23–29% and 31–38% with OMLCNTRL and PWPCNTRL, respectively, as compared with WRFCNTRL at 48–72 forecast hours. The improvements were significant with the ocean coupled models and assimilation of observations, suggesting an overall reduction in the track error of about 13–17%, 27–32%, and 37–44% with WRF3DVAR, OML3DVAR, and PWP3DVAR, respectively, as compared with WRFCNTRL at 48–72 forecast hours. The positive impact of observational assimilation and ocean coupling could be due to the improved simulation of the depression-induced ocean surface variations, enhanced sea surface cooling, and increased surface enthalpy flux, leading to the changes in dynamical fields and the moisture convergence process. Our analysis suggests that the WRF-PWP model with assimilation of available observations provides improved estimates of the track and intensity of the MD over the Bay of Bengal and its associated heavy rainfall.

Geomagnetic field variations recorded by an array of magnetometers spread across the Kachchh Rift basin are reduced to a set of induction arrows as a diagnostic of lateral electrical conductivity variations. A non-uniform thin-sheet electrical conductance model is developed to account for the salient induction patterns. It indicates that the imaged conductivity anomalies can be related to the sediment-filled structural lows in between the fault bounded uplifts. It is suggested that sagging structural lows preserved the marine sediments deposited during the Mesozoic sea transgression and later developed into first order embayment basins for the deposition of sediments in association with Late Eocene transgression. Depth integrated electrical conductance helped in mapping two depo-centres: along the ENE-WSW trending Banni half-Graben bounded by the Kachchh Main fault on the south and, second, along the Vinjan depression formed in response to the subsidence between the Vigodi fault and westward extension of the Katrol Hill fault together with the westward bending of the Median High. Presence of metamorphosed graphite schist clasts in shale dominated Mesozoic sequence and/or thin films of carbon resulting from the thermal influence of Deccan activity on Carbonate-rich formations can account for the high electrical conductivity anomalies seen in the depo-centres of thick Mesozoic and Tertiary sediments. Additionally two high conductivity zones are imaged encompassing a block defined by the 2001 Bhuj earthquake and its aftershocks. In agreement with gravity, magnetic and seismic velocity signatures, aqueous fluids released by recrystallizing magmatic bodies intruded in association with Deccan trap activity account for mapped high conductivity zones. High fluid pressure in such a fractured domain, surrounding the intruded magmatic plugs, perturb the regional stress concentrations to produce frequent and low magnitude aftershocks in the shallow section of the epicentral track of the 2001 Bhuj earthquake.

The relationship between the phonon conductivity at room temperature (K N ) and the seismic parameter (Φ) for silicate minerals is suggested. The considerations are based on the Debye model of thermal energy transport phenomena in solids and on the ‘seismic equation of state’ for silicates and oxides given byAnderson (1967). The semiempirical relationship is the formK N = 0.43Φ0.82 where Φ is in km2/s2 andK N in mcal/cm s K, and the empirical relationship isK N =(0.528±0.006)Φ −(8.18±2.11). The laboratory data on thermal and elastic properties for several silicates were taken fromHorai andSimmons (1970).

This study investigates the relationship between Indian summer monsoon (ISM) rainfall and the Atlantic Multidecadal Oscillation (AMO) on a monthly and seasonal basis with respect to the quasi-biennial oscillation (QBO) during the period 1953–2016. The analysis is performed for full time series of monthly and seasonal ISM rainfall and AMO index data as well by regrouping according to the westerly and easterly phase of the QBO (at 50 hPa). A direct positive association is observed between ISM rainfall and the AMO for the full time series during the pre-monsoon (March–April–May) and winter (January–February) seasons via the Rossby wave train from the North Atlantic across South Asia, thus resulting in an increase in the temperature gradient between the Indian Ocean (IO) and Eurasia which strengthened the ISM. The strongest association was found during the pre-monsoon season and especially during April. The variability in ISM rainfall was more prominently modulated by the pre-monsoon warm phase of the AMO along with the westerly phase of the QBO as compared with the easterly phase. The elevated ISM rainfall during the warm AMO phase and westerly phase of the QBO ultimately triggered low IO sea surface temperature and salinity during September–October.

Several experiments were undertaken at Kolkata (latitude: 22°34′N, longitude: 88°30′E) on the solar eclipse day of August 1, 2008 to observe the effects of the solar eclipse on Fair Weather Field (FWF) and VLF amplitude and phase. The experimental results presented here show significant deviations of the observed parameters from their normal values, as they are determined by the average of the records obtained on 5 days adjacent to the day of the solar eclipse.

Properties of seismoelectric waves in relation to natural earthquakes have been investigated. The electromagnetic disturbances were analyzed to test the hypothesis that pulse-like electric variations are directly related to microcracks as source. Because variation is very difficult to detect, there have been few quantitative field investigations. We used selected events with clear S and P phases from the data catalog obtained before the Tohoku earthquake in 2011. The electric strength of the fast P wave (P f), S wave (S), and electromagnetic wave (EM) associated with formation of cracks of tensile mode were estimated. The co-seismic electric signal accompanied by the S wave has the largest strength, well above the noise level, and the EM wave has the lowest strength. Analytical estimation of the ratio of the strengths of the Pf and EM phases to that of the S phase by use of Pride’s equations gave results partially in agreement with observation (the order was Apf > A s > A em). The strength of the observed electromagnetic mode is approximately two orders of magnitude larger than that estimated from the theory. We suggest this greater strength can be attributed to the converted modes at layer contracts or to the effect of the boundary between free atmosphere and crust. Overall agreement between observations and theoretical estimates suggests that electromagnetic anomalies, crustal deformation, and groundwater changes can be investigated on the basis of the unified equations for the coupled electromagnetics, acoustics, and hydrodynamics of porous media.