On the interpretation of low-latitude hydrological proxy records based on Maunder Minimum AOGCM simulations

An increasing number of proxy records, which are related to changes in the hydrological cycle, have been collected for climate reconstructions of the last millennium. There has been, however, little attempt to test climate models with such proxy records or to interpret proxy records using climate model simulations. In the present study, we analyze the hydrological changes between three different types of experiments: a present-day control, a perpetual AD 1640, and an ensemble of six transient Maunder Minimum (AD 1640-1715) simulations. Atmospheric moisture transport is investigated in terms of contributions of specific humidity and circulation changes. The study points out the importance of the specific humidity contribution to changes in moisture transport reflected in hydrological proxy records. The moisture budget of the western tropical Pacific is also investigated to aid the interpretation of a proxy record in this specific region. The present-day freshening of the western tropical Pacific, compared to the Maunder Minimum, is explained by the increased zonal moisture transport via trade winds, mainly due to the increased amount of atmospheric water vapor content in the warming world. Due to the existence of several uncertainty factors, such as forcing reconstructions, the link between the model simulations and proxy records is, however, not definitive, but the thermal contribution to hydrological proxy records is important and not limited to the Maunder Minimum perio

Externally forced and internal variability in ensemble climate simulations of the Maunder Minimum

© 2005 American Meteorological Society (https://www.ametsoc.org/ams/index.cfm/publications/ethical-guidelines-and-ams-policies/ams-copyright-policy/

Simulated decadal oscillations of the Atlantic meridional overturning circulation in a cold climate state

The significance of the Atlantic meridional overturning circulation (MOC) for regional and hemispheric climate change requires a complete understanding using fully coupled climate models. Here we present a persistent, decadal oscillation in a coupled atmosphere-ocean general circulation model. While the present study is limited by the lack of comparisons with paleo-proxy records, the purpose is to reveal a new theoretically interesting solution found in the fully-coupled climate model. The model exhibits two multi-century-long stable states with one dominated by decadal MOC oscillations. The oscillations involve an interaction between anomalous advective transport of salt and surface density in the North Atlantic subpolar gyre. Their time scale is fundamentally determined by the advection. In addition, there is a link between the MOC oscillations and North Atlantic Oscillation (NAO)-like sea level pressure anomalies. The analysis suggests an interaction between the NAO and an anomalous subpolar gyre circulation in which sea ice near and south of the Labrador Sea plays an important role in generating a large local thermal anomaly and a meridional temperature gradient. The latter induces a positive feedback via synoptic eddy activity in the atmosphere. In addition, the oscillation only appears when the Nordic Sea is completely covered by sea ice in winter, and deep convection is active only near the Irminger Sea. Such conditions are provided by a substantially colder North Atlantic climate than toda

Effects of salt compensation on the climate model response in simulations of large changes of the Atlantic meridional overturning circulation

Freshwater hosing experiments with a comprehensive coupled climate model and a coupled model of intermediate complexity are performed with and without global salt compensation in order to investigate the robustness of the bipolar seesaw. In both cases, a strong reduction of the Atlantic meridional overturning circulation is induced, and a warming in the South Atlantic results. When a globally uniform salt flux is applied at the surface in order to keep the global mean salinity constant, this causes additional widespread warming in the Southern Ocean. It is shown that this warming is mainly due to heat transport anomalies that are induced by the specific parameterization in ocean models to represent eddy mixing. Surface salt fluxes tend to move outcropping isopycnals equatorward. As the density perturbation originates at the surface, changes in isopycnal slopes are generated that lead to anomalies in the bolus velocity field. The associated bolus heat flux convergence creates a warming enhancing the bipolar seesaw response, particularly in the Southern Ocean. The importance of this mechanism is illustrated in coupled model simulations in which this parameterization in the ocean model component is switched on or off. Additional experiments in which the same total amount of freshwater is delivered at rates 10 times smaller show that the effect of the global salt compensation is not important in this case, but that the eddy-mixing parameterization is still responsible for a substantial temperature response in the Southern Ocean

Methodological framework for a deeper understanding of airline profit cycles in the context of disruptive exogenous impacts

This paper combines the k-means clustering method in combination with PCA and the system dynamic modeling approach to derive a better insight into the behavior of airline profitability during the time span of 1995 until 2020. The model includes various explanatory variables that capture different aspects of airline economic and operational metrics, whose fluctuations may affect the airline profitability. By forecasting these exogenous variables, the system dynamic model is used to predict airline profitability through 2025 and answer the question of whether the US airline industry will return to its pre-COVID 19 pandemic state. The latter research question can be agreed with, as the effect of introducing a fourth dimension derived from Principal Component Analysis (PCA) to sufficiently cover the variation within the dataset during the years of COVID-19 pandemic diminishes towards the end of the forecast period. Furthermore, the key measures from PCA imply that under the assumption of continuous growth and a non-exogenous shock, future years will not cluster in past years. The six different clusters from 2019 to 2025 showed how the system stays in a certain state for a few years and then drifts further to a new state. There are only a few variables that change to transfer from one cluster to the next.Postprint (published version

The comparison of financial performance of airlines with different business model operated in long-haul market

The competition between low-cost carriers (LCC) and full-service network carriers (FSNC) has been focused exclusively on short to medium-haul markets for a long time. The launch of new aircraft generation combined with further liberalization of intercontinental air transport market presents the backbone of the recent extension of LCCs’ service into long-haul sector. Thus, the emergence of this new concept triggered the changes in the landscape of competition, since it tremendously affects the operations of incumbents, mainly FSNCs. The aim of the paper is to examine the overall profit performance of airlines with different business models (LCC vs. FSNCs) that compete in some portion of long-haul market in terms of different competitive parameters. The paper proposes the method that incorporates the major factors affecting airline profit. The method enables the construction of high level causal multidimensional plane that illustrates the behavior of profits in terms of different indicators (such as fuel costs, other operating costs excluding fuel, average stage lengths, average load factor, etc.). The conversion of these tridimensional graphs into two-dimensional one enables the researchers to easily compare the airlines’ profits under different selection of dependent variables. The results obtained in this way may have practical benefits to academics, but moreover to airline management and operations that can easily detect the major competitive advantages/disadvantages in contrast to its rival(s)

Effects of salt compensation on the climate model response in simulations of large changes of the Atlantic meridional overturning circulation

© 2007 American Meteorological Society (https://www.ametsoc.org/ams/index.cfm/publications/ethical-guidelines-and-ams-policies/ams-copyright-policy/

Indian Ocean zonal mode activity in a multicentury integration of a coupled AOGCM consistent with climate proxy data

The coupled atmosphere-ocean system over the Indian Ocean (termed Indian Ocean Zonal Mode, IOZM) and its activity over the past 200 years is analyzed in a paleoclimate simulation from a coupled atmosphere-ocean general circulation model (AOGCM). Validation shows that the AOGCM captures spatio-temporal patterns of sea surface temperature anomalies as well as the seasonal phase-locking feature of the IOZM. The period 1820–1880 exhibits a high frequency of climatically significant IOZM events, compared to a relatively low frequency in the 20th century. This shift in frequency provides a climate dynamics background for the interpretation of proxy data from East Africa, a region subjected to anomalously strong October–December precipitation during IOZM events. In the late 19th century, East African lakes had highstands (e.g., Lake Victoria) and its glaciers stable extents (e.g., Kilimanjaro), consistent with a wetter climate due to the higher frequency of IOZM events

The impact of low-cost carrier on traditional airline' fares on intercontinental routes

Text auf Serbisch, Abstract auch auf EnglischNorwegian Airlines is one of the first airlines in the world to implement a low-cost business model on long-haul flights. The low fares it has been able to offer on its intercontinental flights have seriously threatened traditional airlines, forcing them to implement various counter-strategies to reduce competitive pressure. Empirical results obtained through a regression analysis on the London-New York route indicate that the presence of low-cost carrier Norwegian has a small but statistically significant impact on the reduction of ticket prices of British Airways, which has been the dominant carrier on this route for many years. The results of the model also emphasize the importance of applying the strategy of increasing the number of seats in the passenger cabin removed by British Airways, which has proven to be an effective business tool that, through a realistically small investment in a short period of time, gives good results