Simulation of the ENSO influence on the extra-tropical middle atmosphere

Abstract The impact of the El Niño Southern Oscillation (ENSO) on the Northern Hemisphere mid-winter zonal wind, temperature, and stationary planetary waves (SPWs) is evaluated using the Middle and Upper Atmosphere Model and Modern-Era Retrospective Analysis for Research and Applications (MERRA). The composites determined using simulated ensembles and MERRA winters with different ENSO phases show that the mean zonal wind in the stratosphere at higher-middle latitudes is weaker and polar region is warmer, and the activity of SPW1 is higher during El Niño events. The simulated and observed SPW2 amplitude behaves in the opposite way, and it is stronger in the stratosphere during La Niña. The observed changes of SPW1 and SPW2 amplitudes under La Niña and El Niño events should affect an efficiency of the stratosphere–troposphere coupling in different longitudinal sectors through the changes in horizontal distributions of the downward wave activity flux

Manifestations of Different El Niño Types in the Dynamics of the Extratropical Stratosphere

The behavior of planetary waves and their influence on the global circulation of the Northern Hemisphere during different El Niño types is studied. Three sets of five boreal winters were chosen for each El Niño type: Modoki I and II and canonical El Niño. Based on data of the Japanese 55-year Reanalysis and the Modern-Era Retrospective Analysis for Research and Applications, the spatio-temporal structure of planetary waves and the residual mean circulation were analyzed. The results show that the canonical El Niño type is characterized by the weakest wave activity in March. It is also demonstrated that warming of the polar stratosphere, accompanied by maximizing wave activity and weakening of the zonal wind, may lead to earlier stratospheric polar vortex collapse and the early spring transition under Modoki I conditions. This study is the next step in understanding of the so-called long-range teleconnections, consisting of the propagation of a signal from the tropical El Niño Southern Oscillation source into the polar stratosphere

Manifestations of Different El Niño Types in the Dynamics of the Extratropical Stratosphere

The behavior of planetary waves and their influence on the global circulation of the Northern Hemisphere during different El Niño types is studied. Three sets of five boreal winters were chosen for each El Niño type: Modoki I and II and canonical El Niño. Based on data of the Japanese 55-year Reanalysis and the Modern-Era Retrospective Analysis for Research and Applications, the spatio-temporal structure of planetary waves and the residual mean circulation were analyzed. The results show that the canonical El Niño type is characterized by the weakest wave activity in March. It is also demonstrated that warming of the polar stratosphere, accompanied by maximizing wave activity and weakening of the zonal wind, may lead to earlier stratospheric polar vortex collapse and the early spring transition under Modoki I conditions. This study is the next step in understanding of the so-called long-range teleconnections, consisting of the propagation of a signal from the tropical El Niño Southern Oscillation source into the polar stratosphere

High northern latitude surface air temperature: comparison of existing data and creation of a new gridded data set 1900-2000

Detection, attribution and understanding of temperature changes in the high northern latitudes depend on constraining uncertainties and resolving apparent discrepancies in observational data sets. We quantitatively compare four of the most widely used data sets of surface air temperature (SAT), and present a newly produced SAT data set, called NansenSAT. The existing data sets are highly correlated (r ∼ 0.8–0.9), except for some ocean areas. The evolution of SAT anomalies indicates differences reaching 3 ◦ C during the 1920s–1930s warming period for the polar region (60–90◦ N). Substantial errors in trends also result from spatial sampling limitations, especially during the early–20th-century. Maximum differences between the data sets reaching 0.64 ◦ C/100 yr are found in 1900–1999 linear trends in July and October for 60–90◦ N. We produced a new SAT data set for the region north of 40◦ N for the period 1900–2000, using all available data and Objective Analysis methods. The new data set has been compared with existing SAT data. For the polar region, the magnitude of temperature-trend errors caused by sparse data coverage is about 0.5 ◦ C/100 yr. The advantage of the new data set is its enhanced spatial coverage in high latitudes. The NansenSAT data set is available for the research community