Influence Of Arctic Oscillation Research Articles

Influence of Arctic Oscillation on Frequency of Wintertime Fog Days in Eastern China

The influence of Arctic Oscillation (AO) on the frequency of wintertime fog days in eastern China is studied based on the winter AO index, the wintertime fog-day data of national stations in China, and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis data from 1954 to 2007. The results show that heavy fog and light fog are more likely to occur during winter in eastern China with the strong interannual variability. During the winter with the positive-phase AO, there are more days of heavy fog in North China but less in South China, while light fog days become more in the whole of eastern China. It is mainly because that when AO is in the positive phase, the pressure in the polar region decreases at 500 hPa; the pressure in East Asia increases anomalously; the East Asian trough decreases; and the low-level westerly jet moves northward, preventing the northwesterly cold air from moving southward. Therefore, the whole eastern China gets warmer and wetter air, and there are more light fog days with the enhanced water vapor. However, the atmosphere merely becomes more towards unstable in South China, where the precipitation increases but the heavy fog days decreases. Nevertheless, heavy fog days increase with the water vapor in North China because of moving towards a stable atmosphere, which is formed by the anomalous downdrafts north of the precipitation center in South China. When AO is in the negative phase, the situation is basically opposite to that in the positive phase, but the variations of the corresponding fog days and circulations are weaker than those in the AO-positive-phase winter, which may be related to the nonlinear effect of AO on climate.

北极涛动对我国冬季气温的影响

北极涛动对我国冬季气温的影响

Possible Influence of Arctic Oscillation on Winter Visibility over Eastern China

NCEP/NCAR reanalysis data, the Arctic Oscillation (AO) index and the atmospheric visibility (Vis) data at 134 sites in eastern China (ECN) are used to investigate the possible influence of AO on the wintertime weather and Vis over ECN. A higher relative humidity (RH, compared with the normal year) is identified over ECN in the winters with a positive phase of AO, and the wind anomaly is generally inshore in the coast areas of China. All these processes are consistent with Vis degradation over ECN. On the contrary, in the winters with a negative phase of AO, a lower RH can be identified over ECN, and the wind anomaly is generally offshore, which is favorable for Vis improvement.

Possible influence of Arctic oscillation on precipitation along the East Asian rain belt during boreal spring

In this study, the possible influence of the springtime Arctic oscillation (AO) on precipitation along the East Asian rain belt has been studied for the period of 1979 to 2014. To capture the features of the large-scale variability of the atmospheric circulation and precipitation, singular value decomposition (SVD) analysis was performed. The domain for precipitation is from 21.25 to 33.75° N and 111.25 to 133.25° E, and the 1000 hPa heights are from 20° N northward. Prior to analysis, the El Nino-Southern Oscillation (ENSO) signals were linearly fitted and subtracted from the variables of interest. The first paired modes explain 51.1 % of the total squared covariance. The spatial feature of the pressure mode is almost identical to that of the positive AO pattern, while the precipitation mode displays an overall less-than-normal anomaly along the rain belt. The AO indices are highly correlated with the time coefficients of the pressure mode at a value of 0.91, and for the time coefficients of the precipitation mode, the correlation is −0.44, both of which are significant at the 99 % level. The regional atmospheric circulation anomalies in association with the negative phase AO mode display consistent changes, including the anomalous southerly winds and vapor flux convergence in the lower troposphere over East Asia, the stronger East Asian westerly jet stream, and the enhanced ascending air motion between 20 and 30° N. There are two possible mechanisms linking the AO and East Asian circulation and precipitation, i.e., the wave-trains along the westerly jet stream from North Africa to the Middle East and East Asia and the dipole of an anti-cyclone and a cyclone over the North Pacific.

The possible influence of Arctic Oscillation on South China Sea climate during boreal spring

In this study, the possible influences of the springtime Arctic Oscillation (AO) on climate over South China Sea (SCS) has been studied, by employing monthly precipitation data (GPCP) and atmospheric circulation reanalysis data from NCEP-NCAR during the period of 1979-2013. Prior to analysis, the El Nino-Southern Oscillation (ENSO) signals have been linearly fitted and subtracted from the time series under consideration. To capture the major feature of the regional climate variability, multi-variable empirical orthogonal function (MV-EOF) analysis was performed, by taking into account sea surface temperature (SST), precipitation, and horizontal and vertical winds at 850 hPa over the domain of 3.75°S-23.75°N and 106.25°E-123.75°E. The first mode explains 27.8% of the total variance. The corresponding temporal variations of the first mode co-changes tightly with the spring AO. Their correlation coefficient is -0.4, being significant at the 0.05 level. Their out-of-phase relationship is even more dominant on the interannual time scales. During positive (negative) AO years, a cyclonic (anticyclonic) anomalous circulation is observed over the tropical Western Pacific in the mid- and lower troposphere. There are more (less) precipitation in the central SCS, corresponding to the circulation anomalies. There are two possible mechanisms linking AO and SCS climate. The first mechanism is the wave train along the westerly jet stream extending from northern Africa through mid-Asia to northern India. Along this route, there are two anomalous circulation centers in the upstream direction, one being located in the Bay of Bengal, and the other located in the Arabian Sea. The second mechanism seems to be related to the dipole-structure circulation anomalies over the North Pacific, which characterized by a dipole of anticyclone and cyclone located to the north and south of the northern Pacific storm tracks, respectively. Their phase and corresponding circulation center locations are crucial with regard to the AO-SCS links. In cases of a strong positive phase of southern Asian waves and negative phase of northern Pacific dipole, there is an enhanced anticyclone circulation over the SCS and reduced precipitation. In addition to the influences on the SCS climate from the atmosphere, positive feedback from the tropical western Pacific Ocean strengthens the anomalous north winds of SCS. Local SST of SCS mainly responds to (rather than affects) the atmospheric circulation.

Evaluation of glacier changes in high‐mountain Asia based on 10 year GRACE RL05 models

AbstractIn this paper, 10 years of time‐variable gravity data from the Gravity Recovery and Climate Experiment Release 05 have been used to evaluate the glacier melting rate in high‐mountain Asia (HMA) using a new computing scheme, i.e., the Space Domain Inverse method. We find that in HMA area, there are three different kinds of signal sources that should be treated together. The two generally accepted sources, glacier melting and India underground water depletion, are estimated to change at the rate of −35.0 ± 5.8 Gt/yr (0.09 mm/yr sea level rising) and −30.6 ± 5.0 Gt/yr, respectively. The third source is the remarkable positive signal (+30 Gt/yr) in the inner Tibetan Plateau, which is challenging to explain. Further, we have found that there is a 5 year undulation in Pamir and Karakoram, which can explain the controversies of the previous studies on the glacier melting rate here. This 5 year signal can be explained by the influence of Arctic Oscillation and El Niño–Southern Oscillation.

Influence of Arctic Oscillation on dust activity over northeast Asia

Abstract The northeast Asian dust process during the spring seasons in the years 1982–2006 was simulated by the Integrated Wind Erosion Modeling System (IWEMS). The influence of Arctic Oscillation (AO) on dust activities was investigated by analyzing surface observations and model simulations. There is a significant relationship between AO and dust activity; a positive AO phase is associated with decreased (increased) dust storm frequency in Mongolia (Taklimakan Desert) and enhanced anticyclonic (southeastward) dust transport over northwestern China (North China). The AO-dust relation is mainly due to changes in the westerly jet and geopotential height in the middle troposphere; a positive AO phase induces a northward shift of the polar jet, an intensified westerly jet over northern Tibetan Plateau, and a positive geopotential height anomaly over Mongolia. The northern shift of the polar jet reduces the frequency of intense cyclones in Mongolia, thereby causing a decrease in the dust storm frequency. The intensified westerly jet stream over the northern Tibetan Plateau increases the dust storm frequency in the Taklimakan Desert. The positive geopotential height anomaly over Mongolia initiates an anticyclonic dust transport anomaly in the middle troposphere over northwestern China. It also induces a southeastward dust transport anomaly over North China. The reverse situations are true for a negative AO phase.

Influence of Arctic Oscillation towards the Northern Hemisphere Surface Temperature Variability under the Global Warming Scenario

Future projection of the Arctic Oscillation (AO) signature and its significance towards the northern hemispheric surface temperature trend have been examined using 20 state-of-the-art Atmosphere-Ocean General Circulation Model (AOGCM) outputs forced under the IPCC SRES-A1B and 20C3M emission scenario. Models are mostly successful in simulating the observed AO structure and the corresponding surface temperature variability. It is found that while AO exhibits a large positive trend, especially during the autumn season with a relatively smaller trend during the winter and spring seasons. In all seasons the interannual variance in AO remains the same for both scenarios. These features in the timeseries leads to two distinct patterns of temperature variability. One is the "polar amplification" pattern due to the long-term anthropogenic forcing, which is much larger in its amplitude. Another is related to the natural variability of the AO, which is confined over the land surface and is marked by a dipole pattern of temperature between the Eurasian continent and Greenland. It is argued that the gradual trend in the AO is not a result of enhanced natural variability of the AO dynamics itself, but rather a result of the large anthropogenic forced linear trend projected onto the mean climatological state of the Arctic region. Distinguishing these two patterns of warming is crucial for detecting the signal of future global warming trend over the Eurasian continent and other regions.

Arctic Oscillation influence on daily temperature variance in winter over China

The relationship between the Arctic Oscillation (AO) and daily temperature variance of 150 Chinese stations are investigated in the present study for wintertime (1November through 31 March) in the period of 1954–2001. Results show that the temperature variance significantly decreases during the high AO years, and increases in low AO cases. A key factor connecting them is the Siberian High, particularly the high-frequency fluctuations of the High. Within the seasonal time scale, the frequency of low-temperature extremes (daily temperature anomaly below −2σ, σ is the standard deviation of daily temperature for a given winter and a given station) displays an odd relation to the variance: a larger (smaller) variance is found to be associated with smaller (greater) frequency of low-temperature events. That is due to the non-normal distribution of the temperatures, and also influenced by the phases of AO. During the last 50 years or so, AO experiences a significant increasing trend, meanwhile the variance of daily sea level pressure (SLP) in the central region of Siberian High has decreased at a rate of −10.7%/10 a. These result in a significant weakening of the daily temperature variance in China with a trend of −4.1%/10 a, and a significant increase in the intra-seasonal low-temperature extremes at a rate of 0.16d/10 a.

Influence of Arctic Oscillation on winter climate over China

In this study the relationship between the Arctic Oscillation (AO) and climate in China in boreal winter are investigated. Correlation analysis for the last 41 years shows that the winter temperature and precipitation in China change in phase with AO. High positive correlation (>0.4) between temperature and AO appears in the northern China. High correlation coefficients between precipitation and AO cover the southern China (close to the South China Sea) and the central China (between 30°-40°N and east of 100°E), with the values varying between +0.3 and +0.4. It is found that during the past several decades the precipitation was strongly affected by AO, but for the temperature the Siberian High plays a more important role. At the interdecadal time scale the AO has significant influence on both temperature and precipitation. Multivariate regression analysis demonstrates that AO and the Siberian High related variance in temperature and precipitation is 35% and 11% respectively. For precipitation, however the portion is rather low, implying that some other factors may be responsible for the changes in precipitation, in addition to AO and the Siberian High.