Predictability of snow‐depth anomalies over Eurasia and associated circulation patterns

Interannual Variability of Snow Depth over the Tibetan Plateau and Its Associated Atmospheric Circulation Anomalies

Mitigating the impacts of droughts and floods over East Africa (EA) may largely be possible through accurate predictions of the long rains (March–May). Though the close interannual variability between the long rains, Indian and Pacific Oceans has been widely studied, Tanzania's long rain variability remains unclear. This paper examines the Tanzanian long rains dominant modes through an empirical orthogonal function (EOF) analysis, and their relationship with winter sea surface temperature (SST) for the period 1951–2018. Correlation and composite analyses were applied to explore the associated mechanisms. The first EOF (EOF1) mode is characterized by negative anomalies over Tanzania. The second EOF (EOF2) mode depicts positive (negative) anomalies over northern (southern) Tanzania. The third EOF (EOF3) mode reveals positive (negative) anomalies over eastern (western) Tanzania. EOF1 is closely related to the SST anomalies (SSTAs) in the southeastern Indian Ocean (SEIO). When the SSTAs are positive, they subsequently linked to upper (lower) level convergence (southeasterly winds) over Tanzania. Associated with this convergence entails a sinking motion, leading to a negative rainfall anomaly. The southeasterly winds indicate an early onset of the southeast monsoon, leading to normal rainfall been recorded. EOF2 is linked to the SSTAs in the central Pacific (CP). Positive SSTAs are related to reversed Walker circulation (WC) over northern Tanzania, while the upper‐level convergence was observed around southern Tanzania. This meridional dipole vertical motion pattern enhances (suppresses) rainfall anomalies. EOF3 is associated with mega El Niño–Southern Oscillation (ENSO)‐like SSTAs. The SSTAs are related to eastward shift of WC over the Indian Ocean, and zonal cell over the western Indian Ocean with rising limb is located east of Tanzania. The ascending motion enhances rainfall over eastern Tanzania. Predictions based on the SEIO, CP, and mega ENSO index may significantly support long rains prediction efforts and provide early warning.

ABSTRACTSummer precipitation in the northern China monsoon region (NCMR; 35°–55°N, 108°–135°E) shows significant intraseasonal variability. The early-summer (June) and late-summer (July–August) precipitation patterns show clear differences in their formation mechanisms and the systems that affect them. We used empirical orthogonal function (EOF) analysis to investigate the two leading modes of July–August precipitation over the NCMR and their associated atmospheric circulation anomalies using linear regression. The results show that the first (EOF1) and second (EOF2) modes correspond to a pan-NCMR precipitation variation pattern and a precipitation oscillation pattern between North China (NC) and Northeast China (NEC), respectively. These two modes account for 22.1% and 10.1% of the total variance, respectively. The associated principal components (PCs) both have significant interannual variability with a period of 2–4 years. In addition, PC1 has significant interdecadal variability with a period of 20–30 years. Further analysis suggests that EOF1 and EOF2 clearly have a different relationship with the summer monsoon circulation system. In the positive phase of PC1, the East Asian subtropical westerly jet stream (EAWJS) shows a northward trend with higher intensity than normal the blocking high at mid- to high latitudes is inactive; and the western Pacific subtropical high (WPSH) is located to the north of its normal position. The NCMR is controlled by stronger southerly winds, which cause the convergence of water vapour, favouring more precipitation in this region and vice versa. In the positive phase of PC2, the EAWJS swings to the south of Lake Baikal. Significant positive height anomalies exist from western NC to NEC. Significant negative height anomalies occur to the subtropical northwestern Pacific. This indicates that the cold vortex in Northeast China is inactive, the WPSH tends to be weaker and located to the south of its normal position, and NEC (NC) is dominated by anomalous northeasterly (southeasterly) winds. The convergence (divergence) of water vapour in NC (NEC) favours more (less) precipitation in NC (NEC) and vice versa. Therefore, EOF1 is related to the large-scale circulation anomalies over East Asia and the northwest Pacific in July and August, whereas EOF2 is more closely related to the anomalies in the regional circulation over the NCMR and the subtropical northwestern Pacific.

The influence of the Arctic Oscillation (AO) on the vertical distribution of stratospheric ozone in the Northern Hemisphere in winter is analyzed using observations and an offline chemical transport model. Positive ozone anomalies are found at low latitudes (0°–30°N) and there are three negative anomaly centers in the northern mid- and high latitudes during positive AO phases. The negative anomalies are located in the Arctic middle stratosphere (~30 hPa; 70°–90°N), Arctic upper troposphere–lower stratosphere (UTLS; 150–300 hPa, 70°–90°N), and midlatitude UTLS (70–300 hPa, 30°–60°N). Further analysis shows that anomalous dynamical transport related to AO variability primarily controls these ozone changes. During positive AO events, positive ozone anomalies between 0° and 30°N at 50–150 hPa are related to the weakened meridional transport of the Brewer–Dobson circulation (BDC) and enhanced eddy transport. The negative ozone anomalies in the Arctic middle stratosphere are also caused by the weakened BDC, while the negative ozone anomalies in the Arctic UTLS are caused by the increased tropopause height, weakened BDC vertical transport, weaker exchange between the midlatitudes and the Arctic, and enhanced ozone depletion via heterogeneous chemistry. The negative ozone anomalies in the midlatitude UTLS are mainly due to enhanced eddy transport from the midlatitudes to the latitudes equatorward of 30°N, while the transport of ozone-poor air from the Arctic to the midlatitudes makes a minor contribution. Interpreting AO-related variability of stratospheric ozone, especially in the UTLS, would be helpful for the prediction of tropospheric ozone variability caused by the AO.

We study the two primary modes of variability associated with the East Asian summer monsoon, as identified using a multivariate Empirical Orthogonal Function (EOF) analysis. The second mode is shown to be related to changes in intensity of the South Asian High at 100 hPa while, consistent with previous work, the first mode is associated with an index for the shear vorticity of the 850 hPa zonal wind over the monsoon region. We show that a linear, dry dynamical model, when driven by the diabatic heating anomalies associated with each mode, can reproduce many of the anomalous circulation features, especially for the first EOF and in the lower troposphere. The model results indicate the importance of diabatic heating anomalies over the tropical Indian Ocean in the dynamics of both modes, especially EOF-1, and illustrate the role of local diabatic feedback for intensifying the circulation anomalies; in particular, the subtropical anticyclonic anomalies that are found in the positive phase of both modes, and the circulation anomaly associated with the Meiyu/Changma/Baiu rain band. A running cross-correlation analysis shows that the second EOF is consistently linked to both the decaying and the onset phase of El Nino/Southern Oscillation (ENSO) events throughout the study period (1958-2001). We attribute the connection in the onset phase to zonal wind anomalies along the Equator in the west Pacific associated with this mode. On the other hand, a link between the first EOF and ENSO is found only in the post-1979 period. We note also the role of sea-surface temperature anomalies in the tropical Indian Ocean in the dynamics of EOF-1, and a link to the variability of the Indian summer monsoon in the case of EOF-2. Copyright © 2010 Royal Meteorological Society

The dust storm is the most important and frequent meteorological disaster over Tarim Basin, which causes huge damages on local social economics. How to predict the springtime and summertime dust storm occurrence has become a hot issue for meteorologists. This paper employed the data of dust storm frequency and 10-m wind velocity at 35 stations over Tarim Basin and the reanalysis data from the National Center for Environmental Prediction and the National Center for Atmospheric Research (NCEP/NCAR) during 1961–2007 to study the relationship between dust storm frequency (DSF) in summer over Tarim Basin and the thermal anomalies in Tibetan Plateau in May by using the statistical methods, such as Empirical Orthogonal Function (EOF), correlation and binomial moving average. The results show when negative anomalies in Tibetan Plateau and positive anomalies in its southern region are present along 30°N (the second mode of surface temperature anomalies by EOF decomposition) in May, the time coefficient (PC2) plays an important role in summer DSF variation and has a close relation with the summer DSF at both inter-annual and decadal time scales. When negative anomalies in Tibetan Plateau and positive anomalies are present in its southern region (PC2 in positive phase), there is an anomalous anticyclone in North China, which weakens the northwest wind and is not beneficial for cold air moving from high latitude to the Tarim Basin, and the circulation pattern is hard to result in dust storm weather. Furthermore, the sea level pressure (SLP) increased over Tarim Basin and the direction of SLP gradient reversed, which resulted in the 10-m wind velocity slowing down, so the DSF decreased. From above all, it can be conclude that the thermal anomalies in Tibetan Plateau in May has important effects on the summertime dust storm frequency over Tarim Basin and the PC2 can be used as a prediction factor for the summertime dust storm occurrence.

The two leading empirical orthogonal functions (EOFs) of zonal-mean zonal wind describe north–south fluctuations, and intensification and narrowing, respectively, of the midlatitude jet. Under certain circumstances, these two leading EOFs cannot be regarded as independent but are in fact manifestations of a single, coupled, underlying mode of the dynamical system describing the evolution in time of zonal wind anomalies. The true modes are revealed by the principal oscillation patterns (POPs). The leading mode and its associated eigenvalue are complex, its structure involves at least two EOFs, and it describes poleward (or equatorward) propagation of zonal-mean zonal wind anomalies. In this propagating regime, the principal component (PC) time series associated with the two leading EOFs decay nonexponentially, and the response of the system to external forcing in a given EOF does not depend solely on the PC decorrelation time nor on the projection of the forcing onto that EOF. These considerations are illustrated using results from an idealized dynamical core model. Results from Southern Hemisphere ERA-Interim data are partly consistent with the behavior of the model’s propagating regime. Among other things, these results imply that the time scale that determines the sensitivity of a model to external forcing might be different from the decorrelation time of the leading PC and involves both the rate of decay of the dynamical mode and the period associated with propagation.

Petrogenesis of Late Paleoproterozoic Liangcheng charnockites and S-type granites in the central-northern margin of the North China Craton: Implications for ridge subduction

By using the NCEP/NCAR Reanalysis dataset for 17 years (1979-1995), the structure and behaviour of quasi-stationary planetary waves (QSPWs) in the Southern hemisphere winter were studied in relation to the tropospheric zonal wind variations shown by Aoki et al. (1996). An empirical orthogonal function (EOF) analysis was made of 300 hPa height fields to detect the fluctuation of horizontal QSPW structure. The composite analysis based on the EOF analysis indicated that the QSPWs change their amplitude in the eastern hemisphere and phase in the western hemisphere between the single-jet and double-jet profiles. The wave activity flux diagnosis suggests poleward propagation from the subtropics during the period of single-jet and the equatorward propagation from polar latitudes during the double-jet period. It is shown that the horizontal EP flux divergence by total waves, especially due to high-frequency disturbances, plays an essential role in the maintenance of the difference between the two jet profiles. As regards the total (horizontal and vertical) divergences, the contribution of the QSPWs to forcing of the zonal-mean zonal wind anomalies is important in higher latitudes around 60°S.

Abstract. The ionospheric F2 peak height hmF2 is an important parameter that is much needed in ionospheric research and practical applications. In this paper, an attempt is made to develop a global model of hmF2. The hmF2 data, used to construct the global model, are converted from the monthly median hourly values of the ionospheric propagation factor M(3000)F2 observed by ionosondes/digisondes distributed globally, based on the strong anti-correlation existed between hmF2 and M(3000)F2. The empirical orthogonal function (EOF) analysis method, combined with harmonic function and regression analysis, is used to construct the model. The technique used in the global modelling involves two layers of EOF analysis of the dataset. The first layer EOF analysis is applied to the hmF2 dataset which decomposed the dataset into a series of orthogonal functions (EOF base functions) Ek and their associated EOF coefficients Pk. The base functions Ek represent the intrinsic characteristic variations of the dataset with the modified dip latitude and local time, the coefficients Pk represents the variations of the dataset with the universal time, season as well as solar cycle activity levels. The second layer EOF analysis is applied to the EOF coefficients Pk obtained in the first layer EOF analysis. The coefficients Ak, obtained in the second layer EOF analysis, are then modelled with the harmonic functions representing the seasonal (annual and semi-annual) and solar cycle variations, with their amplitudes changing with the F10.7 index, a proxy of the solar activity level. Thus, the constructed global model incorporates the geographical location, diurnal, seasonal as well as solar cycle variations of hmF2 through the combination of EOF analysis and the harmonic function expressions of the associated EOF coefficients. Comparisons between the model results and observational data were consistent, indicating that the modelling technique used is very promising when used to construct the global model of hmF2 and it has the potential of being used for the global modelling/mapping of other ionospheric parameters. Statistical analysis on model-data comparison showed that our constructed model of hmF2, based on the EOF expansion method, compares better with the observational data than the model currently used in the International Reference Ionosphere (IRI) model.

The transformation of magnetic anomalies to magnetic potential or pseudo-gravity simplifies the complexities of magnetic anomaly interpretation. We present new pseudo-gravity maps, derived from EMAG2v3 data, for the South Atlantic Ocean and adjacent continent to reveal insights into crust and lithosphere composition.The pseudo-gravity transformation of the full-field magnetic anomaly consists of three steps: (i) reduction to the pole (RTP); (ii) integration to determine magnetic potential; and (iii) scaling to determine the pseudo-gravity, assuming a constant ratio of density contrast to magnetization. This transformation produces a gravity-like anomaly that would be observed if the magnetization were replaced by a density distribution of proportional magnitude. We use magnetic data from the public domain EMAG2 v3 as the primary input. The South Atlantic region was divided into 90 tiles of 5º to account for regional variations in magnetic inclination and declination. An important assumption for the transformation is that the magnetization is induced. The pseudo-gravity mapping shows large amplitude positive anomalies consistent with the assumption of induced magnetization; negative anomalies identify areas of remnant magnetization. In the oceanic domain, alternating positive and negative anomalies reflect magnetic reversals and are not an artifact.On the South American plate, the Rio-Grande-Rise exhibits three distinct high positive pseudo-gravity anomalies, reflecting thick magmatic crust. The São-Paulo-Plateau in the Santos Basin, Florianópolis-Ridge and Torres-High also show high positive anomalies. The Campos Basin has lower-amplitude positive anomalies, suggesting localized magmatic crust. In the continents, high-amplitude positive anomalies correlate with magmatic intrusion. The high positive pseudo-gravity anomalies form an NW-SE arc from magmatic material in the Paraná Basin to the São-Paulo-Plateau, continuing through the Florianópolis-Ridge and Rio-Grande-Rise.Strong positive anomalies along the Namíbia-Ridge, Walvis-Ridge, and southwestern African margin form a "7"-shaped uniform anomaly, corresponding to magmatic crust. In contrast, the oceanic crust offshore Orange Basin shows a north-south region of negative anomalies. No significant anomalies are seen in the Tristan-Gough Guyot Province (nor are they seen on the Vitória-Trindade or Tristan-Gough Guyot Province hot-spot tracks).A comparison of the pseudo-gravity map with crustal thickness from gravity inversion shows that many large, high-amplitude positive pseudo-gravity anomalies in the oceanic domain correlate strongly with anomalously thick crust (>12.5 km thickness) on the Rio-Grande-Rise, São-Paulo-Plateau, Florianópolis-Ridge, Namíbia-Ridge and Walvis-Ridge. Plate reconstruction of pseudo-gravity anomalies and crustal thickness suggest that the Namíbia-Ridge and western Florianópolis-Ridge, both with thick magmatic crust, have a common origin at approximately 110 Ma but were later separated by the Florianópolis-Fracture-Zone. The spatial relationship of observed high positive pseudo-gravity anomalies on magmatically intruded crust in the South American and African continents, the hybrid or magmatic crust on their rifted margins and thickened magmatic crust within the South Atlantic shows the major role of mantle inheritance in their origin.

By using the second version of the Community Atmosphere Model (CAM2) of NCAR, the general circulations of the Earth's atmosphere were simulated under different rotation rates conditions. The results imply that the intensity of three-cell circulation turn strong when the rotation rate turn slow. Furthermore, under slow rotation rate, for annual mean temperature field, there exist the negative anomalies in the Northern Hemisphere and positive anomalies in the Southern Hemisphere. The region of negative anomaly and that of positive anomaly are divided by 15°S. The annual mean zonal wind field has positive anomaly and negative anomaly when the roattion rate is changed. The positive anomalies and negative anomalies are cross. Compared with summer and autumn, in spring, the changes of geopotential height field, temperature field, meridional wind field in the stratosphere and vertical velocity field are opposite under different rotation rates. Compared with annual mean result, the situation of these three fields is reverse. The westerly in mid-latitude are all strengthened in four seasons under slow rotation rate. The change trends of the zonal wind in two Hemisphere are opposite in spring and autumn. The changes of physical quantities have significant seasonal difference. The change in autumn is the biggest. For monsoon, there are three regions of the linear response - African, Middle East and temperate zone and Frigid Zone.

The El Niño–Southern Oscillation (ENSO) and the quasi-biennial oscillation (QBO) are two major interannual variations observed in the tropics, yet the joint modulation of the ENSO and QBO on the ozone valley over the Tibetan Plateau (TP) in summer has not been performed. This study investigates the combined effects of the ENSO and the QBO on the interannual variations of the ozone valley over the TP using the ERA5 reanalysis data from 1979 to 2021. The results show that the ENSO leads the zonal deviation of the total column ozone (TCO*) over the TP by about 6 months. This means the TCO* in the summer of the following year is affected by the ENSO in the current year. This is consistent with the theory of recharge oscillation. In terms of dynamic conditions, the anomalous circulation resulting from the combined effect of El Niño and the easterly phase of the QBO (EQBO) lead to strengthened and upward anomalies of the South Asian high (SAH) over the TP, followed by reduced ozone valley with more negative anomalies over the TP in summer. As to thermodynamic conditions, affected by both El Niño and the EQBO, the atmospheric stability shows positive anomalies from the lower troposphere to the upper troposphere, and the positive anomaly areas are larger than those in other conditions. These findings indicate an unstable atmosphere, where convection is more likely to cause ozone exchange. The turbulent mixing of ozone at low levels and high levels leads to the ozone valley over the TP, with more negative anomalies in the upper troposphere and lower stratosphere (UTLS).

Coastal stations are critical for interpretation of continental‐scale CO2 exchanges although the impacts of land and sea breezes, local topography, katabatic winds, and CO2 transport from nearby terrestrial ecosystems are not well characterized. We applied a modeling framework that couples meteorological (MM5), land‐surface (LSM1), and tracer models to investigate the impact of these factors on coastal CO2 measurements. Model predictions compared well with measurements over 4 months at our case study site (Trinidad Head, California). We predicted that during midday and under strong onshore wind conditions, positive and negative CO2 anomalies from the assumed “background” marine layer air were sampled at the station. These anomalies resulted from two classes of mechanisms that couple transport and recent terrestrial ecosystem exchanges. First, and most important, are local and large‐scale recirculation of nighttime positive CO2 anomalies resulting from katabatic flows off the coastal mountain range. Second, negative anomalies generated by daytime net ecosystem uptake can be transported offshore in the residual layer and then entrained in the marine boundary layer. We predicted monthly averaged CO2 anomalies associated with terrestrial exchanges of 0.53, 0.34, 3.1, and 0.05 ppm during March, June, September, and December of 2002. Positive anomalies from nighttime ecosystem respiration were more likely to be sampled than are negative anomalies associated with daytime net ecosystem uptake. Current atmospheric models used in continental‐scale inverse studies do not resolve these two classes of mechanisms and therefore may infer incorrect CO2 exchange rates.

Through observational analysis and atmospheric simulation experiments, the relationship between sea ice in the region of South Pole and August precipitation in China was determined. Results indicate that the leading mode of August precipitation in China is significantly correlated with July sea ice concentration (SIC) in South Pole, specifically in eastern Indian Ocean (EIO) region. Typically, the SIC growth is followed by positive rainfall anomalies in the middle and lower reaches of Yangtze River Basin (YRB) and Northeast China (NEC), while South China (SC) is under the control of negative rainfall anomalies. Precisely, owing to the temporal persistence of sea ice in the South Polar region from May to August, sea ice anomalies exert a strong influence on August atmospheric stability in EIO of Southern Hemisphere via regulating turbulent heat flux and air temperature anomalies. As SIC increases, the atmospheric circulation in horizontal exhibits the characteristics of the Antarctic Oscillation (AAO) positive phase, affecting the zonal wind anomalies. Subsequently, the anomalous circulation with a barotropic structure propagates to Australia and the East Asian via the strengthened vertical meridional cells and zonal winds. Moreover, numerical simulations confirm that due to the growth of South Polar sea ice in EIO, abnormal cyclone and anticyclone appear over North China and SC respectively, together with the moisture converging anomalies in the middle and lower reaches of YRB, and diverging anomalies in SC. Accordingly, these atmospheric circulation anomalies triggered by Antarctic sea ice conducive to a wet (dry) August in northern (southern) China.