northern winter
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MAUSAM ◽  
2021 ◽  
Vol 43 (4) ◽  
pp. 385-394
Author(s):  
P.N. PATHAK ◽  
N. GAUTAM

The main purpose of the present work is to establish the reliability of the SAMIR-derived water vapour (WV) data over the Arabian Sea and the Bay of Bengal for the entire 18-month from January 1982 to June 1983 period of the in-orbit operation of the SAMIR system. The average latitudinal distributions of WV over the Arabian Sea and Bay of Bengal for different months, derived from the SAMJR data were found to be broadly consistent with the climatological data on WV from the coastal and island radiosonde stations.   A significant latitudinal gradient in WV has been found during the northern winter months (Dec-Feb) with the highest value of 4-5 gm/cm2 near the equator and thc lowest value of about 2 gm/cm2 at about 20oN over the Indian seas. This gradient gradually decreases during the subsequent months and almost vanishes during the southwest monsoon months (Jun-Sep) when the WV has nearly uniform value of 4-5 gm/cm2 in the entire latitude range from the equator to 20oN over the Indian seas. Finally, it has been found that WV values over the Bay of Bengal are generally higher than those over the Arabian Sea at co-latitudinal positions. The implications of this result are discussed in the light of other considerations.


Agronomy ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 1845
Author(s):  
Yu Zhang ◽  
Xiaolei Qiu ◽  
Tingwei Yin ◽  
Zhiyi Liao ◽  
Bing Liu ◽  
...  

The impact of global warming on crop growth periods and yields has been evaluated by using crop models, which need to provide various kinds of input datasets and estimate numerous parameters before simulation. Direct studies on the changes of climatic factors on the observed crop growth and yield could provide a more simple and intuitive way for assessing the impact of climate change on crop production. In this study, four cultivars which were planted over more than 15 years in eight test stations in the Northern Winter Wheat Region of China were selected to investigate the relationships between growth periods, grain yields, yield components and temperatures. It was found that average temperatures and heat degree-days (HDD) during the winter wheat growing seasons tended to increase over time series at most study sites. The length of growth period and growing degree days (GDD) were not fixed for a given cultivar among different years and locations, and the variation on the periods from sowing to jointing was relatively greater than in the other periods. The increasing temperature mainly shortened the periods from sowing to jointing and jointing to anthesis, which led to the decrease in entire growth periods. Positive relationships between spike number, grain number per spike, grain yields and average temperatures were identified in the Northern Winter Wheat Region of China. The grain yield in the study area increased by 406.3 kg ha−1 for each 1 °C increase in average temperature. Further, although the positive relationship between grain yield and HDD was found in our study, the heat stress did not lead to the wheat yield decline in the study region. Temperature is a major determinant of wheat growth and development, the average temperature and the frequency of heat stresses are projected to increase in the future, so understanding the effect of temperature on wheat production and adopting appropriate adaptation are required for the implementation of food security policies.


2021 ◽  
pp. 1-53
Author(s):  
Hua Lu ◽  
Lesley J. Gray ◽  
Patrick Martineau ◽  
John C. King ◽  
Thomas J. Bracegirdle

AbstractA new regime index is constructed to capture the seasonal development of the stratospheric polar vortex in the northern winter, based on the standard deviation of Ertel’s potential vorticity in the upper stratosphere in November-December. The narrow-jet flow regime is characterized by a polar vortex that is more confined to high latitudes in the early winter upper stratosphere. This upper-level vortex configuration is more susceptible to the disturbances of upward propagating planetary-scale Rossby waves; the stratospheric polar vortex thus weakens earlier and is vertically shallower. The wide-jet flow regime is characterized by a broader-than-average polar vortex that extends further into the subtropics in the early-winter upper stratosphere. The polar night jet then gradually strengthens, moves poleward and penetrates deep into the lowermost stratosphere, with a sharply-defined polar vortex edge accompanied due to more frequent Rossby wave breaking.Composite differences analyses show that the wide and narrow jet regimes, defined in the uppermost stratosphere in November-December, lead to different circulation anomalies of the lower-stratosphere and the troposphere in January-February, offering the potential for improved predictability of sub-seasonal to seasonal forecasts up to two months ahead. The lower tropospheric responses in January-February are zonally asymmetric. The narrow-jet regime projects most strongly over the North Atlantic, with an equatorward-shifted, and/or broader mid-latitude westerly jet. The wide-jet-regime response is characterized by a weakened mid-latitude westerly jet over the North Pacific. The two flow regimes also differ in their impacts on the storm track over Western Europe and the east coast of America, which may have implications for extreme weather events in those regions.


2021 ◽  
Author(s):  
Ho Nam Cheung ◽  
Noel Keenlyside ◽  
Torben Koenigk ◽  
Shuting Yang ◽  
Tian Tian ◽  
...  

Abstract We investigate the uncertainty (i.e., inter-model spread) in future projections of the northern winter climate, based on the forced response in the CMIP5 RCP8.5 scenario. The uncertainty in the forced response of sea level pressure (SLP) is large in the North Pacific, the North Atlantic, and the Arctic. A major part of these uncertainties (31%) is marked by a pattern with a center in the northeastern Pacific and a dipole over the northeastern Atlantic that we label as the Pacific–Atlantic SLP uncertainty pattern (PAΔSLP). To better understand the nature of PAΔSLP, the associated sea surface temperature (SST) and Arctic sea ice cover (SIC) perturbation patterns are prescribed in experiments with two atmospheric models (AGCMs): CAM4 and IFS.The AGCM experiments indicate more robust SLP response over the North Pacific driven by the SST perturbation, which is associated with the tropical-midlatitude interaction and the Rossby wavetrain. The North Atlantic SLP response is better explained by the joint effect of SST and SIC perturbations, which is partly related to the Rossby wavetrain from the Pacific and the air–sea interactions over the North Atlantic. However, these responses shift westward relative to PAΔSLP, where in CAM4 it is related to the low-frequency transient eddy forcing. The magnitude of these responses in the two AGCMs is largely different. Thus, constraining only the SST and SIC projections might not alone help constrain future climate projections. We should investigate the role of other factors in these uncertainties, such as the atmosphere–SST–SIC coupled dynamics.


Author(s):  
Benjamin M. Winger ◽  
Teresa M. Pegan

AbstractSeasonal migration is a widespread adaptation in environments with predictable periods of resource abundance and scarcity. Migration is frequently associated with high mortality, suggesting that migratory species live on the “fast” end of the slow-fast continuum of life history. However, few interspecific comparative studies have tested this assumption and prior assessments have been complicated by environmental variation among breeding locations. We evaluate how migration distance influences the tradeoff between reproduction and survival in 45 species of mostly passerine birds that breed sympatrically in North American boreal forests but migrate to a diversity of environments and latitudes for the northern winter. We find, after accounting for mass and phylogeny, that longer distance migrations to increasingly amenable winter environments are correlated with reduced annual reproductive output, but also result in increased adult survival compared to shorter-distance migrations. Non-migratory boreal species have life history parameters more similar to long-distance migrants than to shorter-distance migrants. These results suggest that long-distance migration and other highly specialized strategies for survival in seasonal environments impose selection pressures that both confer and demand high adult survival rates. That is, owing to the reproductive cost of long-distance migration, this strategy can only persist if balanced by high adult survival. Our results reveal migratory distance as a fundamental life history parameter that predicts, and is inextricable from, the balance of survival and reproduction. Our study further provides evolutionary context for understanding the annual cycle demography of migratory species and the strategies long-distance migrants use to maximize survival on their journeys.


2020 ◽  
Vol 33 (11) ◽  
pp. 4787-4813 ◽  
Author(s):  
Jian Rao ◽  
Chaim I. Garfinkel ◽  
Ian P. White

AbstractUsing 16 CMIP5/6 models with a spontaneously generated quasi-biennial oscillation (QBO)-like phenomenon, this study investigates the impact of the QBO on the northern winter stratosphere. Eight of the models simulate a QBO with a period similar to that observed (25–31 months), with other models simulating a QBO period of 20–40 months. Regardless of biases in QBO periodicity, the Holton–Tan relationship can be well simulated in CMIP5/6 models with more planetary wave convergence in the polar stratosphere in easterly QBO winters. This wave polar convergence occurs not only due to the Holton–Tan mechanism, but also in the midlatitude upper stratosphere where an Elissen–Palm (E-P) flux divergence dipole (with poleward E-P flux) is simulated in most models. The wave response in the upper stratosphere appears related to changes in the background circulation through a directly excited meridional–vertical circulation cell above the maximum tropical QBO easterly center. The midlatitude upwelling in this anticlockwise cell is split into two branches, and the north branch descends in the Arctic region and warms the stratospheric polar vortex. Most models underestimate the Arctic stratospheric warming in early winter during easterly QBO. Further analysis suggests that this bias is not due to an overly weak response to a given QBO phase, as the models simulate a realistic response if one focuses on similar QBO phases. Rather, the model bias is due to the too-low frequency of strong QBO winds in the lower stratosphere in early winter simulated by the models.


2020 ◽  
Vol 46 (8) ◽  
pp. 1166-1173
Author(s):  
Xiao-Qing ZHANG ◽  
Zi-Guang YANG ◽  
Xiao-Ni YANG ◽  
Li-Lei GUO ◽  
Nai-Yin XU ◽  
...  

2020 ◽  
Author(s):  
Rongcai Ren ◽  
Xin Xia ◽  
Jian Rao

<p>This study uses the stratosphere-resolved Whole Atmosphere Community Climate Model to demonstrate the “independent” and “dependent” topographic forcing from the topography of East Asia (EA) and North American (NA), and their “joint” forcing in the northern winter stratosphere. The mutual interference between the EA and NA forcing is also demonstrated. Specifically, without EA, an independent NA can also, like EA, induce a severe polar warming and weakening of the stratospheric polar vortex. While EA favors a displacement of the polar vortex toward Eurasia, NA favors a displacement toward the North America–Atlantic region. However, the independent-EA-forced weakening effect on the polar vortex can be largely decreased and changes to a location displacement when NA exists, and the interference the other way around is even more critical, being able to completely offset the independent-NA-forced effect, because EA can substantively obstruct NA’s effect on the tropospheric wave pattern over the Eurasia–Pacific region. The much stronger/weaker interference of EA/NA is associated with its stronger/weaker downstream weakening effect on the zonal flow that impinges on NA/EA. The mutual interference always tends to further destruct the upward wave fluxes over the eastern North Pacific and enhance the downward wave fluxes over NA. The overall changes in upward wave fluxes, as well as that in the Rossby stationary wavenumber responsible for the stratospheric changes, are related to changes in the zonal-mean flow pattern. The joint effects of EA and NA, rather than being a linear superimposition of their independent effects, are largely dominated by the effects of EA.</p>


2020 ◽  
Author(s):  
Jone Peter Reistad ◽  
Anders Ohma ◽  
Karl Magnus Laundal ◽  
Therese Moretto ◽  
Steve Milan ◽  
...  

<p>Presently, all empirical coupling functions quantifying the solar wind - magnetosphere energy- or magnetic flux conversion, assume that the coupling is independent of the sign of the dawn-dusk component (By) of the Interplanetary Magnetic Field (IMF). In this paper we present observations strongly suggesting an explicit IMF By effect on the solar wind - magnetosphere coupling. When the Earth's dipole is tilted in the direction corresponding to northern winter, positive IMF By is found to on average lead to a larger polar cap than when IMF By is negative during otherwise similar conditions. This explicit IMF By effect is found to reverse when the Earth's dipole is inclined in the opposite direction (northern summer), and is consistently observed from both hemispheres using the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) to infer the size of the region 1/2 current system. Two interpretations are presented: 1) The dayside reconnection rate is affected by the combination of dipole tilt and IMF By sign in a manner explaining the observations 2) The combination of dipole tilt and IMF By sign affect the global conditions for maintaining a given nightside reconnection rate. The observations as well as idealized magnetohydrodynamic (MHD) model runs are analyzed and discussed in light of the two different interpretations in order to enhance our understanding of this explicit IMF By effect.</p>


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