Meteorological factors associated with July 2005 floods in river Jhelum

The meteorological conditions leading to the July, 2005 floods in river Jhelum in the state of Jammu & Kashmir have been analyzed in the present study. The floods coincided with a spell of heavy rains over the state during second week of July 2005 caused by the interaction of a westward moving monsoon disturbance over the plains of northwest India and an eastward moving trough in middle troposphere over north Pakistan. Further analysis of precipitation over the state during the preceding winter season shows that there was record snowfall at many stations over the state. The estimate from KALPANA-1 satellite also revealed the highest snow cover area over the region since 1998. The higher volume of snowmelt because of the increased snow cover area seems to have significantly contributed towards the floods.

The Synergistic Effect of The Preceding Winter Northern Hemisphere Annular Mode and Spring Tropical North Atlantic SST On Spring Extreme Cold Events in The Mid-high Latitudes of East Asia

In this paper, the synergistic effect of the preceding winter positive Northern Hemisphere annular mode (pNAM) and spring negative tropical North Atlantic (nTNA) sea surface temperature anomaly (SSTA) on spring extreme cold events in the mid-high latitudes of East Asia (MHEA) is investigated. The results show that the co-occurrence of the two factors is unfavorable for extreme cold events during spring in the MHEA via the snow cover and atmospheric bridges. Over the Atlantic, the spring nTNA SSTA can lead to an atmospheric response that is similar to the North Atlantic Oscillation (NAO), which enhances the persistence of the pNAM and in turn amplifies the negative spring Eurasian snow cover extent (EASCE) anomaly caused by the preceding winter pNAM. Meanwhile, the spring EASCE is closely related to the spring MHEA anomalous anticyclone. In addition to storing its signal in the spring EASCE, the spring nTNA SSTA can also lead to the spring MHEA anomalous anticyclone via the eastward Rossby wave train. The evidence shows that the Rossby wave energy can propagate eastward to the MHEA as a result of the enhanced negative spring EASCE anomaly and Rossby wave induced by the spring nTNA SSTA, and the two factors have an obvious synergistic effect on the spring MHEA anomalous anticyclone. This anomalous MHEA anticyclone becomes a barrier that can hinder the intrusion of cold air from the polar region and can increase the thickness of the atmospheric layer. The anomalous sinking motion of the spring MHEA anomalous anticyclone can also lead to an increase in net radiation received at the surface and increase the air temperature through the vertical motion of air. The southerly wind over the west side of the spring MHEA anomalous anticyclone leads to horizontal warm advection. All of the above processes favor an increase in air temperature and dampen extreme cold events, implying the synergistic effect of the preceding winter pNAM and spring nTNA SSTA on spring extreme cold events in the MHEA.

A new classification of the Arctic spring transition in the middle atmosphere

<p>In the middle atmosphere, spanning the stratosphere and mesosphere, spring transition is the time period where the zonal circulation reverses from winter westerly to summer easterly which has a strong impact on the vertical wave propagation influencing the tropospheric and ionospheric variability. The spring transition can be rapid in form of a final sudden stratospheric warming (SSW, mainly dynamically driven) or slow (mainly radiatively driven) but also intermediate stages can occur. In most studies spring transitions are classified either by their timing of occurrence or by their vertical structure. However, all these studies focus exclusively on the stratosphere and can give only tendencies under which pre-winter conditions an early or late spring transition takes place and how it takes place. Here we classify the spring transitions regarding their vertical-temporal development beginning in January and spanning the whole middle atmosphere in the core region of the polar vortex. This leads to five classes where the timing of the SSW in the preceding winter and a downward propagating Northern Annular Mode (NAM) plays a crucial role. The results show distinctive differences between the five classes in the months before the spring transition especially in the mesosphere allowing a certain prediction for some of the five spring transition classes which would not be possible considering the stratosphere only.</p>

Dependence of Beaufort Sea Low Ice Condition in the Summer of 1998 on Ice Export in the Prior Winter

Four events of distinctly low summer ice coverage in the Beaufort Sea, in 1998, 2008, 2012, and 2016, have been identified using satellite-observed concentration between 1979 and 2017. Previous studies have revealed that these four minima were impacted by preconditioning of the ice cover, and specifically the 1998 event was preconditioned toward thinner ice by anomalous southeasterly winds during winter. This study further investigates the 1998 event through analyzing the solution of a coupled ocean and sea ice model. Compared with the mean condition during 1995–2015, the net ice loss in the melt season (May–September) of 1998 was not particularly high. In the preceding fall (October–December 1997), the ice conditions and processes contributing to ice changes were neither significantly different from the mean condition nor unique in the time series during 1995–2015. In the preceding winter (January–April 1998), over the southeastern part of the Beaufort Sea, the ice was 1.5 m thinner than the mean condition on average, and the increase in ice thickness due to freezing was nearly offset by the decrease due to lateral advection, which was the result of high westward ice export and limited southerly import. The dynamic process in preceding winter was also the cause of low ice in summer 2016 according to a recent study. Model analyses suggest that the 2008 event was due to the small regional ice volume at the end of summer 2007 and ice export during the preceding fall, whereas the 2012 event was caused by the excessive summer melting.

Comparative Assessment of Different Crop Rotation Schemes for Organic Common Bean Production

The aim of the current study was to contribute to the establishment of sustainable organic crop rotation schemes for common bean under mild-winter climatic conditions. Common bean was cultivated according to organic or conventional farming practices during spring-summer in two successive years with crop and treatment during the preceding winter as either: (a) organic broccoli, (b) conventional broccoli, (c) organic faba bean used as green manure, or (d) fallow. Common bean was either inoculated with Rhizobium tropici CIAT 899 or non-inoculated, while faba bean was inoculated or non-inoculated with Rhizobium laguerreae VFLE1. Inoculating faba bean with rhizobia enhanced dry biomass production and biological N-fixing ability in both experimental years. Furthermore, organic farming did not restrict the yield of broccoli compared to conventional practices during the first year, while the reverse was the case in the second year, due to reduced soil N availability. Furthermore, green manure enhanced the fresh pod yield in the following organic crop of common bean in both years. The lowest yield was recorded in organically grown common bean when the preceding winter crop was organically grown broccoli in both years. Rhizobia inoculation of the common bean during the first year slightly increased atmospheric N fixation by common bean.

Extremely Early Summer Monsoon Onset in the South China Sea in 2019 Following an El Niño Event

The El Niño–Southern Oscillation (ENSO) is regarded as one of the most important factors for onset of the South China Sea summer monsoon (SCSSM). Previous studies generally indicated that an El Niño event tends to result in a late onset of the SCSSM monsoon. However, this relationship has not been true in recent years, particularly when an extremely early SCSSM onset (1 May 2019) occurred following the 2018/19 El Niño event in the preceding winter. The processes of the second earliest SCSSM onset in the past 41 years were investigated using NCEP–DOE reanalysis, OLR data, and ERSST. A negative sea surface temperature and associated anticyclonic anomalies were absent over the western North Pacific in the late spring of 2019 following an El Niño event in the preceding winter. Thus, the mean circulation in the late spring of 2019 does not prevent SCSSM onset, which is in sharp contrast to the composited spring of the El Niño decaying years. The convective active and westerly phases of a 30–60-day oscillation originating from the Indian Ocean provided a favorable background for the SCSSM onset in 2019. In addition, the monsoon onset vortex over the Bay of Bengal and the cold front associated with a midlatitude trough over East Asia also played important roles in triggering the early onset of the SCSSM in 2019. No tropical cyclone appeared over the western North Pacific during April and May, and the enhancement of quasi-biweekly oscillation mainly occurs after the SCSSM onset; thus, these two factors contribute little to the SCSSM onset in 2019.

Relationship between the sharp decrease in dust storm frequency over East Asia and the abrupt loss of Arctic sea ice in the early 1980s

Based on dust storm frequency (DSF) data from the China Meteorological Administration, Arctic sea-ice concentration (SIC) data from the Hadley Centre, and atmospheric reanalysis data from the National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR), temporal variations and regime shifts of East Asian DSF and Arctic SIC during 1961–2015 are revealed, and the possible relationship between them is explored. The results show that East Asian DSF in spring is closely associated with the preceding winter SIC from the northern Greenland Sea to the Barents Sea (20° W–60° E, 74.5° N–78.5° N). In the past half-century, both East Asian DSF and Arctic SIC have shown significant declining trends, with consistent regime shifts in the early 1980s. Further statistical analyses indicate that the abrupt decrease of East Asian DSF in spring may be attributed to the concurrent sharp loss of Arctic SIC in the preceding winter. It is the loss of Arctic SIC that causes the atmospheric circulation anomalies downstream by stimulating a Rossby wave train, resulting in decelerated wind speed, dampened vertical wind shear and restrained synoptic-scale disturbances over the dust source region, eventually leading to the decline in East Asian DSF over decadal timescales.

Thermal conditions and age structure determine the spawning regularities and condition of Baltic herring (Clupea harengus membras) in the NE of the Baltic Sea

Baltic herring (Clupea harengus membras) is a total spawner with a group-synchronous ovarian organization. Age polymodality in total spawners is considered an important factor in assuring that a strong population is sustainable under an intensive harvesting regime and different climatic conditions. In the present study, we investigated the seasonal and inter-annual variation in spawner age structure and the effect of preceding winter thermal conditions on the start of the herring spawning and larvae retention period. Herring spawning season in the Gulf of Riga starts up to six weeks later after colder winters compared to milder winters. Significantly older individuals dominated at the beginning of the spawning season, and thus herring mean age gradually decreased towards the end of the spawning season from 1999–2015. On an annual scale, this pattern was obvious after cold winters, while after mild winters the pattern did not continue, indicating a more homogenous maturation cycle and spawning period, despite the age and size of the herring population in mild winters. Further, herring condition factor was studied in relation to age and spawning season following different winter thermal conditions. Young, 2- and 3- year old first-spawning herring experienced significantly lower conditions after cold winters compared to older ages, indicating an age-dependent effect of preceding winter on herring maturation cycle, condition and spawning time.

Estimation of seasonal and inter-annual variations of phytoplankton in the Black Sea on the base of remote sensed data procession and chlorophyll a in situ measurements

The patterns of the seasonal and inter annual variability in the development of phytoplankton, including coc- colithophores, were studied in the northeastern part of the Black Sea in various seasons. The research was carried out on the base of remote sensed data provided by the Modis Aqua ocean color scanner and long-term ship observations. The results indicate that, in the coastal and open waters of the Black Sea, the development of phytoplankton reaches the highest level in the fall-winter and winter-spring seasons, i.e., in the periods of active winter convection. It was noted that there is a relationship between the level of coccolithophore development in the summer period and the minimal temperature of the sea surface layer in the preceding winter. The most active coccolithophore blooms, were observed after the coldest winters. Unusual winter and early spring coccolithophore blooms taking place in mild hydro meteorological conditions were registered in the Black Sea, on the base of satellite data and were confirmed by in situ measurements.