آغاز و پایان فصول طبیعی در ایران

چهار فصل طبیعی ویژگی مناطق معتدل جهان است، اما تاریخ شروع، پایان و طول مدت آنها تفاوت دارد. به منظور تعیین شروع و پایان فصول طبیعی ایران از داده های روزانه دمای ظاهری 32 ایستگاه هواشناسی سینوپتیک طی 60 سال از 1959 تا 2018 استفاده شد. شروع زمستان و تابستان به ترتیب دمای ظاهری صفر و 20 درجه، یعنی زمان توقف یا کند شدن فعالیت فیزیولوژی و مرحله زایشی در طبیعت تعیین شد. نتایج نشان داد، همه مناطق ایران چهار فصل طبیعی ندارند، بلکه مناطق ساحلی شمال و مناطق پایین تر از عرض 29 درجه جغرافیایی، فقط دو فصل پاییز (دوره خنک)و تابستان(گرم) دارند، به ترتیب سواحل شمالی، پاییز طولانی تر و تابستان کوتاه تر و مناطق جنوبی بر عکس. در دیگر مناطق ایران، به طور طبیعی چهار فصل، زمستان، بهار، تابستان و پاییز اتفاق می افتد، اما آغاز، پایان و طول مدت فصول، مرتبط با موقعیت جغرافیایی، ارتفاع و سیستم های جوی، متفاوت است. بنابراین به ترتیب از مناطق جنوبی به شمالی، آغاز زمستان 12 دی 21 آذر، بهار، 12 بهمن 18 اسفند، تابستان، 27 فروردین 30 خرداد و پاییز، 23 آبان 28 شهریور است. از طرف دیگر پایان فصول طبیعی به ترتیب، زمستان ، 11 بهمن 17 اسفند، بهار، 21 اردیبهشت 29 خرداد، تابستان، 22 آبان – 27 شهریور و پاییز، 2 اردییهشت تا 20 آذر می باشد. در مناطق معتدل ایران، طول فصول انتقالی، منظم بوده و تغییر زیادی ندارد، اما فصل تابستان و زمستان در مناطق شمال غربی و مرتفع غرب، با نظم 3 ماه در فصل، اما به طرف شرق و جنوب، طول زمستان کوتاه، و تابستان بلندتر است. چنانکه اعتدال اقلیمی از شمال غربی در همسایگی مناطق معتدل کره زمین، به شرق و جنوب کم شده و برعکس بر شباهت آن به اقلیم های بیابانی خشک جنب حاره ای گرم، مرطوب و یا سرد و خشک توران افزوده می شود. اقلیم ایران با توجه به موقعیت جغرافیایی در منطقه گذار از اقلیم معتدل به اقلیم بیابانی گرم و سرد کره زمین قرار دارد.

onset and end of natural seasons in iran

onset and end of natural seasons in iranintroduction: season is the natural pattern of change in nature, which is related to the movement of the sun, the temperature cycle, the life cycle of the earth (phenology) and human culture. in astronomical and climatic seasons, a year divided into four seasons, spring, and summer, autumn and winter (alsop, 2005), (trenberth, 1983). season is a period of the year with a homogeneous climate (alsop, 1989), that is difficult to determine exactly when to start and end. the methods of determining of the seasons are: change in the face of the earth (cayan et al, 2001), (wang et al., 2021), constant temperature threshold, (jaagus et al, 2003; determining change and starting a new season. organisms react to the onset and end of natural seasons by changing their behavior. naturally, plants and animals adjust and adapt their phonological stages to temperature changes and jumps (sparks et al, 2002), plants germinate and flower in spring,fruit in summer, reduced activity and leaf in autumn and in winter fall asleep (menzel et al, 1999 animals are also adapted to reproduction, nesting and childbirth, and their phonological period is also related to vegetation conditions. in other words, the life stages of living organisms are adapted and dependent on these natural changes (schwartz et al, 2000). some organisms also migrate in order to adapt (smith et al, 2012). the genetic response of organisms to rapid climate change and seasons associated with winter warming across the north, the early onset of spring and a long growing season is a factor in impairing the physiological response (reproduction, dormancy or migration time) of species(bradshaw et al, 2008). on the other hand, the sensible temperature of organisms is affected by radiation, wind, air temperature and humidity. as appearance temperature is an important heat factor (heat and cold) in nature, to which animals, plants and humans react. ruosteenoja et al (2019), showed the length and onset seasons of european with thresholds of 0 and 10 ° c focusing on the scenario of a 2 ° increase in temperature, an increase in summer length and a decrease in winter compared to pre industrialization. the length of summer increases by 1 degree, increases by 10 days, and the length of winters decreases by 10 to 24 days. kitowski et al, (2019), showed the onset of summer earlier, the shorter autumn, the longer summer and the shorter winter in poland with zero , 5 and 15 degree temperature fallsummerspringwinterseasonlengthendonsetlengthendonsetlengthendonsetlengthendonset8310 dec18 sep22717 sep15 apr10010 may31 jan86 30 jan11 decearlier16021 apr13 nov9012 nov19 jun10318 jun8 mar297 mar1 janlater7713356137556533936573621fluctuationconclusion: the time of the onset, end and length of natural seasons in iran are different from astronomical and calendar seasons. the slow decreasing and increasing trend of temperature at the onset and end of the seasons is initially a function of the angle of radiation and the length of day and night, but the real onset of a season with temperature jumps associated with the migratory atmospheric system (cyclone and anticyclone), siberian hypertension, it is from the north and high in the subtropics from the south. areas below 29 degree orbit in the south of iran and khuzestan and the northern coasts, have only two seasons of autumn (cool) and summer (warm) and the temperature decreases to zero and less (occurrence of winter), in the southern regions, rare and on the northern coasts is accidental and short. the apparent temperature in these areas has been decreasing since late summer and in the middle of the cold period, it is decreasing to the maximum (lowest temperature during the year) and increasing again until the onset of summer. therefore, the above areas are two periods, with a cool season and a hot and hot season. the southern coasts of iran and khuzestan have short cooling seasons and long hot and hot summers, and the northern coasts, on the contrary, have shorter summers and longer and cooler autumns, that the influence of water temperature, latitude, topography and atmospheric systems are effective in these differences. in other regions of iran, except the mentioned regions, four natural seasons occur (spring, summer, autumn and winter). in connection with the role of latitude, altitude, the arrival of migratory and high pressure siberian atmospheric systems, the time of onset, end and length of the season has a change of location. as the length of summer is more in the southern, eastern and central regions of iran and decreases in the northwest and west of iran, and the length of winter is the opposite. the length of the transitional seasons (autumn and spring) in the temperate regions of iran is not different and the three months in the season are similar to the astronomical and calendar seasons. the most important spatial difference is during winter and summer. winter decreases from three months in the northwest of iran to the south and east of iran and reaches a month in the 29 degree orbit. on the other hand, the length of summer, on the contrary, varies from five and three months from east and south of iran to northwest of iran. therefore, in temperate regions of iran, the length of natural seasons from the south and east of iran to the west and northwest of iran is more regular and approaches to three months in each season. this spatial trend indicates the climatic similarity of western and northwestern iran with temperate regions of the globe in higher latitudes and but to the center, south and east of iran, this similarity decreases and to hot and cold dry desert climate in the middle east and central asia region is similar, respectively. this indicates regularity and order in nature, which is related to the geographical principle of tobler’s law, the spatial correlation of climates and the onset, end and length of their seasons. therefore, if we consider three months in a season as a natural feature of the temperate regions of the earth and two seasons (climatic period) as a feature of the subtropical regions, iran is in the transition zone of these two climates. as from three months, the length of each season in the northwest to less than a month in the range of orbit 29 degrees, and then the subtropical conditions with two seasons (warm and cool) appear. therefore, from northwest to east and south of iran, the climatic moderation decreases and its tropical sub characteristic (longer summer and shorter winter) heat and dryness to heat and humidity in southern iran is added. naturally, in this spatial process, primarily large scale atmospheric rotations and secondly, geographical phenomena (their shape and position) play a pivotal role. the caspian