The high-latitude ionospheric phenomena observed by DPS-4 at Zhongshan Station, Antarctica

Ionograms, which were obtained from February 1995 to January 1999 by a Digisonde Portable Sounder-4 (DPS-4) at Zhongshan Station in Antarctica, have been scaled. The ionograms interpretation has shown various ionosphcric phcnomena occurred in the cusp region. They are particle precipitation effects in the E region. F region magnetic noon phenomena, slant Es phenomena and lacuna. F layer irregularity zone (FLIZ) phenomena, and auroral oval identification. Typical examples of ionograms and ionogram sequences observed at Zhongshan Station are displayed in this paper.

In situ detection of the electron diffusion region of collisionless magnetic reconnection at the high-latitude magnetopause

Magnetic reconnection is the most fundamental energy-transfer mechanism in the universe that converts magnetic energy into heat and kinetic energy of charged particles.For reconnection to occur,the frozen-in condition must break down in a localized region,commonly called the ‘diffusion region'.In Earth's magnetosphere,ion diffusion regions have already been observed,while electron diffusion regions have not been detected due to their small scales(of the order of a few km)(Paschmann,2008).In this paper we report,for the first time,in situ observations of an active electron diffusion region by the four Cluster spacecraft at the Earth's highlatitude magnetopause.The electron diffusion region is characterized by nongyrotropic electron distribution,strong field-aligned currents carried by electrons and bi-directional super-Alfvénic electron jets.Also observed were multiple micro-scale flux ropes,with a scale size of about 5 c/ω_(pe)(12 km,with c/ωpe the electron inertial length),that are crucial for electron acceleration in the guide-field reconnection process(Drake et al.,2006 a).The data demonstrate the existence of the electron diffusion region in collisionless guide-field reconnection at the magnetopause.

Model Simulation of Artificial Heating of the Daytime High-Latitude F-Region Ionosphere by Powerful High-Frequency Radio Waves

The large-scale disturbance of the spatial structure of the daytime high-latitude F-region ionosphere, caused by powerful high-frequency radio waves, pumped into the ionosphere by a groundbased ionospheric heater, is studied with the help of the numerical simulation. The mathematical model of the high-latitude ionosphere, developed earlier in the Polar Geophysical Institute, is utilized. The mathematical model takes into account the drift of the ionospheric plasma, strong magnetization of the plasma at F-layer altitudes, geomagnetic field declination, and effect of powerful high-frequency radio waves. The distributions of the ionospheric parameters were calculated on condition that an ionospheric heater, situated at the point with geographic coordinates of the HF heating facility near Tromso, Scandinavia, has been operated, with the ionospheric heater being located on the day side of the Earth. The results of the numerical simulation indicate that artificial heating of the ionosphere by powerful high-frequency waves ought to influence noticeably on the spatial structure of the daytime high-latitude F-region ionosphere in the vicinity of the ionospheric heater.

Endocrine response of early-hatching Asian Short-toed Lark nestlings exposed to cold temperature in a high-latitude grassland habitat

Background:In high latitude grassland habitats,altricial nestlings hatching in open-cup nests early in the breeding season must cope with cold temperature challenges.Thyroid hormones(triiodothyronine,T_(3)and thyroxine,T_(4))and corticosterone play a crucial role in avian thermoregulation response to cold.Investigating the endocrine response of altricial nestlings to temperature variation is important for understanding the adaptive mechanisms of individual variation in the timing of breeding in birds.Methods:We compared nest temperature,ambient temperature,body temperature,plasma T_(3),T_(4)and corticosterone levels in Asian Short-toed Lark(Alaudala cheleensis)nestlings hatching in the early-,middle-,and late-stages of the breeding season in Hulunbuir grassland,northeast China.Results:Mean nest temperature in the early-,middle-and late-stage groups was-1.85,3.81 and 10.23℃,respectively,for the 3-day-old nestlings,and 6.83,10.41 and 11.81℃,respectively,for the 6-day-old nestlings.The nest temperature significantly correlated with body temperature,plasma T_(3),T_(4)and corticosterone concentrations of nestlings.Body temperature of 3-day-old nestlings in the early and middle groups was significantly lower than that of the late group,but there was no significant difference between the nestlings in the early and middle groups.The T_(4)and T_(3)concentrations and the ratio of T_(3)/T_(4)of both 3-and 6-day-old nestlings in the early-stage group were significantly higher compared to the middle and late groups.The corticosterone levels of 3-day-old nestlings were significantly higher in the early-stage group compared to the middle-and late-stage groups.Conclusion:Nestlings hatching early responded to cold temperature by increasing thyroid hormones and corticosterone levels even in the early days of post hatching development when the endothermy has not been established.These hormones may play a physiological role in neonatal nestlings coping with cold temperature challenges.

The global response of temperature to high-latitude vegetation greening in a two-dimensional energy balance model

The relationship between vegetation greening and climate change remains unclear due to its complexity, especially in drylands. Against the background of global warming, arid and semi-arid areas, including mid-latitude deserts, are most sensitive to climate change. In recent decades, the mechanisms underlying the relationship between vegetation greening and climate change have been widely discussed in the literature. However, the influence of vegetation greening in high latitudes on regional climate has not been fully studied. In this paper, a two-dimensional energy balance model was used to study the influence of greening in high latitudes on mid-latitude deserts. The authors found that when greening occurs in high latitudes, the mid-latitude desert recedes at the south boundary, while the polar ice belt and low-latitude vegetation belt both expand. Simultaneously, greening in high latitudes can induce a negative temperature anomaly in northern latitudes and a positive temperature anomaly in southern latitudes. The mid-latitude desert expands at its north and south boundaries until the CO2 concentration reaches 600 ppm(saturated state). The greening in high latitudes could result in a lower global-mean temperature in the ‘saturated’ state, due to the stronger cooling in high latitudes.

SuperDARN CUTLASS Finland radar observations of high-latitude magnetic reconnections under northward interplanetary magnetic field (IMF) conditions

A number of backscatter power enhancement events with ＂equatorward-moving radar auroral forms＂ in the high-latitude ionosphere were observed by SuperDARN CUTLASS Finland radar when the IMF was northward during 09：00 -10：00 UT on 26 March 2004. These events were also associated with sunward flow enhancements at each location in the Northern Hemisphere which were shown in ionospheric convections measured by the SuperDARN radars. These are typical features of high-latitude （lobe） magnetic reconnections. The durations of the velocity enhancements imply that the evolution time of the lobe reconnec- tions is about 8-16 rain from their origin at the reconnection site to their addition to the magnetotall lobe again. In additional, the Double Star TC-1 spacecraft was moving from magnetosheath into magnetosphere, and crossing the magnetopause near the subsolar region during this interval, and observed typical low-latitude magnetic reconnection signatures. This infers that the dayside high- and low-latitude reconnections may occur simultaneously.

An Investigation of Optimal Machine Learning Methods for the Prediction of ROTI

The rate of the total electron content(TEC)change index(ROTI)can be regarded as an effective indicator of the level of ionospheric scintillation,in particular in low and high latitude regions.An accurate prediction of the ROTI is essential to reduce the impact of the ionospheric scintillation on earth observation systems,such as the global navigation satellite systems.However,it is difficult to predict the ROTI with high accuracy because of the complexity of the ionosphere.In this study,advanced machine learning methods have been investigated for ROTI prediction over a station at high-latitude in Canada.These methods are used to predict the ROTI in the next 5 minutes using the data derived from the past 15 minutes at the same location.Experimental results show that the method of the bidirectional gated recurrent unit network(BGRU)outperforms the other six approaches tested in the research.It is also confirmed that the RMSEs of the predicted ROTI using the BGRU method in all four seasons of 2017 are less than 0.05 TECU/min.It is demonstrated that the BGRU method exhibits a high level of robustness in dealing with abrupt solar activities.

Identification of optical auroras caused by mantle precipitation with the aid of particle observations from DMSP satellites

Particle observations of the Defense Meteorological Satellite Program(DMSP) show that discrete auroral structures commonly exist in the region of the plasma mantle, but the optical features of the aurora generated by particles from the plasma mantle(called ‘mantle aurora’ in this paper) have not been established. A comparison of 7-year optical auroral observations made at the Yellow River Station with conjugate particle observations obtained from the DMSP confirm that mantle auroras have common features and can be clearly identified from all-sky imager observations. The mantle auroras normally present as sporadic and weak auroral structures split poleward of the dayside auroral oval. They are observed in both the green and red lines with the intensity of the red line being greater than that of the green line. In this paper, we illustrate typical mantle auroras and provide statistics on 55 mantle aurora cases that are confirmed by particle observation by the DMSP. Statistical results show that the occurrence of the mantle aurora has no clear dependence on the IMF By and Bz conditions, but the motion of the mantle aurora strongly depends on the IMF By, which indicates that the generation of the mantle aurora is intimately related to the dayside magnetopause reconnection. With the fundamental criteria for distinguishing the mantle aurora presented in this paper, we will be able to independently identify the mantle auroras from ground optical observations. This will allow us to investigate the physical processes that occur in the plasma mantle by monitoring the evolution of the auroral forms.

The effect of the feedback cycle between the soil organic carbon and the soil hydrologic and thermal dynamics

Biogeochemical feedback processes between soil organic carbon (SOC) in high-latitude organic soils and climate change is of great concern for projecting future climate. More accurate models of the SOC stock and its dynamics in organic soil are of increasing importance. As a first step toward creating a soil model that accurately represents SOC dynamics, we have created the Physical and Biogeochemical Soil Dynamics Model (PB-SDM) that couples a land surface model with a SOC dynamics model to simulate the feedback cycle of SOC accumulation and thermal hydrological dynamics of high-latitude soils. The model successfully simulated soil temperatures for observed data from a boreal forest near Fairbanks, and 2000 year simulations indicated that the effect of the feedback cycle of SOC accumulation on soil thickness would result in a significant differences in the amount of SOC.

Dominant Factors of the Nature Regulating CO2 Release from Boreal Forest Land

Temperature is often considered as a primary factor for microbial decomposition of soil organic carbon. Boreal forests are the large terrestrial carbon pool: if carbon stored in this region is transferred to the atmosphere as CO2 by a warming-induced acceleration of its decomposition, there will be positive feedback to global warming. It is reported that real issue regarding the release of carbon from soils to the atmosphere is how natural factors interact to influence decomposition of soil organic matter, so we observed mass losses (indicating decomposition rates) from litter and litterfall in a Northern Fennoscandia forest over 3 years under natural conditions. Our field survey has demonstrated that mass losses from most kinds of sample had moderate correlation with the temperature. Of the various samples, the canopy-gap litter alone had a greater rate (~70%) of mass loss. It is at least necessary to make a clear distinction of monitoring sites (under the canopy and in the canopy gap) when discussing the effect of climate on soil CO2 release from high-latitude forests. Though temperature, soil moisture and soil properties are prioritized in the issue of soil CO2 release, our results suggest that the fungi/bacteria rate and the wind-related mix/fragmentation are also important factors to be considered;however, this speculation is just tentative, and more detail research is called for.

青藏高原地表变暗与北极气候变化间的共振

The Tibetan Plateau(TP)exerts a profound influence on global climate over million-year timescales due to its past uplift.However,whether the ongoing climate changes over the TP,particularly the persistent reduction in its local albedo(referred to as“TP surface darkening”),can exert global impacts remains elusive.In this study,a state-of-the-art coupled land–atmosphere global climate model has been employed to scrutinize the impact of TP darkening on polar climate changes.Results indicate that the projected TP darkening has the potential to generate a stationary Rossby wave train,thereby modulating the atmospheric circulation in the high-latitudes of the Northern Hemisphere and instigating a dipole-like surface air temperature anomaly pattern around the Arctic region.An additional experiment suggests that the projected Arctic warming may in return warm the TP,thus forming a bi-directional linkage between these two climate systems.Given their association with vast ice reservoirs,the elucidation of this mechanism in our study is crucial in advancing our comprehension of Earth system climate projections.