Interdecadal Variations of the March Atmospheric Heat Source over the Southeast Asian Low-Latitude Highlands

Based on the fifth-generation reanalysis dataset from the European Centre for Medium-Range Weather Forecasts for 1979–2019,we investigated the effects of the circumglobal teleconnection(CGT)on the interdecadal variation of the March atmospheric heat source(AHS)over the Southeast Asian low-latitude highlands(SEALLH).The dominant mode of the March AHS over the SEALLH features a monopole structure with an 8–11-year period.Decadal variations in the AHS make an important contribution to the 11-year low-pass filtered component of the AHS index,whichexplains 54.3%of the total variance.The CGT shows a clear interdecadal variation,which explains 59.3%of the total variance.The March AHS over the SEALLH is significantly related to the CGT on interdecadal timescales.When the CGT is optimally excited by a significant cyclonic vorticity source near northern Africa(i.e.,in its positive phase),the SEALLH is dominated by anomalous southerly winds and ascending motions on the east of the anomalous cyclone.The enhanced advection and upward transfer result in a high-enthalpy air mass that converges into and condenses over the SEALLH,leading to a largerthan-average March AHS over this region.The key physical processes revealed by this diagnostic analysis are supported by numerical experiments.

Impact of the South China Sea Throughflow on the Pacific Low-Latitude Western Boundary Current:A Numerical Study for Seasonal and Interannual Time Scales

Prior studies have revealed that,as a part of the Pacific tropical gyre,the South China Sea throughflow（SCSTF） is strongly influenced by the Pacific low-latitude western boundary current（LLWBC）.In this study,ocean general circulation model（OGCM） experiments with and without connection to the South China Sea（SCS） were performed to investigate the impact of the SCSTF on the Pacific LLWBC.These model experiments show that if the SCS is blocked,seasonal variability of the Kuroshio and Mindanao Current becomes stronger,and the meridional migration of the North Equatorial Current（NEC） bifurcation latitude is enhanced.Both in seasonal and interannual time scales,stronger Luzon Strait transport（LST） induces a stronger Kuroshio transport combined with a southward shift of the NEC bifurcation,which is unfavorable for a further increase of the LST;a weaker LST induces a weaker Kuroshio transport and a northward shifting NEC bifurcation,which is also unfavorable for the continuous decrease of the LST.

Comparison of Diurnal,Seasonal and Solar Cycle Variations of High-latitude,Mid-latitude and Low-latitude Ionosphere

Comparison of regular(diurnal,seasonal and solar cycle)variations of high-latitude,mid-latitude and low-latitude ionospheric characteristics has been provided on basis of local empirical models of the peak electron density and the peak height.The local empirical models were derived from the hand-scaled ionogram data recorded by DPS-4 digisondes located at Norilsk(69°N,88°E),Irkutsk(52°N,104°E)and Hainan(19°N,109°E)for a 6-year period from December,2002 to December,2008.The technique used to build the local empirical model is described.The primary focus is diurnal-seasonal behavior under low solar activity and its change with increasing solar activity.Both common and specific features of the high-latitude(Norilsk),mid-latitude(Irkutsk)and low-latitude(Hainan)regular variations were revealed using their local empirical models.

Characteristics of ionospheric scintillation climatology over Indian low-latitude region during the 24th solar maximum period

The amplitude and phase of L-band satellite signals are fluctuated randomly due to small scale electron density irregularity structures in the ionosphere which result in fleeting variations, known as 'ionospheric scintillations'. The Global Navigation Satellite System(GNSS) is a profound remote sensing tool to monitor, model and forecast the ionospheric weather conditions. In this paper, the GNSS amplitude scintillation data has been analyzed during the year 2013 at Bengaluru(12.9°N, 77.59°E) and Lucknow(26.8467°N, 80.9462°E) stations to reinforce climatology of ionospheric scintillation over Indian low-latitude region. The probability of scintillation occurrence and their variations over equatorial and Equatorial Ionization Anomaly(EIA) regions in India are analyzed during various geomagnetic quiet and disturbed days, months and seasons. The annual occurrence of amplitude scintillations are mapped with the function of local time. It is observed from the experimental results that the probability of scintillations occurrences is higher over EIA region than over the equatorial region. The probability of scintillations is higher during March equinox and December solstice, and lowest during June solstice.Distribution of scintillations is intense during post-sunset period. The maximum percentage of scintillation occurrences at the two stations are recorded in November. Moreover, the highest percentage of scintillation occurrences took place on storm day(March 17, 2013) at the two stations. This work would be helpful for understanding the features of GNSS amplitude scintillations over Southern and Northern Indian regions. Moreover, these kinds of investigations are helpful for developing new algorithms to nowcast and forecast ionospheric scintillations over Indian Sub-continent.

A measure of ionospheric irregularities:zonal velocity and its implications for L-band scintillation at low-latitudes

We estimate the zonal drift velocity of small-scale ionospheric irregularities at low latitude by leveraging the spaced-receivers technique applied to two GNSS receivers for scintillation monitoring installed along the magnetic parallel passing in Presidente Prudente(Brazil,magnetic latitude 12.8°S).The investigated ionospheric sector is ideal to study small-scale irregularities,being located close to the expected position of the southern crest of the equatorial ionospheric anomaly.The measurement campaign took place between September 2013 and February 2014,i.e.equinox and summer solstice seasons under solar maximum,during which the probability of formation of small-scale irregularities is expected to maximize.We found that the hourly average of the velocity increases up to 135 m/s right after the local sunset at ionospheric altitudes and then smoothly decreases in the next hours.Such measurements are in agreement with independent estimations of the velocity made by the Incoherent Scatter Radar located at the Jicamarca Radio Observatory(magnetic latitude 0.1°N),by the Boa Vista Ionosonde(magnetic latitude 12.0°N),and by applying a recently-developed empirical regional short-term forecasting model.Additionally,we investigated the relationship with the percentage occurrence of amplitude scintillation;we report that it is exponentially dependent on the zonal velocity of the irregularities that cause it.

INTERACTION BETWEEN WAVES IN LOW-LATITUDE ATMOSPHERE AND TROPICAL LOW-FREQUENCY OSCILIATION

This paper is an attempt to reveal the dynamic mechanism of low-frequency oscillation (LFO) in tropical atmosphere. A two-level model on equatorial β-plane which includes the equation of water vapor evolution and the interaction between condensational latent heating due to convection and large-scale dynamic processes is devel- oped. The difference in both heating capacity and moisture evaporation between underlying land and ocean surfaces is also taken into consideration. Firstly, the eigenmode in this model is analysed to reveal the effect of convective heating on equatorial waves. It is found that with this heating, all the waves including Kelvin waves, Rossby waves, gravity waves and mixed Rossby-gravity waves, are slowed down, thus frequency differences between fast and slow waves are reduced. Therefore these waves are more likely to interact with each other, causing the perturbations to propagate eastward very slowly and producing LFO. The comparison between results of dry and moist model integration has confirmed the conclusion from dynamic analysis.

A SIMPLE NONLINEAR MODEL OF INERTIAL OSCILLATION OF ATMOSPHERE IN LOW-LATITUDES

In this paper,by simplifying the governing equation in low latitudes a nonlinear model which takes into consideration the equatorial β-plane approximation and describes the natural oscillation of the atmosphere has been set up.By applying this model the following results are shown: (1)There exists the pure inertial oscillation only in u_0>0(westerly current),the angular frequency of linear oscillation of y is ω_0~*=(β_0u_0~*)^(1/2),the corresponding oscillatory period is 1—2 weeks.There are two kinds of angular frequencies under the nonlinear condition,the one is ω_0=(β_0u_0)^(1/2)the other is ω_1= 1/2 β_0y_0.When a soliton oscillator occurs(ω_1=ω_0),the oscillatory period increases rapidly,and T→∞. (2)When the pressure field is considered,the oscillation exists not only in u_0>0(westerly current) but also in u_0<0(weak easterly current).However this weak pressure field has slight effect on the oscillatory period. (3)The stability of inertial oscillation depends on the linear inertial parameter μ.As the parameter μ changes sign from negative to positive,the supercritical bifurcation takes place in b<0.

The influence of human activity and precipitation change on mid-long term evolution of landslide and debris flow disasters

After defining landslide and debris flow, human activity, and precipitation indices, using with landslide and debris flow disaster data in low-latitude plateau of China, reflecting human activity and precipitation data, the influence of human activity and precipitation on mid-long term evolution of landslide and debris flow was studied with the wavelet technique. Results indicate that mid-long evolution of landslide and debris flow disaster trends to increase 0.9 unit every year, and presents obvious stage feature. The abrupt point from rare to frequent periods took place in 1993. There is significant in-phase resonance oscillation between human activity and landslide and debris flow frequency on a scale of 11-16 years, in which the variation of human activity occurs about 0.2-2.8 years before landslide and debris flow variation. Thus, the increase of landslide and debris flow frequency in low latitude plateau of China may be mainly caused by geo-environmental degradation induced by human activity. After the impact of human activity is removed, there is sig- nificant in-phase resonance oscillation between landslide and debris flow frequency and summer rainfall in low-latitude plateau of China in quasi-three-year and quasi-six-year scales, in which the variation of summer precipitation occurs about 0.0-0.8 years before landslide and debris flow variation. Summer precipitation is one of important external causes which impacts landslide and debris flow frequency in low-latitude plateau of China. The mid-long term evolution predicting model of landslide and debris flow disasters frequency in low-latitude plateau region with better fitting and predicting ability was built by considering human activity and summer rainfall.

Some Topics on the Auroras in Middle and Low Latitudes

This paper consists of the following topics: (1) Significance of observing lower-latitude auroras. (2) Different kinds of atmospheric luminosity. (3) Chronological catalogues and maps of isochasms for auroral visibility. (4) Analysis of archaeo-auroras in low latitudes during earlier centuries. (5) Aurora observing studies since International Geophysical Year (IGY). (6) Concerning prediction of auriora occurrence.

中新世气候适宜期构造运动加速全球海洋碳循环

Global warming during the Miocene Climate Optimum(MCO,~17-14 million years ago)is associated with massive carbon emissions sourced from the flood basalt volcanism and ocean crustal production.However,the perturbation of tectonic carbon degassing on the interaction between climate change and carbon cycle remains unclear.Here,through time-evolutive phase analysis of new and published high-resolution benthic foraminiferal oxygen(δ^(18)O)and carbon(δ^(13)C)isotope records from the global ocean,we find that variations in the marine carbon cycle lead the climate-cryosphere system(δ^(13)Clead-δ^(18)O)on 405,000-year eccentricity timescales during the MCO.This is in contrast to the previously reported climate-lead-carbon(δ^(18)O-lead-δ^(13)C)scenario during most of the Oligo-Miocene(~34-6 million years ago).Further sensitivity analysis and model simulations suggest that the elevated atmospheric CO_(2) concentrations and the resulting greenhouse effect strengthened the low-latitude hydrological cycle during the MCO,accelerating the response of marine carbon cycle to eccentricity forcing.Tropical climate processes played a more important role in regulating carbon-cycle variations when Earth's climate was in a warm regime,as opposed to the dominant influence of polar ice-sheet dynamics during the PlioPleistocene(after~6 million years ago).

Circulation in the western tropical Pacific Ocean and its seasonal variation

An assimilation data set based on the GFDL MOM3 model and the NODC XBT data set is used to examine the circulation in the western tropical Pacific and its seasonal variations. The assimilated and observed velocities and transports of the mean circulation agree well. Transports of the North Equatorial Current (NEC), Mindanao Current (MC), North Equatorial Countercurrent (NECC) west of 140°E and Kuroshio origin estimated with the assimilation data display the seasonal cycles, roughly strong in boreal spring and weak in autumn, with a little phase difference. The NECC transport also has a semi-annual fluctuation resulting from the phase lag between seasonal cycles of two tropical gyres’ recirculations. Strong in summer during the southeast monsoon period, the seasonal cycle of the Indonesian throughflow (ITF) is somewhat different from those of its upstreams, the MC and New Guinea Coastal Current (NGCC), implying the monsoon’s impact on it.

Hydroclimate changes related to thermal state of the tropical Pacific in the northern coast of the South China Sea since~8000 cal yr B.P.

Under the complex influences including the monsoonal climates and tropical hydrological cycle,the features and forcing mechanisms of precipitation changes in the tropical monsoon regions remain controversial.The northern coast of the South China Sea(NCSCS),connecting the South China Sea(SCS)and the Pearl River Estuary(PRE),is a critical area providing reliable tropical precipitation records and probing the possible forcing mechanism of tropical precipitation,benefitted from its high deposition rate and hydroclimatic sensitivity.Here,δ^(18)O variations of planktonic(δ^(18)O_(G).ruber)and benthic foraminifera(δ^(18)O_(C).lobatulus)were investigated respectively to reconstruct a high-resolution low-latitude precipitation record from the core 17NH-NC3 in the NCSCS.The results show a distinctδ^(18)O difference betweenδ^(18)O_(G).ruber andδ^(18)O_(C).lobatulus,not only with respect to values,but also with respect to trends in some time intervals.The clear difference between the planktonic and benthic foraminifera(Δδ^(18)O_(b-p))illustrates the significant vertical salinity stratification.And the temporal trend ofΔδ^(18)O_(b-p) indicates the degree of salinity stratification variated since the mid-Holocene.We assume that the degree of stratification in the NCSCS was mainly controlled by tropical precipitation changes.Thus,the trend ofΔδ^(18)O_(b-p) values could indicate the temporal change of the tropical precipitation.The precipitation record of our research area is closely related to the tropical atmosphere–ocean dynamics stimulated by sea surface temperature(SST)changes of the tropical Pacific zone,analogous to the El Niño–Southern Oscillation(ENSO)events.During the mid-Holocene(from 8260 to 5180 cal yr B.P.),the sustainable higherΔδ^(18)O_(b-p) values(>1.23‰)suggested a large amount of precipitation,pointing to a sustained state of La Niña-like,which is associated with lasted higher difference between Western SST and Eastern SST(W-E SST gradient)in the equatorial Pacific.Since 5180 cal yr B.P.,the decreasingΔδ^(18)O_(b-p) indicates less low-latitude precipitation,which can be ascribed to an El Niño-like mean state arising from decreased W-E SST gradient.Our study provides a new continuous high-resolution archive of low-latitude precipitation in the tropical monsoon region since 8260 cal yr B.P.And this record highlights that the thermal state of the tropical Pacific most likely adjusted the low-latitude precipitation since the mid-Holocene.

Agronomic assessment of two populations of intermediate wheatgrass—Kernza^(®)(Thinopyrum intermedium)in temperate South America

Background Kernza®intermediate wheatgrass is a perennial grain and forage crop that can provide several ecosystem services.Major research efforts focused on Kernza have taken place in high latitudes.The goal of this study was to evaluate,for the first time,the agronomic performance of Kernza in a low-latitude region with mild winters.Methods A KS-cycle 4 Kernza population(A)was planted in spring in Wisconsin,USA,and selected in one cycle for lower vernalization requirements,obtaining a new population(B).These two populations,at three nitrogen(N)fertilization rates,were evaluated in a full factorial,completely randomized field experiment in Uruguay over 2 years.Results The populations were similar in grain yields and flowering time in the 1st year,but population B had 63%lower grain yield in the 2nd year and 20%lower forage yield throughout the experiment.Increasing the N rate to 160 kg ha−1 led to a 63%increase in grain yield and 28%increase in forage yield across populations.Forage yields and nutritive values were similar to those reported in the northern hemisphere.However,grain yields for both the 1st(316 kg ha−1)and 2nd year(41 kg ha−1)were lower due to reduced flowering and weed competition.Conclusions Expansion of Kernza to lower-latitude regions will require further breeding to improve reproductive performance.