Season Transition Period Research Articles

Dust storm-driven dispersal of potential pathogens and antibiotic resistance genes in the Eastern Mediterranean.

The atmosphere hosts a microbiome that connects distant ecosystems yet remains relatively unexplored. In this study, we tested the hypothesis that dust storms enhance the spread of pathogenic microorganisms and whether these microorganisms carry antibiotic resistance and virulence-related genes in the Eastern Mediterranean. We collected air samples during a seasonal transition period, capturing data from 13 dusty days originating from Middle Eastern sources, including the Saharan Desert, Iraq, Iran, and Saudi Arabia, and 32 clear days, with temperatures ranging from 16.5 to 27.1°C. Using metagenomic analysis, we identified several facultative pathogens like Klebsiella pneumoniae, Stenotrophomonas maltophilia, and Aspergillus fumigatus, which are linked to human respiratory diseases, and others like Zymoseptoria tritici, Fusarium poae, and Puccinia striiformis, which are harmful to wheat. The abundance of these pathogens increased during dust storms and with rising temperatures. Although we did not find strong evidence that these species harbored antibiotic resistance or virulence-related genes, which could be linked to their pathogenic potential, dust storms transported up to 125 times more total antibiotic resistance genes, as measured by RPKM abundance, compared to clear conditions. These levels during dust storms far exceeded those found in other ecosystems. While further research is needed to determine whether dust storms and temperature variations pose an immediate threat to public health and the environment, our findings underscore the importance of continuous monitoring of atmospheric microbiomes. This surveillance is crucial for assessing potential risks to human health and ecosystem stability, particularly in the face of accelerating global climate change.

Nutrients retention function indications in the water quality of the floodplain area on the lower Batanghari River

The Lower Batanghari River often experiences mass deaths of fish. This could be a symptom of eutrophication caused by nutrient enrichment in the water bodies. Floodplain areas are important in reducing parts of these nutrient loadings. This study aimed to examine water qualities related to the nutrient retention function within the Batanghari River floodplain ecosystem. A sampling expedition was conducted in April-May 2021, during a dry season transition period. Sampling was conducted at 20 sampling points stretching over +200 km long within the river and its tributaries. These sampling points were categorized as main river channels, tributaries, and floodplain swamps and lakes. The water quality parameters measured were temperature, pH, conductivity, dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP), and total organic matter (TOM). The main river TP concentrations ranged from 0.21-0.33 mg/L, suitable for fishery activities. The overall sampling point groups have distinct characteristics regarding their DO, TP, and TOM values. The average TP in floodplain lakes was found significantly lower (t(13)=8.636, p<0.05) than in the river. Meanwhile, a decrease in TN up to 90% was also found in its lower main river channel. These lower nutrient concentrations along the river floodplain gradients indicate a nutrient retention function. Thus, to reduce eutrophication impacts, floodplain conservation is becoming important.

¿Where do migratory fish spawn in a neotropical Andean basin regulated by dams?

Spawning sites play a key role in the reproduction of fish allowing populations to endure over time. The Nechí River is an important spawning area for potamodromous fish species where one of the threats is dam construction. In order to determine the importance of the Nechí River as a spawning site in the Magdalena River basin, sampling was conducted during the low-water-to-high-water season transition period between 2018 and 2019 at seven sampling sites. The average density of ichthyoplankton was 42.4 ind.10m-3 (SD = 7.1). Of the individuals in the post-larval stage, seven migratory species were identified, and two additional taxa were identified to genus; Prochilodus magdalenae, Megaleporinus muyscorum, and Pseudoplatystoma magdaleniatum presented the greatest density. At the temporal level, the greatest density of larvae of potamodromous species was observed in the first high-water season of 2019 with a total of 5.7 ind.10m-3(SD = 1.044), of which the most representative at the seasonal level were the Cauca River, Magdalena River, and Nechí River before it flows into the Cauca River. There were significant differences in the frequency of embryos and vitelline larvae of the potamodromous species in the interaction of the sampling sites and high-water seasons, as well as with the density of post-larvae. The average drift distance of the spawning areas is roughly 52.1 km. A positive association was found between the volume of turbined water and the presence of ichthyoplankton in the Porce River site, after discharge from the Porce III Hydroelectric Plant. The Nechí River is an important spawning site and there seems to be an association between the increase in ichthyoplankton densities and the distance to the dam (Porce III) as long as there are floodplains along the course of the river.

Footprints of El Niño La Niña on the evolution of particulate matter over subtropical Island Taiwan

Particulate matter (PM) pollution has become a major problem worldwide, with significant adverse health impacts, but the climatology of annual variations in and the effect of climate change on PM levels are still not comprehensively evaluated. Here we show that the vertical motions of the East Asian winter and summer monsoons regulate the annual variation in PM over Taiwan. The PM pollution season starts and ends earlier during El Niño episodes than during La Niña episodes. Furthermore, the onset, active, break, revival, and retreat phases of the PM pollution lifecycle are innovatively defined. Our results demonstrate that the annual seasonal cycle dominates wintertime PM pollution climate development during the active phase with a minor modulation by El Niño and La Niña episodes, whereas October and March, the seasonal transition periods, are significantly modulated by these two episodes. The findings suggest a new dimension of PM pollution research—the lifecycle evolution effect.

The role of Weather Modification Technology for forest and land fire disaster mitigation in the perspective of carbon emission reduction in Indonesia

This paper reviews the effectiveness of implementing Weather Modification Technology (WMT) in efforts to control forest and land fire disasters in Indonesia. Analysis is carried out on several parameters in the field that can be measured and observed. WMT has been proven to be able to increase rainfall intensity by 12.9% and shorten the duration of Consecutive No Rain Days, which in turn can reduce the number of hotspot events in the target area. The implementation of WMT during the rainy season transition period has also been proven to be able to increase the peatland groundwater level, which ultimately shortens the drought period in the target area. The WMT implementation program, which has become increasingly well-planned in the last 4 years (2020-2023), has proven to be able to reduce the number of hotspot incidents, the extent of forest and land fires, and the amount of carbon emissions in Indonesia quite significantly. Based on updated data until September 2023, the number of hotspots, burnt area, and total carbon emissions in Indonesia were "only" 22%, 38.9%, and 5.3% respectively compared to the numbers in 2019, which was both an El Nino year.

Daily time series of river water levels derived from a seasonal linear model using multisource satellite products under uncertainty

Satellite altimetry helps to monitor continental water levels with global coverage and near-real time accessibility. However, a main drawback of satellite altimetry is its low acquisition frequency that hinders the use of altimeters in flood forecasting or reservoir operation processes. This study provides a new method to estimate daily river heights from multisource hydro-climate satellite products without using ground-based data. First, the approach develops a simple statistical model, a seasonal linear model, using satellite altimetry, land surface temperature (LST), satellite precipitation and satellite soil moisture products. Second, a Monte Carlo simulation is used to understand the model accuracy by attributing the model output errors to uncertainties from the multiple satellite products. For the first aim, the study shows that using high-frequency satellite data to improve the temporal resolution of the satellite radar altimetry is better than an approach merging multiple satellite altimetry data. With respect to the second objective, it is found that higher variances are found in seasonal transition periods where there are significant changes in satellite observations. The overall error of the model is attributed to both uncertainties of satellite input data and the interactions among their uncertainties. The results demonstrate the capability of using multisource satellite data to predict daily time series of river heights in data-poor areas. The results also highlight the importance of quantifying uncertainty to increase the reliability of flood forecasting models using satellite products.

Seasonal soil nitrogen dynamics affect yields of lowland rice in the savanna zone of West Africa

AbstractBackground: Rice production in low‐input systems of West Africa relies largely on nitrogen supply from the soil. Especially in the dry savanna agro‐ecological zone, soil organic N is mineralized during the transition period between the dry and the wet seasons. In addition, in the inland valley landscape, soil N that is mineralized on slopes may be translocated as nitrate into the lowlands. There, both in‐situ mineralized as well as the laterally translocated nitrate‐N will be exposed to anaerobic conditions and is thus prone to losses.Aim: We determined the dynamics of soil NO3‐N along a valley toposequence during the dry‐to‐wet season transition period and the effects of soil N‐conserving production strategies on the grain yield of rainfed lowland rice grown during the subsequent wet season.Methods: Field experiments in Dano (Burkina Faso) assessed during two consecutive years the temporal dynamics and spatial fluxes of soil nitrate along a toposequence. We applied sequential and depth‐stratified soil nitrate analysis and nitrate absorption in ion exchange resin capsules in lowlands that were open to subsurface interflow and in those where the interflow from the was intercepted. During one year only we also assessed the effect of pre‐rice vegetation on conserving this NO3‐N as well as on N addition by biological N2 fixation in legumes using δ15N isotope dilution. Finally, we determined the impact of soil N fluxes and their differential management during the transition season on growth, yield and N use of rainfed lowland rice.Results: Following the first rainfall event of the season, soil NO3‐N initially accumulated and subsequently decreased gradually in the soil of the valley slope. Much of this nitrate N was translocated by lateral sub‐surface flow into the valley bottom wetland. There, pre‐rice vegetation was able to absorb much of the in‐situ mineralized and the laterally‐translocated soil NO3‐N, reducing its accumulation in the soil from 40–43 kg N ha−1 under a bare fallow to 1–23 kg N ha−1 in soils covered by vegetation. Nitrogen accumulation in the biomass of the transition season crops ranged from 44 to 79 kg N ha−1 with a 36–39% contribution from biological N2 fixation in the case of legumes. Rice agronomic performance improved following the incorporation as green manure of this “nitrate catching” vegetation, with yields increasing up to 3.5 t ha−1 with N2‐fixing transition seasons crops.Conclusion: Thus, integrating transition season legumes during the pre‐rice cropping niche in the prevailing low‐input systems in inland valleys of the dry savanna zone of West Africa can temporarily conserve substantial amounts of soil NO3‐N. It can also add biologically‐fixed N, thus contributing to increase rice yields in the short‐term and, in the long‐term, possibly maintaining or improving soil fertility in the lowland.

PSII-9 Drylot weaned calves at dry-to-rainy transition and rainy season and their effects on the growing phase

Abstract The objective of this study was to determine the best nutritional strategy for weaned calves at dry-to-rainy transition and rainy season and their effects on the growing phase. One hundred sixteen Nellore weaned males (initial BW of 173±23 kg; 10 months) were used in a randomized complete block design (blocked by BW) in a 2×2 factorial arrangement of treatments (divided in 12 lots with 9 or 10 animals/lot). Factor 1 was the strategy in the dry-to-rainy season transition (period I; pasture vs. drylot) and factor 2 was the strategy for the rainy season [period II; mineral salt ad libitum (MS) vs. supplement 3 g/kg BW]; consisting of four treatments: pasture in period I and MS in period II; pasture in period I and protein-energy supplement in period II (PEII); drylot in period I and mineral salt in period II; drylot in period I and PEII. At period I, all animals received a protein-energy supplementation (5 g/kg BW). The experiment lasted 244 days. Data were analyzed using the PROC MIXED of SAS. In period I, animals from drylot had highest final BW and ADG (P &amp;lt; 0.01; Table 1). There was no interaction among factors (P ≥ 0.772) in period II. In period II, ADG and carcass gain were highest from pasture animals (P &amp;lt; 0.01). Final BW and HCW were similar (P &amp;gt;0.788) at the end of period II, showing that animals recovery BW. Among strategies at rainy season, animals fed PEII had greater final BW and ADG (P &amp;lt; 0.01). Overall growing phase, HCW and carcass gain were greater for animals fed PEII (P &amp;lt; 0.01). Regardless of the strategy used in the dry-to-rainy season transition, animals were able to equalize final BW at the end of growing phase. In addition, protein-energy supplement at rainy season improves animal performance at the end of growing phase.

Bank erosion in a macrotidal tropical river: Exploring the relative impact of boat wash on riverbank erosion

AbstractMacrotidal tropical rivers are dynamic systems where wet‐season floods and tidal flows cause significant riverbank erosion and sediment transport. This study aimed to explore patterns of riverbank erosion and deposition in a large, tropical, macrotidal river in Northern Australia; the Daly River. In particular, we aimed to determine if recreational boat use was impacting bank erosion in this dynamic river. Erosion pins were installed at multiple levels on both banks at 10 sites along a 34 km reach of the river. Measurements were made every four to six weeks during the low water dry season, and opportunistically during the wet season (flooding period) and seasonal transition periods. A bank geotechnical assessment, riverbed cross‐sections and site bathymetry were undertaken. Whilst the wet season was a period of substantial erosion (mean rate of 0.64 mm day−1), the highest mean erosion rate (3.6 mm day−1) was observed in the early dry season (April to May), a period of stabilizing water levels but greatest boat traffic. Bank erosion at this time was measured on both sides of the river and the inside of meander bends, which is atypical of normal riverine bank erosion patterns, and indicative of erosion due to boat wash. As the dry season progressed, significant spatial differences in erosion rates were evident, where erosion was observed at sites upstream of a large shallow sand bar, while sites downstream from the sand bar gained material through the deposition of tidally transported sediment. This study highlights the importance of understanding the significance and interaction of various erosive factors in tropical tidal rivers and has demonstrated that boat wash may be an important contributor to dry season bank erosion in these systems. We encourage management agencies to consider the role of boats in any future river management program in these systems.

Heavy Rainfall Events over Central Oahu under Weak Wind Conditions during Seasonal Transitions

AbstractShort-lived afternoon heavy rainfall events may form over central Oahu during seasonal transition periods (June and October) under favorable large-scale settings. These include a deep moist layer with relatively high precipitable water (&gt;40 mm), blocking pattern in midlatitudes with a northeast–southwest moist tongue from low latitudes ahead of an upper-level trough, absence of a trade wind inversion, and weak (&lt;3 m s−1) low-level winds. Our high-resolution (1.5 km) model results show that immediately before the storm initiation, daytime land surface heating deepens the mixed layer over central Oahu and the top of the mixed layer reaches the lifting condensation level. Meanwhile, the development of onshore/sea-breeze flows, driven by land–sea thermal contrast, brings in moist maritime air over the island interior. Finally, convergence of onshore flows over central Oahu provides the localized lifting required for the release of instability. Based on synoptic and observational analyses, nowcasting with a lead time of 2–3 h ahead of this type of event is possible. In the absence of orographic effects after removing model topography, processes that lead to heavy rainfall are largely unchanged, and subsequent development of heavy showers over central Oahu are still simulated. However, when surface heat and moisture fluxes are turned off, convective cells are not simulated in the area. These results indicate that daytime heating is crucial for the development of this type of heavy rainfall event under favorable large-scale settings.

Improving the seasonal prediction of Northern Australian rainfall onset to help with grazing management decisions

The development of the Australian Community Climate and Earth-System Simulator-Seasonal prediction system version 1 (ACCESS-S1) signifies a major step towards addressing predictive limitations in multi-week to seasonal forecasting throughout Australia. It is anticipated that moving to ACCESS-S1 will provide improved skill in rainfall prediction during the dry to wet season transition period across tropical northern Australia. This is an important time for northern Australian livestock producers in terms of the decisions they make around pasture and livestock management. This study quantifies the hindcast skill of ACCESS-S1 for the northern rainfall onset (NRO), defined as the date when 50 mm of precipitation has accumulated at a given location from the 1st of September, heralding the shift towards greener pastures. We evaluate the raw model hindcasts, and compare them to hindcasts corrected for mean biases and those calibrated against observations. It is found that the raw ACCESS-S1 hindcasts broadly replicate the observed median NRO over the period 1990–2012, despite a tendency for earlier than observed onsets. In terms of forecasting the interannual variability of the NRO, the calibrated hindcasts show the greatest skill, with the largest improvements over a climatological forecast in their probabilistic forecasts of an earlier or later than usual onset, with a large portion of northern Australian showing more than 10% improvement. With real-time NRO forecasts now generated by ACCESS-S1, it is expected that the calibrated predictions will help northern Australian graziers make better informed decisions around livestock management prior to the wet season.

Seasonal herbage accumulation, plant-part composition and nutritive value of signal grass &lt;i&gt;(Urochloa decumbens)&lt;/i&gt; pastures under simulated continuous stocking

In order to optimize the regrowth and harvest of signal grass (Urochloa decumbens) cv. Basilisk pastures it is necessary to establish more precise grazing management guidelines. The objective of this study was to evaluate herbage accumulation, plant-part composition and nutritive value of signal grass managed under contrasting levels of steady-state canopy heights. Treatments included 3 canopy height targets, i.e. 10 (S-short), 17.5 (M-medium) and 25 cm (T-tall), in a completely randomized design with 4 replications. Experimental units were 144-m2 plots which were grazed by groups of steers for short periods in an endeavor to keep canopy heights at the 3 desired targets. On average, herbage accumulation rate (HAR) in T pastures was greater than in M and S pastures, including the dry-wet season transition period in spring (September‒November). The S pastures had higher crude protein and lower acid detergent fiber concentrations than M and T pastures, especially in the first half of the calendar year. However, in vitro organic matter digestibility was similar for all treatments (612 g/kg). As S and M pastures had lower HARs than T pastures in the spring, it appears advantageous to maintain the signal grass canopy at ~25 cm in order to ensure quick regrowth with the return of the wet season. However, longer-term studies are needed with recording of animal performance before these initial findings can be promoted widely.

Building Envelope Thermal Mass and Its Effect on Spring and the Autumn Seasonal Transition Period

Abstract Increases in fossil fuel usage and energy consumption have become important issues in most countries of the world. Recent statistics show that the building sector is the main contributor t...

Quantifying the shifts and intensification in the annual cycles of diurnal temperature extremes for human comfort and crop production

Any significant change in climate is known to have a significant impact on crop production and human resources, which are generally difficult to quantify. In the present study, two indices are defined: (i) refined growing season (GS) characteristics and (ii) transition period, based on the annual cycles of diurnal temperature extremes, to unravel any possible impact on these productive elements. Multi-dimensional ensemble empirical mode decomposition, a nonlinear, non-stationary approach is used to extract the annual cycles of diurnal temperature extremes. Since the adverse impact is reportedly more critical over tropical regions, the Indian region is chosen as the study area, and 1° × 1° gridded daily minimum and daily maximum temperature data are used. Results reveal earlier onset and lengthening of GS, with notable spatial variations. Further, a drastic reduction in the transition (i.e. comfortable) period is observed over the warm humid regions, majorly due to the encroachment of summer days. On the contrary, over semi-arid regions, the transition period is found to be increasing, majorly due to the shortening of winter. The quantification of these changes may aid in implementing regional adaptation strategies related to the two productive elements.

Activity patterns of insectivorous bats during a seasonal transition period from hibernation to reproduction

Bat activity is influenced by fluctuating environmental variables. It may also be influenced by energetic pressures related to pregnancy, lactation, and emergence following winter inactivity. We evaluated nightly changes in relative bat activity at Royal National Park in response to Julian date, ambient temperature, precipitation, wind speed and moon phase on a nightly scale for six weeks during spring, as insectivorous bats move out of hibernation or frequent, prolonged torpor, and into the maternal season. Interestingly, later Julian date (reflecting seasonal transition) was the sole variable that best predicted total nightly activity. In addition, we opportunistically assessed bat activity in response to a severe storm, considered a Category 1 cyclone, resulting in 96.4mm of rain in one night and wind speeds up to 94km h–1. Only one species of bat, Chalinolobus gouldii, was active during the storm, with activity restricted to the latter part of the evening when precipitation had reduced, indicating rapid resumption of activity following severe weather. The results of this research can be used as an indicator of emergence from winter inactivity and highlight activity patterns of bat species in relation to environmental variables to inform timing of monitoring programs, bat surveys, and targeted research.

On the role of aerosols, humidity, and vertical wind shear in the transition of shallow-to-deep convection at the Green Ocean Amazon 2014/5 site

Abstract. The preconditioning of the atmosphere for a shallow-to-deep convective transition during the dry-to-wet season transition period (August–November) is investigated using Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) GoAmazon2014/5 campaign data from March 2014 to November 2015 in Manacapuru, Brazil. In comparison to conditions observed prior to shallow convection, anomalously high humidity in the free troposphere and boundary layer is observed prior to a shallow-to-deep convection transition. An entraining plume model, which captures this leading dependence on lower tropospheric moisture, is employed to study indirect thermodynamic effects associated with vertical wind shear (VWS) and cloud condensation nuclei (CCN) concentration on preconvective conditions. The shallow-to-deep convective transition primarily depends on humidity, especially that from the free troposphere, which tends to increase plume buoyancy. Conditions preceding deep convection are associated with high relative humidity, and low-to-moderate CCN concentration (less than the 67th percentile, 1274 cm−3). VWS, however, shows little relation to moisture and plume buoyancy. Buoyancy estimates suggest that the latent heat release due to freezing is important to deep convective growth under all conditions analyzed, consistent with potential pathways for aerosol effects, even in the presence of a strong entrainment. Shallow-only convective growth, however, shows an association with a strong (weak) low (deep) level VWS and with higher CCN concentration.

Influence of water management and natural variability on dissolved inorganic carbon dynamics in a mangrove-dominated estuary

High-resolution time series measurements of temperature, salinity, pH and pCO2 were made during the period October 2014–September 2015 at the midpoint of Shark River, a 15km tidal river that originates in the freshwater Everglades of south Florida (USA) and discharges into the Gulf of Mexico. Dissolved inorganic carbon dynamics in this system vary over time, and during this study could be classified into three distinct regimes corresponding to October 2014–February 2015 (a wet to dry season transition period), March–May 2015 (dry period) and July–September 2015 (wet period). Average net longitudinal dissolved inorganic carbon (DIC) fluxes and air-water CO2 fluxes from the Shark River estuary were determined for the three periods. Net DIC fluxes to the coast were estimated to vary between 23.2 and 25.4×105mold−1 with an average daily DIC flux of 24.3×105mold−1 during the year of study. CO2 emissions ranged between 5.5 and 7.8×105mold−1 with an average daily value of 6.4×105mold−1 during the year. The differences in estuarine carbon fluxes during the study period are attributed to differences in the relative importance of hydro-climatological drivers. Results suggest that, during months characterized by reduced rainfall, carbon fluxes are affected by water management via control structures in the upstream Everglades marshes. During months with high rainfall, when culverts are closed and rainfall events are more frequent, carbon fluxes depend more on other forcings, such as rainfall and groundwater discharge.

Single and combined phase change materials: Their effect on seasonal transition period

Phase change materials (PCMs) are being used as thermal mass in buildings to conserve energy. In this research, the application of appropriate PCMs to reduce building energy consumption and operating time of mechanical equipment during spring and autumn transition period in hot arid climate is studied. The study was conducted in buildings with diurnal occupation pattern. The simulation results were compared against measurements obtained from a calorimeter that was constructed for this purpose. The results show that PCM 29 °C and 5 air change natural ventilation rate reduce annual energy consumption by 15%. This means that while for 38 days in spring and 29 days in autumn, the mechanical equipment can be turned off. The thermal performance of PCM 25 °C is very well in spring. The appropriate PCM is the one with combined phase change melting point of 29 °C and 21 °C PCMs, which reduces energy consumption and increases the seasonal transition period 8% more than that of the single PCM 29 °C.

A New Scheme for Considering Soil Water‐Heat Transport Coupling Based on Community Land Model: Model Description and Preliminary Validation

AbstractLand surface models (LSMs) have developed significantly over the past few decades, with the result that most LSMs can generally reproduce the characteristics of the land surface. However, LSMs fail to reproduce some details of soil water and heat transport during seasonal transition periods because they neglect the effects of interactions between water movement and heat transfer in the soil. Such effects are critical for a complete understanding of water‐heat transport within a soil thermohydraulic regime. In this study, a fully coupled water‐heat transport scheme (FCS) is incorporated into the Community Land Model (version 4.5) to replaces its original isothermal scheme, which is more complete in theory. Observational data from five sites are used to validate the performance of the FCS. The simulation results at both single‐point and global scale show that the FCS improved the simulation of soil moisture and temperature. FCS better reproduced the characteristics of drier and colder surface layers in arid regions by considering the diffusion of soil water vapor, which is a nonnegligible process in soil, especially for soil surface layers, while its effects in cold regions are generally inverse. It also accounted for the sensible heat fluxes caused by liquid water flow, which can contribute to heat transfer in both surface and deep layers. The FCS affects the estimation of surface sensible heat (SH) and latent heat (LH) and provides the details of soil heat and water transportation, which benefits to understand the inner physical process of soil water‐heat migration.

An Abrupt Change in Tropospheric Temperature Gradient and Moisture Transport Over East Asia in the Late 1990s

ABSTRACTPrevious studies have shown that the recent summer climate (precipitation in particular) over East Asia is varying significantly. Here we extend the study to April, May, and June (AMJ) or the seasonal transition period associated with the onset of the summer monsoon. It is found that the average 1000–400 hPa AMJ tropospheric temperature (TT) experienced a sudden change at the end of the twentieth century. The change has a dipolar modal structure, with one pole over countries in Central Asia (Pakistan, Afghanistan, Uzbekistan, Kazakhstan, Kyrgyzstan, and Tajikistan.) and the other over the Tibetan Plateau. The difference in the TT between the centres of the two poles (∇TT), which characterizes the zonal gradient of the TT over Asia, has seen a significant reduction since 1999. The causal relations of ∇TT with the local circulation, outgoing longwave radiation (OLR), surface shortwave flux (SSWF), precipitation, etc. have been investigated using a newly developed rigorous causality analysis, which unambiguously reveals a one-way causality from ∇TT to each of OLR, SSWF, and precipitation.