Tropospheric Temperature Research Articles

Tropospheric thermal field variability over Poland in the context of climate change

AbstractBased on the results of radiosounding measurements from all Polish aerological stations, an analysis of temperature changes in the troposphere and tropopause over Poland was carried out. The study was performed for data from 1981 to 2018 at 00 UTC for five main isobaric surfaces (MISs): 850, 700, 500, 300 and 200 hPa and for the tropopause. It was found that the tropospheric temperature variability is highest in the cold months of the year and lowest in summer. Annual temperature variability in the upper troposphere is less than in the lower. Temperature trends for the MISs from 850 to 300 hPa for the year and summer are positive and almost everywhere statistically significant at a significance level of .05. For a year, they average from about 0.2°C to 0.5°C/decade. In summer, they are slightly greater and are 0.4–0.5°C. On the MIS of 200 hPa over Poland, however, there are negative thermal trends, both in the year and in summer. They are approximately −0.1°C/decade. In winter, the trends are much smaller than in the summer or for the year. In the lower troposphere they are weak and positive, while in the upper troposphere they are weak and negative. Negative tendencies in the thermal tropopause over Poland were found. For the year and seasons, this trend ranges from −0.2 to −0.3°C/decade. The obtained results regarding the temperature of the troposphere and tropopause over Poland correspond with the results of earlier studies from Europe and the around world. They confirm the warming of the lower and cooling of the upper troposphere with the tropopause, which has been taking place in the last few decades.

Environmental Controls on Tropical Mesoscale Convective System Precipitation Intensity

AbstractUsing multiple independent satellite and reanalysis datasets, we compare relationships between mesoscale convective system (MCS) precipitation intensity Pmax, environmental moisture, large-scale vertical velocity, and system radius among tropical continental and oceanic regions. A sharp, nonlinear relationship between column water vapor and Pmax emerges, consistent with nonlinear increases in estimated plume buoyancy. MCS Pmax increases sharply with increasing boundary layer and lower free tropospheric (LFT) moisture, with the highest Pmax values originating from MCSs in environments exhibiting a peak in LFT moisture near 750 hPa. MCS Pmax exhibits strikingly similar behavior as a function of water vapor among tropical land and ocean regions. Yet, while the moisture–Pmax relationship depends strongly on mean tropospheric temperature, it does not depend on sea surface temperature over ocean or surface air temperature over land. Other Pmax-dependent factors include system radius, the number of convective cores, and the large-scale vertical velocity. Larger systems typically contain wider convective cores and higher Pmax, consistent with increased protection from dilution due to dry air entrainment and reduced reevaporation of precipitation. In addition, stronger large-scale ascent generally supports greater precipitation production. Last, temporal lead–lag analysis suggests that anomalous moisture in the lower–middle troposphere favors convective organization over most regions. Overall, these statistics provide a physical basis for understanding environmental factors controlling heavy precipitation events in the tropics, providing metrics for model diagnosis and guiding physical intuition regarding expected changes to precipitation extremes with anthropogenic warming.

Boreal Spring El Niño Convective State and Its Impact on Monsoon Onset

AbstractA lesser known relationship between boreal spring El Niño state and the Indian summer monsoon (ISM) is explored, considering the differences in the evolution of sea surface temperature and convection over the Pacific. Rossby wave tracing analysis reveals that the boreal spring El Niño convective state permits two distinct eastward waveguides from the central Pacific to the ISM domain. The first waveguide reaches the northern Indian region roughly along the African‐Asian jet, and the second waveguide crosses over to the Southern Hemisphere over the eastern Pacific and extends up to the south Indian Ocean region. The net result is an altered free tropospheric temperature distribution over the ISM domain in the month of May leading to a delayed monsoon onset. The existence of the two waveguides and the modulation of monsoon onset makes the boreal spring El Niño state an important component to be accounted for in ISM prediction.

Multi-Frequency Analysis of Simulated versus Observed Variability in Tropospheric Temperature

AbstractStudies seeking to identify a human-caused global warming signal generally rely on climate model estimates of the “noise” of intrinsic natural variability. Assessing the reliability of these noise estimates is of critical importance. We evaluate here the statistical significance of differences between climate model and observational natural variability spectra for global-mean mid- to upper-tropospheric temperature (TMT). We use TMT information from satellites and large multimodel ensembles of forced and unforced simulations. Our main goal is to explore the sensitivity of model-versus-data spectral comparisons to a wide range of subjective decisions. These include the choice of satellite and climate model TMT datasets, the method for separating signal and noise, the frequency range considered, and the statistical model used to represent observed natural variability. Of particular interest is the amplitude of the interdecadal noise against which an anthropogenic tropospheric warming signal must be detected. We find that on time scales of 5–20 years, observed TMT variability is (on average) overestimated by the last two generations of climate models participating in the Coupled Model Intercomparison Project. This result is relatively insensitive to different plausible analyst choices, enhancing confidence in previous claims of detectable anthropogenic warming of the troposphere and indicating that these claims may be conservative. A further key finding is that two commonly used statistical models of short-term and long-term memory have deficiencies in their ability to capture the complex shape of observed TMT spectra.

Characteristics of the upper troposphere wind field according to the satellite measurements and their connection with climatic parameters

The results of the study of the spatio-temporal variability of the main characteristics of jet streams and turbulence zones in the upper troposphere of the Northern Hemisphere according to measurements from European geostationary meteorological satellites for the period 2007 - 2018 are presented. Their relationship with the essential parameters of the Earth’s climate system — the temperature of the troposphere, the area of sea ice, and also large-scale atmospheric phenomena is considered. It has been shown that over the past 12 years there has been a significant increase in the area of regions occupied by relatively weak and moderate turbulence and a slight decrease in areas with strong and very strong turbulence. Based on the cross-wavelet analysis in the time-frequency space, the relationships between the variations in the areas of the turbulent regions and the majority of the characteristics of jet streams are revealed. A close relationship has been established between the characteristics of jet streams and the areas of turbulent zones with the temperature of the upper troposphere. In this case, the effect of temperature on the area of turbulent zones manifests itself indirectly through the characteristics of jet streams. A significant association of variations in the average area of the jet stream and the latitudinal position of its center with the area of sea ice are noted. According to spectral and wavelet analysis of the characteristics of jet streams, along with annual and quasi-biennial oscillations, short-period oscillations are observed with periods in the range of 10-40 days, which can be interpreted as a manifestation of Rossby waves..

Arctic Ozone Loss in March 2020 and its Seasonal Prediction in CFSv2: A Comparative Study With the 1997 and 2011 Cases

AbstractUsing reanalysis data, observations, and seasonal forecasts, the March Arctic ozone loss events in 1997, 2011, and 2020 and their predictability are compared. All of the three ozone loss events were accompanied by an extremely strong and cold polar vortex, with the shape and centroid of the ozone loss controlled by the polar vortex. The high autocorrelation of the March Arctic ozone at a lead/lag time of 1–2 months from observations might suggest that a reasonable prediction can be obtained if one initializes 1–2 months in advance. Based on the chemical scheme assessment in CFSv2 and several empirical models using the forecasted metric(s) of the stratospheric polar vortex as predictor(s), the predictability of the 2011 ozone loss event is shown to be longer (1–2 months) than the other two (~1 month), possibly due to a moderate La Niña and quasi‐biennial oscillation westerly winds favorable for the formation of a strong polar vortex. However, the overall predictive skills of ozone from empirical models (using a forecasted substitute index to forecast the Arctic ozone) during 1982–2020 are lower than the chemical module assessment in the forecast system, though empirical models have some skill. Contrary to the ozone predictions, the lower tropospheric temperature pattern in March 2011 is less reasonable than in 1997 and 2020. Similar conclusions are also true in other years (2005 versus 2016). Those findings might indicate a weak relationship between the Arctic ozone and the surface climate in the Northern Hemisphere.

Influence of convection on stratospheric water vapor in the North American monsoon region

Abstract. We quantify the connection between deep convective occurrence and summertime 100 hPa water vapor anomaly over the North American (NA) region and find substantial consistency between their interannual variations and also that the water vapor mixing ratio over the NA region is up to ∼1 ppmv higher when deep convection occurs. We use a Lagrangian trajectory model to demonstrate that the structure and the location of the NA anticyclone, as well as the tropical upper tropospheric temperature, mediate the moistening impact of convection. The deep convection mainly occurs over the Central Plains region. Most of the convectively moistened air is then transported to the center of the NA anticyclone, and the anticyclonic structure helps maintain high water vapor content there. This explains both the summer seasonal cycle and interannual variability of the convective moistening efficiency in the NA region and can provide valuable insight into modeling stratospheric water vapor.

A simulation comparison of calibration functions for different sets of spectral filter passbands in the traditional pure rotational Raman lidar technique

The accuracy of tropospheric temperature measurements with pure rotational Raman (PRR) lidars is affected by the collisional broadening of N2 and O2 PRR lines. In this paper, we intercompare nine calibration functions (CFs) in the traditional PRR lidar technique via simulation. Taking into account the PRR line broadening, the simulation is performed for five sets of spectral filters (SFs) with different passbands in a PRR lidar receiving system. For simplicity of calculations, the transmission function of each SF is approximated by a rectangular function on the wavenumber interval, within which a SF passes the bulk of the backscattered signal intensity in the corresponding PRR lidar channel. A narrow-linewidth laser operating at wavelengths of 354.67 and 532 nm is considered as a lidar transmitter. The CF best suited for tropospheric temperature retrievals from raw PRR lidar data for each set of SFs and laser wavelength is determined by comparative analysis of calibration errors ΔT produced using these CFs. The absolute error |ΔT| does not exceed the value of 3 × 10–3 K when using the best three-coefficient CF, while |ΔT| < 4 × 10–4 K for the best four-coefficient CF regardless of the laser wavelength and SF set used.

Context of the added value in coupled atmosphere-land RegCM4–CLM4.5 in the simulation of Indian summer monsoon

The potential of the RegCM4–CLM4.5 model for value addition over the MIROC5 GCM for Indian Summer Monsson (ISM) simulation for the present climate (1975–2005) has been examined. The added value has been investigated in terms of the added value index (AV) and the Modified Brier Skill Score (MBSS). In general, a strong dry (wet) bias > 5 mm/day in the RegCM4 (MIROC5) dataset was prevalent over different parts of India. Additional precipitation statistics such as the area-averaged mean, standard deviation, correlation coefficient, and percentage bias over the homogeneous region of precipitation suggest that the RegCM4 occasionally improves over the MIROC5, depending upon the region and the metric under consideration. Further, a comparable tropospheric temperature gradient and the vertical wind shear have been found for both the dataset. However, this does not hold for the large-scale moisture transport as the RegCM4 shows an advantage in representing the magnitude and the location of the low-level jet. The dominant unrealistic moisture transport and associated stronger Bay of Bengal branch of circulation causes heavy precipitation (> 12 mm/day), thus leading to improved precipitation statistics for MIROC5. A quantifiable added value over the GCM in terms of the positive indices have been found in the RegCM4. The AV (MBSS) suggests positive values i.e. 0.6–0.8 (0.2–0.5) over major parts of India, signifying added information and/or the improvement upon the downscaling. The experiment certainly provides additional information in the precipitation simulation over the major part of India however the two indices do not necessarily agree over certain areas.

Infrared Fourier Spectrometer 2 (IKFS‐2) radiance assimilation at ECMWF

AbstractMeteorological satellites launched as part of the Russian space programme have not been widely used in global numerical weather prediction (NWP) to date. There is particular interest in the Meteor‐M series of sun‐synchronous spacecraft, as it is anticipated that future launches will operate in currently unobserved orbital planes complementary to those occupied by Europe, the United States, and China. One of the sensors carried on board these satellites is the Infrared Fourier Spectrometer 2 (IKFS‐2), which observes a spectrum of atmospheric radiation over the wavenumber range 660–2,000.5 cm−1. The IKFS‐2 is thus similar to earlier hyperspectral sensors such as the Infrared Atmospheric Sounding Interferometer (IASI) and the Cross‐track Infrared Sounder (CrIS), both of which have been used operationally at the European Centre for Medium‐range Weather Forecasts (ECMWF) for many years. This study investigates the quality of IKFS‐2 radiance measurements from the Meteor‐M‐N2 satellite and performs assimilation experiments to assess the impact of these data on the ECMWF analysis and forecasting system. Measured by statistical indicators of the observation fit to short‐range forecasts, the IKFS‐2 performs as well as IASI and CrIS amongst channels sensitive to stratospheric and tropospheric temperature. The assimilation experiments indicate up to 0.5% improvement in headline forecast scores, although the medium‐range impact is mixed and for most parts nonsignificant. One factor that currently limits the impact of IKFS‐2 is poor data timeliness and availability: observations are available for assimilation typically only 75% of the time during the test periods. It is expected, though, that such logistical problems can be overcome, and efforts are already underway to improve data dissemination.

Solar cycle modulation of the connection between boreal winter ENSO and following summer South Asia high

In this study, the solar cycle modulation of the connection between boreal winter El Niño-South Oscillation (ENSO) and following summer South Asia High (SAH) are revealed. For El Niño accompanied by low solar cycle (EL & LS) or La Niña accompanied by low solar cycle (LA & LS), the boreal winter ENSO prominently affects the following summer's SAH variation. The SAH is enhanced (weakened) and expanded (narrowed) in the meridional and zonal directions in the EL & LS (LA & LS) phase. The composite difference in the SAH between El Niño and La Niña events is obviously stronger in the low solar cycle phase. In low solar cycle phase, El Niño signal and charging process are stronger, which lead to stronger warming sea surface temperature (SST) appear in tropical Indian Ocean and Maritime Continent extending to northwestern Pacific, resulting in larger SAH variations via warming tropospheric temperature. However, for El Niño with a high solar cycle (EL & HS) or La Niña with a high solar cycle (LA & HS), the variations in the SAH and the composite difference of the SAH between El Niño and La Niña events are quite weak in the high solar cycle phase. The charging process over tropical Indian Ocean induced by El Niño is weaker in the high solar cycle phase, which leads to weaker warming SST appear over tropical Indian Ocean, resulting in smaller SAH variations.Further investigation based on longer historic data also ensures that the 11-year solar cycle modulates the ENSO-SAH connection, with a more robust connection in the low solar cycle phase. The 11-year solar cycle should be considered when investigating the connection between the preceding winter ENSO and following summer SAH variations.

The vertical profile of recent tropical temperature trends: Persistent model biases in the context of internal variability

Tropospheric and stratospheric tropical temperature trends in recent decades have been notoriously hard to simulate using climate models, particularly in the upper troposphere. Aside from the warming trend itself, this has broader implications, e.g. atmospheric circulation trends depend on latitudinal temperature gradients. In this study, tropical temperature trends in the CMIP6 models are examined, from 1979 to 2014, and contrasted with trends from the RICH/RAOBCORE radiosondes, and the ERA5/5.1 reanalysis. As in earlier studies, we find considerable warming biases in the CMIP6 modeled trends, and we show that these biases are linked to biases in surface temperature. We also uncover previously undocumented biases in the lower-middle stratosphere: the CMIP6 models appear unable to capture the time evolution of stratospheric cooling, which is non-monotonic owing to the Montreal Protocol. Finally, using models with large ensembles, we show that their standard deviation in tropospheric temperature trends, which is due to internal variability alone, explains ∼ 50% (± 20%) of that from the CMIP6 models.

Methane Emissions in a Chemistry-Climate Model: Feedbacks and Climate Response.

Understanding the past, present, and future evolution of methane remains a grand challenge. Here we have used a hierarchy of models, ranging from simple box models to a chemistry‐climate model (CCM), UM‐UKCA, to assess the contemporary and possible future atmospheric methane burden. We assess two emission data sets for the year 2000 deployed in UM‐UKCA against key observational constraints. We explore the impact of the treatment of model boundary conditions for methane and show that, depending on other factors, such as CO emissions, satisfactory agreement may be obtained with either of the CH4 emission data sets, highlighting the difficulty in unambiguous choice of model emissions in a coupled chemistry model with strong feedbacks. The feedbacks in the CH4‐CO‐OH system, and their uncertainties, play a critical role in the projection of possible futures. In a future driven by large increases in greenhouse gas forcing, increases in tropospheric temperature drive, an increase in water vapor, and, hence, [OH]. In the absence of methane emission changes this leads to a significant decrease in methane compared to the year 2000. However, adding a projected increase in methane emissions from the RCP8.5 scenario leads to a large increase in methane abundance. This is modified by changes to CO and NOx emissions. Clearly, future levels of methane are uncertain and depend critically on climate change and on the future emission pathways of methane and ozone precursors. We highlight that further work is needed to understand the coupled CH4‐CO‐OH system in order to understand better future methane evolution.

The Climatology of Lower Tropospheric Temperature Inversions in China from Radiosonde Measurements: Roles of Black Carbon, Local Meteorology, and Large-Scale Subsidence

AbstractThe variability of the lower tropospheric temperature inversion (TI) across China remains poorly understood. Using seven years’ worth of high-resolution radiosonde measurements at 120 sites, we compile the climatology of lower tropospheric TI in terms of frequency, intensity, and depth during the period from 2011 to 2017. The TI generally exhibits strong seasonal and geographic dependencies. Particularly, the TI frequency is found to be high in winter and low in summer, likely due to the strong aerosol radiative effect in winter. The frequency of the surface-based inversion (SBI) exhibits a “west low, east high” pattern at 0800 Beijing time (BJT), which then switches to “west high, east low” at 2000 BJT. Both the summertime SBI and elevated inversion (EI) reach a peak at 0800 BJT and a trough at 1400 BJT. Interestingly, the maximum wintertime EI frequency occurs over Southeast China (SEC) rather than over the North China Plain (NCP), likely attributable to the combination of the heating effect of black carbon (BC) originating from the NCP, along with the strong subsidence and trade inversion in SEC. Correlation analyses between local meteorology and TI indicate that larger lower tropospheric stability (LTS) favors more frequent and stronger TIs, whereas the stronger EI under smaller LTS conditions (unstable atmosphere) is more associated with subsidence rather than BC. Overall, the spatial pattern of the lower tropospheric TI and its variability in China are mainly controlled by three factors: local meteorology, large-scale subsidence, and BC-induced heating. These findings help shed some light on the magnitude, spatial distribution, and underlying mechanisms of the lower tropospheric TI variation in China.

Characterizing Temperature and Aerosol Variability During Jupiter's 2006–2007 Equatorial Zone Disturbance

AbstractWe use ground‐based mid‐infrared (8–20 μm) data acquired by three different instruments between 2005 and 2008 to characterize the variability of tropospheric temperature and aerosol opacity during the 2006–2007 Equatorial Zone disturbance. This disturbance is part of a repeating pattern of cloud‐clearing events at Jupiter's equator, observed as a significant brightening at 5 μm (sensing the 2‐ to 7‐bar region) and darkening at visible wavelengths (sensing the ∼0.7‐bar pressure level). The data reveal a brightness temperature increase of ∼3.1 K between 2005 and February 2007 at 8.6‐μm sensing tropospheric aerosol opacity and temperature near 0.6–0.8 bar. At wavelengths sensing tropospheric ammonia and temperatures between 150 and 600 mbar, the brightness temperature remains largely invariant between 2005 and 2008. The tropospheric vertical temperature profile and the tropospheric aerosol opacity were derived from images captured in different filters on four different dates, one for each year. The retrieved aerosol opacity at ∼0.6–0.8 bar shows a decrease at 2–5°S of ∼45% in 2006 and ∼65% in 2007, with respect to 2008. This is consistent with cloud clearing/thinning during the coloration of the Equatorial Zone at visible wavelengths. This brightening at 8.6 μm started in 2005 and preceded the brightening at 5 μm, which started in April 2006. The results also suggest that cloud clearing during the Equatorial Zone disturbances is not simply the result of tropospheric warming, at least at p &lt; 0.7 bar. We propose that cloud clearing occurs due to a decrease in the ammonia gas upwelling at the equator.

Genesis potential parameter using satellite derived daily tropical cyclone heat potential for North Indian ocean

ABSTRACT Tropical Cyclone Heat Potential (TCHP) is the heat content relative to 26°C isotherm, which is important in the development of cyclone. Cyclonic events last for few weeks and become intensified within few days or in some cases few hours. To study such low pressure systems, daily TCHP is required which is created in our study using Two Layer Gravity Model (TLGM) using monthly climatologies of temperature and salinity profiles, daily Sea Surface Height Anomaly (SSHA) and daily Sea Surface Temperature (SST). This satellite-based data of SSHA and SST are used to create daily TCHP fields which are validated using collocated ARGO in-situ data. ARGO derived TCHP and TLGM TCHP showed correlation coefficient , which indicates that TLGM can be used for near real time TCHP calculation for cyclone studies. Analysis done on 92 non-developing and 93 developing systems shows that, on the day of formation of depression, average TCHP is 89.3 kJ cm for developing systems while average TCHP is 78.3 kJ cm for non-developing systems in North Indian Ocean (NIO). Minimum TCHP was found to be 27.2 kJ cm and 28.6 kJ cm for developing and non developing systems out of 93 and 92 cases, respectively. Further, Genesis Potential Parameter (GPP) using low-level relative vorticity, middle troposphere relative humidity, middle troposphere temperature instability and vertical wind shear is created based on past similar studies, but with six hourly as well as daily resolution (1993 to 2017) and 0.125° 0.125° spatial resolution. Using daily TCHP, another index called Genesis Potential Index (GPI) is created and then both the GPP and GPI are analysed for 93 developing and 92 non-developing systems in north Indian ocean from the year 1993 to 2017. Our study shows that both are good predictors for the lead periods of less than 2 days, while for the lead periods of more than 2 days, the distinction becomes difficult between developing and non-developing systems. Abbreviations: TLGM - Two Layer Gravity Model; TCHP - Tropical Cyclone Heat Potential; - Depth of 26°C isotherm; - Depth of 20°C isotherm; NIO - North Indian Ocean; AS - Arabian Sea; India Meteorological Department - IMD; BOB - Bay of Bengal

Southward Shift of Westerlies Intensifies the East Asian Early Summer Rainband Following El Niño

AbstractAn intensification of East Asian rainfall usually occurs in summers following El Niño. We propose that this teleconnection is mediated via the westerlies impinging on the Tibetan Plateau, through El Niño's control on tropical tropospheric temperature. This is distinct from previous studies that attribute the El Niño's influence to changes in the western Pacific subtropical anticyclone. The warming in the eastern equatorial Pacific leads to uniform warming of the entire tropical troposphere, which sharpens the temperature gradient between the tropics and the subtropics and shifts the westerlies southward. The westerlies impinge over the Tibetan Plateau for longer and, through interaction with the topography, induce intense and persistent extratropical northerlies downstream of the plateau that in turn intensifies the East Asian rainband. The rainband has previously been shown to intensify in a similar manner in a warming climate, suggesting that the El Niño response provides an analog for future changes.

Modeling seasonal trends in optimum temperatures over India

AbstractGlobal warming and changes in seasonal temperature can severely affect the general circulation and precipitation distribution of a region. Therefore, it becomes essential to analyze seasonal trends in air temperature with changing climate. The present study evaluates the troposphere temperature extremes over India during different seasons. We intend to identify significant trends in temperature distribution in different regions of India using the Mann–Kendall test. Further, we have calculated indices concerning temperature extremes to make inferences about the nature of this monotonicity at four pressure levels on a seasonal and annual basis. The temperature data being used in our analysis is obtained from the output of a Regional Climate Model version 4.6 (RegCM v4.6). The monthly temperature values are taken for 25 years (1982–2006) from the model output. We observed that the model captured temperature climatology is coherent with our theoretical analysis. Results of our study reveal a significant (p &amp;lt; 0.05) trend in TT during all the seasons in major parts of the country in the lower troposphere. The upper troposphere, on the other hand, does not show any significant trend during most of the seasons. The identification of these changes can be useful for analysis of coastal vulnerability and extreme weather conditions.

Links between the thermal condition of the Tibetan Plateau in summer and atmospheric circulation and climate anomalies over the Eurasian continent

We examine the links between the thermal condition of the troposphere over the Tibetan Plateau with the atmospheric circulation and climate over the Eurasian continent. The temperature of the troposphere over the Tibetan Plateau is higher than the temperature in other regions at the same latitude and is consistent with the temperature of the Eurasian troposphere on an interannual timescale. The higher temperature of the troposphere over the Tibetan Plateau leads to anomalous south–north temperature gradients from mid-latitudes over the Eurasian continent to its two flanks, accompanied by anomalous easterly and westerly winds in the upper troposphere in the subtropics and at higher latitudes. Anomalous anticyclonic circulations and subsidence motions appear between the anomalous easterly and westerly winds and contribute to the high surface air temperature over West Asia, Central Asia and East Asia via anomalous vertical temperature advection in the troposphere and change in the amount of solar radiation incident on the surface. The enhanced East Asian summer monsoon associated with the high temperature of the troposphere over the Tibetan Plateau also partly contributes to the high surface air temperature over East Asia via horizontal temperature advection. The westerly wind anomalies in the north of the mid-latitudes over the Eurasian continent indicate the enhancement and northward shift of the mid-latitude westerly jet. This is related to anomalous upward motion and higher precipitation in Northeast China and North China. Sensitivity experiments based on an atmospheric model verify the impact of anomalous tropospheric heating over the Tibetan Plateau in summer on the atmospheric circulation over the Eurasian continent.

The Long-Term Trend of Upper-Air Temperature in China Derived from Microwave Sounding Data and Its Comparison with Radiosonde Observations

AbstractCurrently, the satellite Microwave Sounding Unit (MSU/AMSU) datasets developed from three organizations—Remote Sensing Systems (RSS), the University of Alabama at Huntsville (UAH), and the NOAA Center for Satellite Applications and Research (STAR)—are often used to monitor the global long-term trends of temperatures in the lower troposphere (TLT), midtroposphere (TMT), total troposphere (TTT), troposphere and stratosphere (TTS), and lower stratosphere (TLS). However, the trend in these temperatures over China has not been quantitatively assessed. In this study, the decadal variability and long-term trend of upper-air temperature during 1979–2018 from three MSU datasets are first evaluated over China and compared with the proxy MSU dataset simulated from homogenized surface and radiosonde profiles (EQU) at 113 stations in China. The regional mean MSU trends over China during 1979–2018 are 0.22–0.27 (TLT), 0.15–0.22 (TMT), 0.20–0.27 (TTT), 0.02–0.14 (TTS), and from −0.33 to −0.36 (TLS) K decade−1, whereas the EQU trends are 0.31 (TLT), 0.19 (TMT), 0.24 (TTT), 0.07 (TTS), and −0.26 (TLS) K decade−1. The trends from RSS generally show a better agreement with those from EQU. The trends from both MSU and EQU exhibit seasonal and regional difference with a larger warming in TLT in February and March, and stronger cooling in TLS from late winter to spring. The TLT and TMT over the Tibetan Plateau and northwestern China show larger warming trends. The variability from MSU and EQU agree well except TLT in Tibet and southern China. The major difference in regional mean temperatures over China between MSU and EQU is related primarily to the satellite instrument changes during 1979–98 and the radiosonde system changes in China in the 2000s.