Mean Tropospheric Temperature Research Articles

An Asian–Pacific teleconnection in summer tropospheric temperature and associated Asian climate variability

We identified the Asian-Pacific Oscillation (APO) and its associated index, a zonal teleconnection pattern over the extratropical Asian-Pacific region. This was done through the correlation and empirical orthogonal function (EOF) analyses on the summer mean tropospheric eddy temperature from the monthly European Center for Medium-Range Weather Forecast reanalysis. The APO reflects an out-of-phase relationship in variability of the eddy temperature between Asia and the North Pacific and is associated with the out-of-phase relationship in atmospheric heating. The APO index shows a decadal variation, tending to a high-index polarity before 1975 and afterward to a low-index polarity. Moreover, the APO index has a quasi-5-year period. With higher APO-index conditions in the upper troposphere, the summer South Asian high and the North Pacific trough are stronger, while the westerly jet stream over Asia and the easterly jet stream over South Asia strengthen. Also, the Asian low and the North Pacific subtropical high are stronger in the lower troposphere. The anomalous southerlies prevail at the midlatitudes of East Asia, accompanied by a more northward Mei-yu front, and the anomalous westerlies prevail over South Asia. Summer rainfall increases in North China, South China, and South Asia, while it decreases from the valley of the Yangtze River to southern Japan, and near the Philippines.

Deriving the tropospheric integrated water vapor from tipping curve–derived opacity near 22 GHz

In this study we present a simple relation between the tropospheric opacity τ near 22.235 GHz and the integrated water vapor (IWV) content of the troposphere. The opacity is measured at Bern, Switzerland, by the radiometer Middle Atmospheric Water Vapour Radiometer (MIAWARA), designed for middle atmospheric water vapor profile measurements. In contrast to typical radiometers for tropospheric monitoring, this middle atmospheric water vapor radiometer only measures in the vicinity of the 22.235 GHz water vapor line with a bandwidth of 1 GHz. With this study we show that it is even possible to derive the integrated tropospheric water vapor (IWV) content of the atmosphere using this limited frequency range if the liquid water content of the atmosphere is negligible. IWV measurements of the tropospheric monitoring instruments Tropospheric Water Vapour Radiometer (TROWARA, two‐channel radiometer), All‐Sky Multi Wavelength Radiometer (ASMUWARA, multichannel radiometer), and GPS, which are operated next to MIAWARA, are used to derive a linear relation between the opacity and the water vapor content of the troposphere. In a second step, the mean tropospheric temperature is taken into account and a slight improvement of the linear relation is achieved. All instruments involved in this study are contributing to the Studies in Atmospheric Radiative Transfer and Water Vapour Effects (STARTWAVE) project of the Climate program of the National Competence Center in Research. The MIAWARA measurements in the subarctic winter in northern Finland during the Lapbiat Upper Tropospheric Lower Stratospheric Water Vapor Validation Project (LAUTLOS/WAVVAP) campaign in 2004 are compared to radiosonde measurements by the Finnish Meteorological Institute using the same algorithm that was derived for Bern. The agreement of MIAWARA IWV and radiosonde IWV is of the same order as for Bern. Finally, Payerne radiosonde measurements and model simulation using the Atmospheric Radiative Transfer Simulator (ARTS) software and the continuum absorption models of Rosenkranz (1998) and Liebe (MPM87/MPM93) confirm the derived opacity‐IWV relation. This study shows that the integrated water vapor content of the troposphere can be measured by a radiometer operating near the 22.235 GHz water vapor line using a bandwidth of 1 GHz, if the liquid water content of the atmosphere is negligible.

Weakening of Indian summer monsoon in recent decades

The analysis of 43 years of NCEP-NCAR reanalysis data and station observations reveals the connections between tropospheric temperature variations and the weakening of the Indian summer monsoon circulation. The Indian summer monsoon variation is strongly linked to tropospheric temperature over East Asia, showing significant positive correlations of mean tropospheric temperature with all-Indian summer rainfall and the monsoon circulation intensity. The result shows that Indian summer monsoon circulation underwent two weakening processes in recent decades. The first occurred in circa the mid-1960s, and the other occurred in circa the late 1970s. The finding indicates that the mean tropospheric temperature may play a crucial role in the weakening of the Indian summer monsoon intensity via changing land-sea thermal contrast. The role of the tropospheric temperature contrast between East Asia and the tropical area from the eastern Indian Ocean to the tropical western Pacific is to weaken the Indian summer monsoon circulation.

Interdecadal Variability of the Seasonal-scale Persistence in the Tropical Mean Tropospheric Temperature

After the climate shift of 1976/1977, associated with the interdecadal variability in the tropical Pacific Ocean, persistence barriers of El Nino/Southern Oscillation (ENSO) and tropical mean tropospheric temperature (TMTT) variations are detected in the boreal spring and autumn, respectively. Prior to the climate shift, however, the TMTT persistence barrier is almost non-existent, despite the prominence of the ENSO persistence barrier. Thus, the phase lag between ENSO and the TMTT variations is not fixed prior to the climate shift, while there is a fixed lag after the climate shift. This interdecadal variability is most remarkable for the TMTT anomalies in December. After the climate shift, the TMTT anomalies in December tend to persist 4 months later than prior to the climate shift. This is further examined in the comparison to the SST averaged over the strongly precipitating regions only, that is, the rainy-region SST. The SST variations in the rainy-region well correspond to those over the remote ocean basins, such as the Indian Ocean and the Western Pacific, that show a lagged response to the equatorial eastern Pacific SST anomalies. The TMTT anomalies are positively correlated with the rainy-region SST anomalies in both periods, prior to and after the climate shift. The interdecadal variability of the rainy-region SST persistence is similar to that of the TMTT persistence, although the variability is not as distinct as that of the TMTT.

Global warming trend of mean tropospheric temperature observed by satellites.

We have analyzed the global tropospheric temperature for 1978 to 2002 with the use of passive microwave sounding data from the NOAA series of polar orbiters and the Earth Observing System Aqua satellite. To accurately retrieve the climatic trend, we combined the satellite data with an analytic model of temperature that contains three different time scales: a linear trend and functions that define the seasonal and diurnal cycles. Our analysis shows a trend of +0.22 degrees to 0.26 degrees C per 10 years, consistent with the global warming trend derived from surface meteorological stations.

Determination of weighted mean tropospheric temperature using ground meteorological measurements

The weighted mean tropospheric temperature is a critical parameter in the conversion of wet zenith delay to precipitable water vapor in GPS Meteorology. This parameter can not be calculated from the radiosonde data in real time through the conventional methods. In this study, we first discuss the admissible error of weighted mean temperature to enable the accuracy of the conversion better than 1 mm, then summarize the performance of some of the existing methods. An empirical formula is established that satisfies the real-time requirement in GPS meteorology using Sequential Regression Analysis method. It is shown that this real-time formula as compared with other empirical methods is more accurate for local applications.

Estimated Impacts on Climate Records of Adaptive Strategies for Scheduling Radiosondes

Abstract Possible changes to the North American Atmospheric Observing System that are under discussion include the scheduling of radiosonde launches according to synoptic conditions. The authors estimate biases in long-term monthly mean tropospheric temperature and humidity resulting from reducing the number of radiosonde launches at a site depending on synoptic conditions. The sign and magnitudes of the biases vary considerably with geographic location and sometimes with season. Such biases would contaminate the upper-air climatology and complicate the calculation of climate trends. Approaches for minimizing these biases are explored.

Weighted mean tropospheric temperature and transmittance determination at millimeter‐wave frequencies for ground‐based applications

A simple model for the radiometric determination of tropospheric transmittance is based on an isothermal troposphere. In this model the key parameter is the weighted mean tropospheric temperature Tm, which characterizes the radiation and temperature properties of the troposphere. Statistical approaches in modeling this parameter are presented here by using ground temperature, ground relative humidity, and radiometer data. In order to determine the statistical coefficients for Tm modeling and the parameters used in the transmittance retrieval algorithm, radiosonde data were used in a millimeter‐wave propagation model for a site in the Swiss central plane and an Alpine site. Various observing geometries at different millimeter‐wave frequencies were considered. A determination of Tm from ground temperature was achieved with a rms error between 4–5 K for the low‐altitude site and 3–4 K for the high‐altitude site. By incorporating relative humidity or radiometer data, an improvement of up to 25% relative to these values results, depending on frequency and site. The zenith transmittance estimations for the low‐altitude site with our best model have a rms error of 0.5% at 38 GHz, 1% at 94, 110, and 142 GHz, 1.5% at 115 GHz, 2% at 204 GHz, and 3.5% at 279 GHz, whereas for the high‐altitude site all rms errors are below 1%. The inclusion of radiometric information at 20 and 31 GHz did not provide any additional improvement, which was confirmed by actual measurements at 142 GHz.

ENSO Seasonality: 1950–78 versus 1979–92

ENSO-related seasonal-to-interannual variability in the Pacific basin is documented, based on marine surface observations of monthly mean sea surface temperature, sea level pressure, and wind, together with satellite-based estimates of rainfall and mean tropospheric temperature. Anomalies in these fields are linearly regressed onto simultaneous values of an index of equatorial Pacific SST anomalies. The analysis is performed separately on the data for earlier (1950–78) and later (1979–92) epochs of the record. The analyses are further stratified in terms of the climatological-mean warm and cold seasons in the equatorial Pacific, which correspond to January–May and July–November, respectively. Composite SST, wind, and rainfall fields for he warm and cold seasons that fall within typical warm and cold ENSO episodes are also presented. Despite the dramatic differences in the sequencing of ENSO warm episodes with respect to the annual march in the two epochs, the anomaly patterns are found to be remarkably similar and generally consistent with the Rasmusson and Carpenter composite. SST and zonal wind anomalies were quite comparable in strength in the warm and cold seasons, although the distributions were somewhat different. Rainfall anomalies and the associated anomalies in surface wind convergence and mean tropospheric temperature were much stronger during the warm season (and particularly during January–February) than during the cold season. Some aspects of the observed rainfall anomaly seasonality can be explained on the basis of simple thermodynamical considerations.

Intraseasonal Variability in Tropical Mean Temperature and Precipitation and Their Relation to the Tropical 40–50 Day Oscillation

Abstract Intraseasonal variability of tropical mean tropospheric temperature and precipitation are investigated using newly available gridded datasets from the satellite-based microwave sounding unit (MSU). Lag regression and cross-spectrum analysis reveal a strong, dynamically consistent, zonally symmetric component of the tropical 40–50 day oscillation. A fast eastward propagating signal is found in upper-tropospheric temperature and zonal wind, emanating, from the region of enhanced precipitation associated with the 40–50 day oscillation. The temperature signal is consistent with an interpretation in terms of the transient tropospheric response to the switch-on of an equatorial heat source, in the form of a Kelvin wave front, and a recently detected very fast (˜40 m s−1) tropical tropospheric signal, with a vertical structure suggestive of the first baroclinic mode. Such fast moving wave fronts are hypothesized to be instrumental in maintaining the observed high degree of homogeneity in tropical temper...

Long term variations of atmospheric synoptic variability: A study based on radiosonde data from Lindenberg (Germany)

In an extension of a study by Fraedrich et al. (1979a, b) we show how the atmospheric processes generating a local climate state can vary from year to year and between two decades in Eastern Germany - an area which is frequently visited by mature cyclones. On the basis of homogeneous and long (1971-90) time series of 4 times daily radiosonde ascents of the GDR we investigated the interannual variability of monthly means, synoptic variability (variance/covariance with periods between 2 and 8 days, weather), low frequency variability (periods of 10-30 days), and high frequency variability (periods of less than one day, noise) of geopotential, temperature, zonal and meridional wind and specific humidity at 14 levels between 925 and 50 hPa. For the time interval 1971-90 we find that the already described significant increase of monthly mean tropospheric temperature and mean zonal wind is accompanied both by changes of different transports carried out by the time mean circulation and by significant changes of monthly variances and transports by eddies of different scales. Additionally we suggest for further studies of interannual variability of atmospheric processes based on radiosonde data applying a low pass filter on the data removing fluctuations with a period of less than one day before making any further operation with the data

On the Evolution of theQE IIStorm. II: Dynamic and Thermodynamic Structure

Abstract The existence of convection and the hurricane-like structure in the explosively-developing cyclone studied in Part I motivates us to assess the importance heating had on this cyclogenesis. To accomplish this, a method to evaluate the three-dimensional thermodynamic and dynamic structure of the atmosphere is proposed, so that we may evaluate potential vorticity changes in the vicinity of this cyclone. Results indicate a 24 h lower tropospheric generation of from five to thirteen times the value observed at 1200 GMT 9 September 1978. An evaluation of physical effects on thickness change following the surface center shows a large mean tropospheric temperature rise to be due to bulk cumulus heating effects, which could be important in the extraordinary potential vorticity generation concurrent with this cyclone's explosive development. These vertically integrated values of heating motivate us to solve the quasi-geostrophic omega and vorticity equations forced by an idealized heating function with spe...

Variation in Size and Location of the 300 mb North Circumpolar Vortex Between 1963 and 1975

Abstract The time variation in size and location of the 300 mb north circumpolar vortex has been estimated from mean monthly polar stereographic maps for the years 1963–75, both by planimetering the area north of height contours in the main belt of westerlies and by determining the colatitude of these contours at 30° longitude intervals and squaring the average value. It is shown that the vortex areas determined by the two independent techniques are in excellent agreement, but that the vortex-center locations (based on equalization of arms) determined by the two techniques are in only fair agreement. The change in vortex area appears mainly to reflect a change in mean tropospheric temperature, but with some modification caused by a change in mean surface pressure in temperate latitudes. Since 1970 the yearly averaged vortex area has increased by almost 2%, but that increase apparently ended in 1975, suggesting that the cooling in north temperate latitudes has also ended. During this same five-year period ...