Lapse rate deviations from the moist adiabat in the tropical upper troposphere in climate models

2020 ◽  
Author(s):  
Paul Keil ◽  
Hauke Schmidt ◽  
Bjorn Stevens
Keyword(s):  
Climate Models ◽  
Lower Troposphere ◽  
Lapse Rate ◽  
Cmip5 Models ◽  
Upper Troposphere ◽  
Microphysical Parameters ◽  
The Mean ◽  
Lapse Rates ◽  
The Tropics ◽  
Mean State

<p>The tropospheric lapse rate in the tropics follows a moist adiabat quite closely and is mainly set by surface temperature and humidity in the convecting regions. Therefore, warming or biases at the surface are transferred via the moist adiabat to the upper troposphere. However, climate models show large discrepancies in the upper troposphere and recent observed upper tropospheric warming is around 0.5K weaker than predicted by the moist adiabat theory. Here we use the control simulations of the CMIP5 ensemble to show that large differences in the upper troposphere exist in the mean state that are unrelated to inter-model differences in the lower troposphere. In fact, CMIP5 models diverge (positively and negatively) from the moist pseudoadiabat by up to 2K at 300hPa. Precipitation weighted SSTs have recently been used to resolve the discrepancy between models and observations in upper tropospheric warming, but we show that they are not able to explain the differences in the mean state. While it is difficult to exactly depict the reasons for the inter-model spread, we demonstrate how the upper tropospheric lapse rate can deviate from the moist adiabat for the same lower tropospheric state with AMIP experiments. For this we use the ICON-A model, in which we tune convective and microphysical parameters. An improved understanding of the effect of different parameterisations on the models' lapse rates may help to better understand differences in the response to global warming.</p>

scholarly journals Climatological studies of lapse rates during summer months vis-à-vis All India Summer Monsoon Rainfall

MAUSAM ◽  
2021 ◽  
Vol 59 (1) ◽  
pp. 95-110
Author(s):  
U. R. JOSHI ◽  
G. S. PRAKASA RAO ◽  
SHRAVAN KUMAR
Keyword(s):  
Summer Monsoon ◽  
Monsoon Rainfall ◽  
Lower Troposphere ◽  
Summer Monsoon Rainfall ◽  
Lapse Rate ◽  
Upper Troposphere ◽  
India Summer Monsoon ◽  
India Summer Monsoon Rainfall ◽  
The Mean ◽  
Lapse Rates

The combined mean normal lapse rates for 0000 and 1200 UTC for 35 Radiosonde (RS) stations based on the period 1971-99 during the summer months (March to May) were worked out for standard levels and analysed.  To know whether any relationship exists between the distribution of summer lapse rates and the all India summer monsoon rainfall (June to September),  the mean lapse rates for three good monsoon years and six deficient years during the same period were worked out separately and the Lapse Rate Anomalies (LRAs) were examined in detail.  In excessive monsoon rainfall years the LRAs were generally negative (instable atmosphere) during summer months (March-May) in the lower and middle troposphere and the anomalies were positive in the upper troposphere.  In the deficient monsoon years, the case is reverse i.e., LRAs were positive in the lower troposphere (inhibiting the convective activity) while they were negative in the middle and upper troposphere.  The same results were noticed in the recent worst monsoon year 2002 and bad monsoon year 2004.   The LRAs thus give signals in the months of March to May regarding the ensuing monsoon rainfall qualitatively and can be used as one of the tools for long range forecasting.

Variations of Tropical Lapse Rates in Climate Models and their Implications for Upper Tropospheric Warming

2021 ◽  
pp. 1-50
Author(s):  
P. Keil ◽  
H. Schmidt ◽  
B. Stevens ◽  
J. Bao
Keyword(s):  
Climate Models ◽  
Atmospheric Model ◽  
Small Scale ◽  
Temperature Structure ◽  
Vertical Temperature ◽  
Upper Troposphere ◽  
Global Atmospheric Model ◽  
Lapse Rates ◽  
The Tropics ◽  
Physics Experiments

AbstractThe vertical temperature structure in the tropics is primarily set by convection and therefore follows a moist adiabat to first order. However, tropical upper tropospheric temperatures differ among climate models and observations, as atmospheric convection remains poorly understood. Here, we quantify the variations in tropical lapse rates in CMIP6 models and explore reasons for these variations. We find that differences in surface temperatures weighted by the regions of strongest convection cannot explain these variations and therefore we hypothesise that the representation of convection itself and associated small scale processes are responsible. We reproduce these variations in perturbed physics experiments with the global atmospheric model ICON-A, in which we vary autoconversion and entrainment parameters. For smaller autoconversion values, additional freezing enthalpy from the cloud water that is not precipitated warms the upper troposphere. Smaller entrainment rates also lead to a warmer upper troposphere, as convection and thus latent heating reaches higher. Furthermore, we show that according to most radiosonde datasets all CMIP6 AMIP simulations overestimate recent upper tropospheric warming. Additionally, all radiosonde datasets agree that climate models on average overestimate the amount of upper tropospheric warming for a given lower tropospheric warming. We demonstrate that increased entrainment rates reduce this overestimation, likely because of the reduction of latent heat release in the upper troposphere. Our results suggest that imperfect convection parameterisations are responsible for a considerable part of the variations in tropical lapse rates and also part of the overestimation of warming compared to the observations.

scholarly journals Reduced global warming from CMIP6 projections when weighting models by performance and independence

2020 ◽  
Vol 11 (4) ◽  
pp. 995-1012
Author(s):  
Lukas Brunner ◽  
Angeline G. Pendergrass ◽  
Flavio Lehner ◽  
Anna L. Merrifield ◽  
Ruth Lorenz ◽  
...  
Keyword(s):  
Climate Change ◽  
Retrospective Analysis ◽  
Climate Models ◽  
Cmip5 Models ◽  
Future Climate Change ◽  
Historical Period ◽  
Climate Change Scenarios ◽  
Uncertainty Range ◽  
Future Warming ◽  
The Mean

Abstract. The sixth Coupled Model Intercomparison Project (CMIP6) constitutes the latest update on expected future climate change based on a new generation of climate models. To extract reliable estimates of future warming and related uncertainties from these models, the spread in their projections is often translated into probabilistic estimates such as the mean and likely range. Here, we use a model weighting approach, which accounts for the models' historical performance based on several diagnostics as well as model interdependence within the CMIP6 ensemble, to calculate constrained distributions of global mean temperature change. We investigate the skill of our approach in a perfect model test, where we use previous-generation CMIP5 models as pseudo-observations in the historical period. The performance of the distribution weighted in the abovementioned manner with respect to matching the pseudo-observations in the future is then evaluated, and we find a mean increase in skill of about 17 % compared with the unweighted distribution. In addition, we show that our independence metric correctly clusters models known to be similar based on a CMIP6 “family tree”, which enables the application of a weighting based on the degree of inter-model dependence. We then apply the weighting approach, based on two observational estimates (the fifth generation of the European Centre for Medium-Range Weather Forecasts Retrospective Analysis – ERA5, and the Modern-Era Retrospective analysis for Research and Applications, version 2 – MERRA-2), to constrain CMIP6 projections under weak (SSP1-2.6) and strong (SSP5-8.5) climate change scenarios (SSP refers to the Shared Socioeconomic Pathways). Our results show a reduction in the projected mean warming for both scenarios because some CMIP6 models with high future warming receive systematically lower performance weights. The mean of end-of-century warming (2081–2100 relative to 1995–2014) for SSP5-8.5 with weighting is 3.7 ∘C, compared with 4.1 ∘C without weighting; the likely (66%) uncertainty range is 3.1 to 4.6 ∘C, which equates to a 13 % decrease in spread. For SSP1-2.6, the weighted end-of-century warming is 1 ∘C (0.7 to 1.4 ∘C), which results in a reduction of −0.1 ∘C in the mean and −24 % in the likely range compared with the unweighted case.

scholarly journals Net effect of the QBO in a chemistry climate model

2008 ◽  
Vol 8 (21) ◽  
pp. 6505-6525 ◽  
Author(s):  
H. J. Punge ◽  
M. A. Giorgetta
Keyword(s):  
General Circulation ◽  
Climate Models ◽  
Climate Model ◽  
Middle Atmosphere ◽  
Meridional Circulation ◽  
Vortex Formation ◽  
General Circulation Models ◽  
Quasi Biennial Oscillation ◽  
The Mean ◽  
The Tropics

Abstract. The quasi-biennial oscillation (QBO) of zonal wind is a prominent mode of variability in the tropical stratosphere. It affects not only the meridional circulation and temperature over a wide latitude range but also the transport and chemistry of trace gases such as ozone. Compared to a QBO less circulation, the long-term climatological means of these quantities are also different. These climatological net effects of the QBO can be studied in general circulation models that extend into the middle atmosphere and have a chemistry and transport component, so-called Chemistry Climate Models (CCMs). In this work we show that the CCM MAECHAM4-CHEM can reproduce the observed QBO variations in temperature and ozone mole fractions when nudged towards observed winds. In particular, it is shown that the QBO signal in transport of nitrogen oxides NOx plays an important role in reproducing the observed ozone QBO, which features a phase reversal slightly below the level of maximum of the ozone mole fraction in the tropics. We then compare two 20-year experiments with the MAECHAM4-CHEM model that differ by including or not including the QBO. The mean wind fields differ between the two model runs, especially during summer and fall seasons in both hemispheres. The differences in the wind field lead to differences in the meridional circulation, by the same mechanism that causes the QBO's secondary meridional circulation, and thereby affect mean temperatures and the mean transport of tracers. In the tropics, the net effect on ozone is mostly due to net differences in upwelling and, higher up, the associated temperature change. We show that a net surplus of up to 15% in NOx in the tropics above 10 hPa in the experiment that includes the QBO does not lead to significantly different volume mixing ratios of ozone. We also note a slight increase in the southern vortex strength as well as earlier vortex formation in northern winter. Polar temperatures differ accordingly. Differences in the strength of the Brewer-Dobson circulation and in further trace gas concentrations are analysed. Our findings underline the importance of a representation of the QBO in CCMs.

scholarly journals Validation of six years of TES tropospheric ozone retrievals with ozonesonde measurements: implications for spatial patterns and temporal stability in the bias

2013 ◽  
Vol 6 (5) ◽  
pp. 1413-1423 ◽  
Author(s):  
W. W. Verstraeten ◽  
K. F. Boersma ◽  
J. Zörner ◽  
M. A. F. Allaart ◽  
K. W. Bowman ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
A Priori ◽  
Temporal Stability ◽  
Lower Troposphere ◽  
Temporal Variations ◽  
Upper Troposphere ◽  
The World ◽  
The Difference ◽  
The Tropics

Abstract. In this analysis, Tropospheric Emission Spectrometer (TES) V004 nadir ozone (O3) profiles are validated with more than 4400 coinciding ozonesonde measurements taken across the world from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) during the period 2005–2010. The TES observation operator was applied to the sonde data to ensure a consistent comparison between TES and ozonesonde data, i.e. without the influence of the a priori O3 profile needed to regulate the retrieval. Generally, TES V004 O3 retrievals are biased high by 2–7 ppbv (7–15%) in the troposphere, consistent with validation results from earlier studies. Because of two degrees of freedom for signal in the troposphere, we can distinguish between upper and lower troposphere mean biases, respectively ranging from −0.4 to +13.3 ppbv for the upper troposphere and +3.9 to +6.0 ppbv for the lower troposphere. Focusing on the 464 hPa retrieval level, broadly representative of the free tropospheric O3, we find differences in the TES biases for the tropics (+3 ppbv, +7%), sub-tropics (+5 ppbv, +11%), and northern (+7 ppbv, +13%) and southern mid-latitudes (+4 ppbv, +10%). The relatively long-term record (6 yr) of TES–ozonesonde comparisons allowed us to quantify temporal variations in TES biases at 464 hPa. We find that there are no discernable biases in each of these latitudinal bands; temporal variations in the bias are typically within the uncertainty of the difference between TES and ozonesondes. Establishing these bias patterns is important in order to make meaningful use of TES O3 data in applications such as model evaluation, trend analysis, or data assimilation.

Regionally Varying Assessments of Upper-Level Tropical Width in Reanalyses and CMIP5 Models Using a Tropopause Break Metric

2020 ◽  
Vol 33 (14) ◽  
pp. 5885-5903 ◽  
Author(s):  
Elinor R. Martin ◽  
Cameron R. Homeyer ◽  
Roarke A. McKinzie ◽  
Kevin M. McCarthy ◽  
Tao Xian
Keyword(s):  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
The Past ◽  
East Pacific ◽  
Change Climate ◽  
Upper Level ◽  
The Tropics

AbstractChanges in tropical width can have important consequences in sectors including ecosystems, agriculture, and health. Observations suggest tropical expansion over the past 30 years although studies have not agreed on the magnitude of this change. Climate model projections have also indicated an expansion and show similar uncertainty in its magnitude. This study utilizes an objective, longitudinally varying, tropopause break method to define the extent of the tropics at upper levels. The location of the tropopause break is associated with enhanced stratosphere–troposphere exchange and thus its structure influences the chemical composition of the stratosphere. The method shows regional variations in the width of the upper-level tropics in the past and future. Four modern reanalyses show significant contraction of the tropics over the eastern Pacific between 1981 and 2015, and slight but significant expansion in other regions. The east Pacific narrowing contributes to zonal mean narrowing, contradicting prior work, and is attributed to the use of monthly and zonal mean data in prior studies. Six global climate models perform well in representing the climatological location of the tropical boundary. Future projections show a spread in the width trend (from ~0.5° decade−1 of narrowing to ~0.4° decade−1 of widening), with a narrowing projected across the east Pacific and Northern Hemisphere Americas. This study illustrates that this objective tropopause break method that uses instantaneous data and does not require zonal averaging is appropriate for identifying upper-level tropical width trends and the break location is connected with local and regional changes in precipitation.

scholarly journals Neutral Saturated Lapse Rate: An Experimental Check from CALJET-1998 and PACJET-2001

2009 ◽  
Vol 137 (12) ◽  
pp. 4382-4385 ◽  
Author(s):  
Renzo Richiardone ◽  
Massimiliano Manfrin
Keyword(s):  
High Resolution ◽  
Normal Distribution ◽  
Mean Value ◽  
Lapse Rate ◽  
Temperature Profiles ◽  
Experimental Check ◽  
Rate Distribution ◽  
The Mean ◽  
Lapse Rates ◽  
Good Agreement

Abstract The lapse rates of high-resolution temperature profiles during nearly neutral, saturated conditions are compared with the saturated adiabatic lapse rate and with that proposed by Richiardone and Giusti. A good agreement between the latter and the mean value of the observed lapse rate is found, whereas the saturated adiabatic lapse rate differs significantly, confirming experimentally that it is not completely correct to assess the moist neutrality from a comparison with the saturated adiabatic lapse rate. The lapse-rate distribution supports the hypothesis that the lapse-rate statistics is a local collection of saturated adiabatic lapse rates in a background normal distribution centered around the neutrality.

scholarly journals Impact of the Asian monsoon anticyclone on the variability of mid-to-upper tropospheric methane above the Mediterranean Basin

2014 ◽  
Vol 14 (20) ◽  
pp. 11427-11446 ◽  
Author(s):  
P. Ricaud ◽  
B. Sič ◽  
L. El Amraoui ◽  
J.-L. Attié ◽  
R. Zbinden ◽  
...  
Keyword(s):  
Mediterranean Basin ◽  
Near Infrared ◽  
Asian Monsoon ◽  
Climate Models ◽  
Transport Model ◽  
Lower Troposphere ◽  
Upper Troposphere ◽  
The Mediterranean ◽  
East West ◽  
The Mediterranean Basin

Abstract. The space and time variabilities of methane (CH4) total column and upper tropospheric mixing ratios are analysed above the Mediterranean Basin (MB) as part of the Chemical and Aerosol Mediterranean Experiment (ChArMEx) programme. Since the analysis of the mid-to-upper tropospheric CH4 distribution from spaceborne sensors and model outputs is challenging, we have adopted a climatological approach and have used a wide variety of data sets. We have combined spaceborne measurements from the Thermal And Near infrared Sensor for carbon Observations – Fourier Transform Spectrometer (TANSO-FTS) instrument on the Greenhouse gases Observing SATellite (GOSAT) satellite, the Atmospheric InfraRed Spectrometer (AIRS) on the AURA platform and the Infrared Atmospheric Sounder Interferometer (IASI) instrument aboard the MetOp-A platform with model results from the Chemical Transport Model (CTM) MOCAGE, and the Chemical Climate Models (CCMs) CNRM-AOCCM and LMDz-OR-INCA (according to different emission scenarios). In order to minimize systematic errors in the spaceborne measurements, we have only considered maritime pixels over the MB. The period of interest spans from 2008 to 2011 considering satellite and MOCAGE data and, regarding the CCMs, from 2001 to 2010. Although CH4 is a long-lived tracer with lifetime of ~12 years and is supposed to be well mixed in the troposphere, an east–west gradient in CH4 is observed and modelled in the mid-to-upper troposphere with a maximum in the Western MB in all seasons except in summer when CH4 accumulates above the Eastern MB. The peak-to-peak amplitude of the east–west seasonal variation in CH4 above the MB in the upper troposphere (300 hPa) is weak but almost twice as great in the satellite measurements (~25 ppbv) as in the model data (~15 ppbv). The maximum of CH4 in summer above the eastern MB can be explained by a series of dynamical processes only occurring in summer. The Asian monsoon traps and uplifts high amounts of CH4 to the upper troposphere where they build up. The Asian Monsoon Anticyclone redistributes these elevated CH4 amounts towards North Africa and the Middle East to finally reach and descend in the eastern MB. In the lower troposphere, the CH4 variability is mainly driven by the local sources of emission in the vicinity of the MB.

scholarly journals The Key Physical Parameters Governing Frictional Dissipation in a Precipitating Atmosphere

2013 ◽  
Vol 70 (9) ◽  
pp. 2916-2929 ◽  
Author(s):  
A. M. Makarieva ◽  
V. G. Gorshkov ◽  
A. V. Nefiodov ◽  
D. Sheil ◽  
A. D. Nobre ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Atmospheric Circulation ◽  
Lapse Rate ◽  
Small Scale ◽  
Dynamic Power ◽  
True Value ◽  
Frictional Dissipation ◽  
The Mean ◽  
Degree Of Condensation ◽  
The Tropics

Abstract Precipitation generates small-scale turbulent air flows—the energy of which ultimately dissipates to heat. The power of this process has previously been estimated to be around 2–4 W m−2 in the tropics: a value comparable in magnitude to the dynamic power of global atmospheric circulation. Here it is suggested that the true value is approximately half the value of this previous estimate. The result reflects a revised evaluation of the mean precipitation pathlength HP. The dependence of HP on surface temperature, relative humidity, temperature lapse rate, and degree of condensation in the ascending air were investigated. These analyses indicate that the degree of condensation, defined as the relative change of the saturated water vapor mixing ratio in the region of condensation, is a major factor determining HP. From this theory the authors develop an estimate indicating that the mean large-scale rate of frictional dissipation associated with total precipitation in the tropics lies between 1 and 2 W m−2 and show empirical evidence in support of this estimate. Under terrestrial conditions frictional dissipation is found to constitute a minor fraction of the dynamic power of condensation-induced atmospheric circulation, which is estimated to be at least 2.5 times larger. However, because HP increases with increasing surface temperature Ts, the rate of frictional dissipation would exceed the power of condensation-induced dynamics, and thus block major circulation, at Ts ≳ 320 K in a moist adiabatic atmosphere.

scholarly journals Regional Apparent Boundary Layer Lapse Rates Determined from CALIPSO and MODIS Data for Cloud-Height Determination

2014 ◽  
Vol 53 (4) ◽  
pp. 990-1011 ◽  
Author(s):  
Sunny Sun-Mack ◽  
Patrick Minnis ◽  
Yan Chen ◽  
Seiji Kato ◽  
Yuhong Yi ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Thermal Structure ◽  
Lower Troposphere ◽  
Free Water ◽  
Lapse Rate ◽  
Monthly Means ◽  
Spatial Error ◽  
Modis Data ◽  
Low Cloud ◽  
Lapse Rates

AbstractReliably determining low-cloud heights using a cloud-top temperature from satellite infrared imagery is often challenging because of difficulties in characterizing the local thermal structure of the lower troposphere with the necessary precision and accuracy. To improve low-cloud-top height estimates over water surfaces, various methods have employed lapse rates anchored to the sea surface temperature to replace the boundary layer temperature profiles that relate temperature to altitude. To further improve low-cloud-top height retrievals, collocated Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and Aqua Moderate Resolution Imaging Spectroradiometer (MODIS) data taken from July 2006 to June 2007 and from June 2009 to May 2010 (2 yr) for single-layer low clouds are used here with numerical weather model analyses to develop regional mean boundary apparent lapse rates. These parameters are designated as apparent lapse rates because they are defined using the cloud-top temperatures from satellite retrievals and surface skin temperatures; they do not represent true lapse rates. Separate day and night, seasonal mean lapse rates are determined for 10′-resolution snow-free land, water, and coastal regions, while zonally dependent lapse rates are developed for snow/ice-covered areas for use in the Clouds and the Earth’s Radiant Energy System (CERES) Edition 4 cloud property retrieval system (CCPRS-4). The derived apparent lapse rates over ice-free water range from 5 to 9 K km−1 with mean values of about 6.9 and 7.2 K km−1 during the day and night, respectively. Over land, the regional values vary from 3 to 8 K km−1, with day and night means of 5.5 and 6.2 K km−1, respectively. The zonal-mean apparent lapse rates over snow and ice surfaces generally decrease with increasing latitude, ranging from 4 to 8 K km−1. All of the CCPRS-4 lapse rates were used along with five other lapse rate techniques to retrieve cloud-top heights for 2 months of independent Aqua MODIS data. When compared with coincident CALIPSO data for October 2007, the mean cloud-top height differences between CCPRS-4 and CALIPSO during the daytime (nighttime) are 0.04 ± 0.61 km (0.10 ± 0.62 km) over ice-free water, −0.06 ± 0.85 km (−0.01 ± 0.83 km) over snow-free land, and 0.38 ± 0.95 km (0.03 ± 0.92 km) over snow-covered areas. The CCPRS-4 regional monthly means are generally unbiased and lack spatial error gradients seen in the comparisons for most of the other techniques. Over snow-free land, the regional monthly-mean errors range from −0.28 ± 0.74 km during daytime to 0.04 ± 0.78 km at night. The water regional monthly means are, on average, 0.04 ± 0.44 km less than the CALIPSO values during day and night. Greater errors are realized for snow-covered regions. Overall, the CCPRS-4 lapse rates yield the smallest RMS differences for all times of day over all areas both for individual retrievals and monthly means. These new regional apparent lapse rates, used in processing CERES Edition 4 data, should provide more accurate low-cloud-type heights than previously possible using satellite imager data.

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