Role of sea surface warming in convective activity over Europe and Northern Eurasia: estimates with sensitivity model experiments

The influence of sea surface warming on convective activity over Europe and Northern Eurasia is estimated from sensitivity model experiments by an atmospheric general circulation model, ECHAM5, with prescribed boundary conditions ("warm" and "cold" sea surface). Convective activity is analysed by using various indices (thermodynamic, dynamic, and composite). It is shown that warmer sea surface leads to a general increase in the thermodynamic indices that is broadly consistent with observations. Particularly, the observed increase in CAPE over the eastern part of the Mediterranean Sea, the Black Sea, and Eastern Europe is well reproduced in the sensitivity experiments. At the same time, the shear and helicity instability indices depend little on sea surface warming. The experiment with only Mediterranean and Black Seas warming tends to overestimate the increase in the thermodynamic indices near these seas and underestimate the increase in the other regions. There are several regions (the Iberian Peninsula, Mongolia, and Northern China) where the observations show a decrease in the convective indices. These negative changes are not reproduced in the model experiments, because their nature is, apparently, not related to sea surface warming

An ensemble approach to simulate CO<inf>2</inf> emissions from natural fires

This paper presents ensemble simulations with the global climate model developed at the A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM). These simulations are forced by historical reconstructions of concentrations of well-mixed greenhouse gases (CO2, CH4, and N2O), sulfate aerosols (both in the troposphere and stratosphere), extent of crops and pastures, and total solar irradiance for AD 850-2005 (hereafter all years are taken as being AD) and by the Representative Concentration Pathway (RCP) scenarios for the same forcing agents until the year 2300. Our model implements GlobFIRM (Global FIRe Model) as a scheme for calculating characteristics of natural fires. Comparing to the original GlobFIRM model, in our implementation, the scheme is extended by a module accounting for CO2 release from soil during fires. The novel approach of our paper is to simulate natural fires in an ensemble fashion. Different ensemble members in the present paper are constructed by varying the values of parameters of the natural fires module. These members are constrained by the GFED-3.1 data set for the burnt area and CO2 release from fires and further subjected to Bayesian averaging. Our simulations are the first coupled model assessment of future changes in gross characteristics of natural fires. In our model, the present-day (1998-2011) global area burnt due to natural fires is (2.1 ± 0.4) × 106 km2 yr-1 (ensemble mean and intra-ensemble standard deviation are presented), and the respective CO2 emissions to the atmosphere are (1.4 ± 0.2) Pg C yr-1. The latter value is in agreement with the corresponding GFED estimates. The area burnt by natural fires is generally larger than the GFED estimates except in boreal Eurasia, where it is realistic, and in Australia, where it is smaller than these estimates. Regionally, the modelled CO2 emissions are larger (smaller) than the GFED estimates in Europe (in the tropics and north-eastern Eurasia). From 1998-2011 to 2091-2100, the ensemble mean global burnt area is increased by 13% (28%, 36%, 51%) under scenario RCP 2.6 (RCP 4.5, RCP 6.0, RCP 8.5). The corresponding global emissions increase is 14% (29%, 37%, 42%). From 2091-2100 to 2291-2300, under the mitigation scenario RCP 2.6 the ensemble mean global burnt area and the respective CO2 emissions slightly decrease, both by 5% relative to their values in the period 2091-2100. In turn, under scenario RCP 4.5 (RCP 6.0, RCP 8.5) the ensemble mean burnt area in the period 2291-2100 is higher by 15% (44%, 83%) than its mean value, and the ensemble mean CO2 emissions are correspondingly higher by 9% (19%, 31%). The simulated changes of natural fire characteristics in the 21st-23rd centuries are associated mostly with the corresponding changes in boreal regions of Eurasia and North America. However, under the RCP 8.5 scenario, the increase of the burnt area and CO2 emissions in boreal regions during the 22nd and 23rd centuries is accompanied by the respective decreases in the tropics and subtropics

Scheme for calculation of multi-layer cloudiness and precipitation for climate models of intermediate complexity

In this study we present a scheme for calculating the characteristics of multi-layer cloudiness and precipitation for Earth system models of intermediate complexity (EMICs). This scheme considers three-layer stratiform cloudiness and single-column convective clouds. It distinguishes between ice and droplet clouds as well. Precipitation is calculated by using cloud lifetime, which depends on cloud type and phase as well as on statistics of synoptic and convective disturbances. The scheme is tuned to observations by using an ensemble simulation forced by the ERA-40-derived climatology for 1979-2001. Upon calibration, the scheme realistically reproduces basic features of fields of cloud fractions, cloud water path, and precipitation. The simulated globally and annually averaged total cloud fraction is 0.59, and the simulated globally averaged annual precipitation is 100 cm yr?1. Both values agree with empirically derived values. The simulated cloud water path is too small, probably because the simulated vertical extent of stratiform clouds is too small. Geographical distribution and seasonal changes of calculated cloud fraction and precipitation are broadly realistic as well. However, some important regional biases still remain in the scheme, e.g. too little precipitation in the tropics. We discuss possibilities for future improvements in the scheme. © Author(s) 2013. CC Attribution 3.0 License

An Empirical Relationship among Characteristics of Severe Convective Storms, Their Cloud-Top Properties and Environmental Parameters in Northern Eurasia

Severe convective storms that produce tornadoes and straight-line winds usually develop under particular environmental conditions and have specific signatures on the cloud tops associated with intense updrafts. In this study, we performed a comparative analysis of satellite-derived characteristics, with a focus on cloud-top properties, and ERA5-based environmental parameters of convective storms in forested regions of the western part of Northern Eurasia in 2006&ndash;2021. The analyzed sample includes 128 different convective storms that produced 138 tornadoes and 143 linear windstorms. We found most tornadoes and linear windstorms are generated by quasi-linear convective storms or supercells. Such supercells form under lower convective instability and precipitable water content compared to those for other types of storms. We found a significant negative correlation of minimum temperature on the storm cloud top with instability parameters. In turn, the longevity of convective storms significantly correlates with wind shear and storm-relative helicity. About half of the tornadoes and 2/3 of linear windstorms are associated with the presence of cloud-top signatures, such as overshooting tops, cold-ring or cold U/V features. The events associated with such signatures are formed under high values of instability parameters. Our results can be used for further analysis of peculiarities of tornado and linear windstorm formation and to enhance the predictability of such severe events, especially in regions with a lack of weather radar coverage

Climatology of cloud overlap parameter

Cloud overlap parameter α was estimated on remote sensing data. This parameter is a measure of the relative weight of maximum (α = 1) and random (α = 0) overlap, and may be used to diagnose relative contribution of convective and stratiform cloudiness to total cloud fraction. Cloud overlap parameter α was calculated on passive satellite data MODIS and CERES for total cloud fraction; for both cases the vertical structure of cloud was assessed by using active satellite data CALIPSO. The global annual mean α is 0.36 (for CERES) and 0.26 (for MODIS), which points to the dominance of random overlap. Values of α are higher over land than over the ocean. The most prominent annual cycle of α is noted in the monsoon regions where α is close to 1 in winter and almost 0 in summer. The maximum cloud overlap is associated with small values of cloud fraction and occurs in subtropical highs over the ocean and in subtropical and polar deserts over land. The random cloud overlap occurs in regions with large values of cloud fraction (e.g., ITCZ and midlatitudinal storm tracks). Midlatitude oceanic lows are characterized by negative values of α, mostly in summer. Presumably, the assumption of the minimum overlap of cloud layers should be used in these regions due to strong baroclinic instability and horizontal shift of cloud layers

Climatology of Total Cloudiness in the Arctic: An Intercomparison of Observations and Reanalyses

Total cloud fraction over the Arctic (north of 60°N) has been evaluated and intercompared based on 16 Arctic cloud climatologies from different satellite and surface observations and reanalyses. The Arctic annual-mean total cloud fraction is about 0.70±0.03 according to different observational data. It is greater over the ocean (0.74±0.04) and less over land (0.67±0.03). Different observations for total cloud fraction are in a better agreement in summer than in winter and over the ocean than over land. An interannual variability is higher in winter than in summer according to all observations. The Arctic total cloud fraction has a prominent annual cycle according to most of the observations. The time of its maximum concurs with the time of the sea ice extent minimum (early summer–late autumn) and vice versa (late spring). The main reason for the discrepancies among observations is the difference in the cloud-detection algorithms, especially when clouds are detected over the ice/snow surface (during the whole year) or over the regions with the presence of strong low-tropospheric temperature inversions (mostly in winter). Generally, reanalyses are not in a close agreement with satellite and surface observations of cloudiness in the Arctic

La Patrie : journal quotidien, politique, commercial et littéraire

15 mars 18731873/03/15 (A33)

An ensemble approach to simulate CO<inf>2</inf> emissions from natural fires

This paper presents ensemble simulations with the global climate model developed at the A. M. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences (IAP RAS CM). These simulations are forced by historical reconstructions of concentrations of well-mixed greenhouse gases (CO2, CH4, and N2O), sulfate aerosols (both in the troposphere and stratosphere), extent of crops and pastures, and total solar irradiance for AD 850-2005 (hereafter all years are taken as being AD) and by the Representative Concentration Pathway (RCP) scenarios for the same forcing agents until the year 2300. Our model implements GlobFIRM (Global FIRe Model) as a scheme for calculating characteristics of natural fires. Comparing to the original GlobFIRM model, in our implementation, the scheme is extended by a module accounting for CO2 release from soil during fires. The novel approach of our paper is to simulate natural fires in an ensemble fashion. Different ensemble members in the present paper are constructed by varying the values of parameters of the natural fires module. These members are constrained by the GFED-3.1 data set for the burnt area and CO2 release from fires and further subjected to Bayesian averaging. Our simulations are the first coupled model assessment of future changes in gross characteristics of natural fires. In our model, the present-day (1998-2011) global area burnt due to natural fires is (2.1 ± 0.4) × 106 km2 yr-1 (ensemble mean and intra-ensemble standard deviation are presented), and the respective CO2 emissions to the atmosphere are (1.4 ± 0.2) Pg C yr-1. The latter value is in agreement with the corresponding GFED estimates. The area burnt by natural fires is generally larger than the GFED estimates except in boreal Eurasia, where it is realistic, and in Australia, where it is smaller than these estimates. Regionally, the modelled CO2 emissions are larger (smaller) than the GFED estimates in Europe (in the tropics and north-eastern Eurasia). From 1998-2011 to 2091-2100, the ensemble mean global burnt area is increased by 13% (28%, 36%, 51%) under scenario RCP 2.6 (RCP 4.5, RCP 6.0, RCP 8.5). The corresponding global emissions increase is 14% (29%, 37%, 42%). From 2091-2100 to 2291-2300, under the mitigation scenario RCP 2.6 the ensemble mean global burnt area and the respective CO2 emissions slightly decrease, both by 5% relative to their values in the period 2091-2100. In turn, under scenario RCP 4.5 (RCP 6.0, RCP 8.5) the ensemble mean burnt area in the period 2291-2100 is higher by 15% (44%, 83%) than its mean value, and the ensemble mean CO2 emissions are correspondingly higher by 9% (19%, 31%). The simulated changes of natural fire characteristics in the 21st-23rd centuries are associated mostly with the corresponding changes in boreal regions of Eurasia and North America. However, under the RCP 8.5 scenario, the increase of the burnt area and CO2 emissions in boreal regions during the 22nd and 23rd centuries is accompanied by the respective decreases in the tropics and subtropics