Reply to comment by Ben-Zvi,A., D. Rosenfeld and A. Givati on the paper: Levin,Z., N. Halfon and P. Alpert, “Reassessment of rain experiments and operations in Israel including synoptic considerations,” Atmos. Res. 97, 513–525. DOI: 10.1016/j.atmosres.2010.06.011

Levin et al. (2010; hereafter LHA) (Levin, Z., Halfon, N., Alpert, P., 2010. Reassessment of rain experiments and operations in Israel including synoptic considerations. Atmos. Res. 97, 513–525. DOI:10.1016/j.atmosres.2010.06.011.), reanalyzed the results of the operational seeding in northern Israel between 1975 and 2007 and the preceding Israel 2 cloud seeding experiment (1969–1975) and concluded that there is no net increase in precipitation over the target areas. Our analysis revealed that a synoptic bias during Israel 2 is one of the reasons for the apparent positive effect of seeding in the northern target area and the negative effect in the southern area both of which disappeared in the following experiment in the south (Israel 3; 1975–1995) and the operational seeding in the north.Ben-Zvi et al. (2010;hereafter BRG) criticized our paper primarily on the ground that we did not consider the positive results of Israel 1 experiment (1960–1967). It should be noted that in Israel 1 different seeding lines were used from those in both Israel 2 and the operational period. In addition, its raw data is not accessible anymore for reanalysis. Furthermore, Israel 2 had been designed as a confirmatory cross-over experiment to Israel 1 and failed to reproduce its promising results with double ratio (DR) of ~ 1.00, namely, zero rainfall enhancements. The same DR values were also found in Israel 3 and in the operational seeding. Therefore, because of the differences in the two experiments, the lack of access to the raw data and the disappointing results of the confirmatory experiment, we decided to concentrate our analysis on the more recent seeding activities.The attempt by BRG to explain the reduction of the DR to ~ 1.00 in the operational seeding period by the suppression due to pollution have been disproved by Alpert et al., 2008, Alpert et al., 2009 and also fail to explain the sharp decline of the target/control ratio right at the beginning of the operational seeding period when the lucky draw in this area came to its end (see LHA).     

Comment on “Trends and low frequency variability of extra-tropical cyclone activity in the ensemble of twentieth century reanalysis” by Xiaolan L. Wang,Y. Feng,G. P. Compo,V. R. Swail,F. W. Zwiers,R. J. Allan,and P. D. Sardeshmukh,Climate Dynamics, 2012

The main subject of this article is to comment on the issue of storminess trends derived from the twentieth century reanalysis (20CR) and from observations in the North Atlantic region written about in Wang et al. (Clim Dyn 40(11–12):2775–2800, 2012). The statement that the 20CR estimates would be consistent with storminess derived from pressure-based proxies does not hold for the time prior to 1950.     

El Chichón – influence on aerosol optical depth and direct,diffuse and total solar irradiances at Vancouver,B.C.

Abstract

Solar radiation data for Vancouver, B.C. were used to determine the increase in aerosol optical depth and the changes in the total, direct, diffuse and net short‐wave radiation fluxes associated with the presence of aerosol that originated from the eruption of El Chichón (Mexico) in April 1982. The aerosol optical depth increased by 400% resulting in reductions of 33% in the direct and increases of 80% in the diffuse short‐wave radiation. These maximum changes were experienced some 9 months following the eruption. The relative insensitivity of the total short‐wave radiation (maximum reduction was 6%) suggests that the volcanic cloud was a strong forward scatterer rather than an absorber or back scatterer. Moreover, interannual variability in the surface albedo and a negative feedback associated with the dependence of the surface albedo on the directionality of the incident radiation resulted in no consistent change in the amount of short‐wave radiation absorbed by the Earth's surface.     

“Reporting on climate change: A computational analysis of U.S. newspapers and sources of bias, 1997–2017”

News organizations constitute key sites of science communication between experts and lay audiences, giving many individuals their basic worldview of complex topics like climate change. Previous researchers have studied climate change news coverage to assess accuracy in reporting and potential sources of bias. These studies typically rely on manually coding articles from a handful of prestigious outlets, not allowing comparisons with smaller newspapers or providing enough diversity to assess the influence of partisan orientation or localized climate vulnerability on content production. Making these comparisons, this study indicates that partisan orientation, scale of circulation, and vulnerability to climate change correlate with several topics present in U.S. newspaper coverage of climate change. After assembling a corpus of over 78,000 articles covering two decades from 52 U.S. newspapers that are diverse in terms of geography, partisan orientation, scale of circulation, and objectively measured climate risk, a coherent set of latent topics were identified via an automated content analysis of climate change news coverage. Topic model results indicate that while outlet bias does not appear to impact the prevalence of coverage for most topics surrounding climate change, differences were evident for some topics based on partisan orientation, scale, or vulnerability status, particularly those relating to climate change denial, impacts, mitigation, or resource use. Overall, this paper provides a comprehensive study of U.S. newspaper coverage of climate change and identifies specific topics where outlet bias constitutes an important contextual factor.     

Tropical Cyclones and Polar Lows: Velocity, Size, and Energy Scales, and Relation to the 26℃ Cyclone Origin Criteria

The goal of this paper is to quantitatively formulate some necessary conditions for the development of intense atmospheric vortices. Specifically, these criteria are discussed for tropical cyclones (TC) and polar lows (PL) by using bulk formulas for fluxes of momentum, sensible heating, and latent heating between the ocean and the atmosphere. The velocity scale is used in two forms: (1) as expressed through the buoyancy flux b and the Coriolis parameter lc for rotating fluids convection, and (2) as expresse...     

Preface to the Special Issue:Predictability,Data Assimilation,and Dynamics of High Impact Weather-In Memory of Dr.Fuqing ZHANG

It has been two and a half years since Fuqing ZHANG,a distinguished professor in the Department of Meteorology and Atmospheric Science at the Pennsylvania State University(PSU),passed away unexpectedly on 19 July 2019.This special issue is to commemorate Prof.Fuqing ZHANG,who has made tremendous contributions on predictability,data assimilation,and the dynamics of high impact weather.     

Tropical cyclones and polar lows: Velocity,size, and energy scales,and relation to the 26°C cyclone origin criteria

The goal of this paper is to quantitatively formulate some necessary conditions for the development of intense atmospheric vortices. Specifically, these criteria are discussed for tropical cyclones (TC) and polar lows (PL) by using bulk formulas for fluxes of momentum, sensible heating, and latent heating between the ocean and the atmosphere. The velocity scale is used in two forms: (1) as expressed through the buoyancy flux b and the Coriolis parameter l_c for rotating fluids convection, and (2) as expressed with the cube of velocity times the drag coefficient through the formula for total kinetic energy dissipation in the atmospheric boundary layer. In the quasistationary case the dissipation equals the generation of the energy. In both cases the velocity scale can be expressed through temperature and humidity differences between the ocean and the atmosphere in terms of the reduced gravity, and both forms produce quite comparable velocity scales. Using parameters b and l_c, we can form scales of the area and, by adding the mass of a unit air column, a scale of the total kinetic energy as well. These scales nicely explain the much smaller size of a PL, as compared to a TC, and the total kinetic energy of a TC is of the order 10¹⁸-10¹⁹ J. It will be shown that wind of 33 m s^-1 is produced when the total enthalpy fluxes between the ocean and the atmosphere are about 700 W m^-2 for a TC and 1700 W m^-2 for a PL, in association with the much larger role of the latent heat in the first case and the stricter geostrophic constraints and larger static stability in the second case. This replaces the mystical role of 26^oC as a criterion for TC origin. The buoyancy flux, a product of the reduced gravity and the wind speed, together with the atmospheric static stability, determines the rate of the penetrating convection. It is known from the observations that the formation time for a PL reaching an altitude of 5--6 km can be only a few hours, and a day, or even half a day, for a TC reaching 15--18 km. These two facts allow us to construct curves on the plane of T^s and ΔT=T_s-T_a to determine possibilities for forming an intense vortex. Here, T_a is the atmospheric temperature at the height z=10 m. A PL should have ΔT>20^oC in accordance with the observations and numerical simulations. The conditions for a TC are not so straightforward but our diagram shows that the temperature difference of a few degrees, or possibly even a fraction of a degree, might be sufficient for TC development for a range of static stabilities and development times.     

Tropical Cyclones and Polar Lows: Velocity, Size,and Energy Scales, and Relation to the 26°C Cyclone Origin Criteria

The goal of this paper is to quantitatively formulate some necessary conditions for the development of intense atmospheric vortices. Specifically, these criteria are discussed for tropical cyclones (TC) and polar lows (PL) by using bulk formulas for fluxes of momentum, sensible heating, and latent heating between the ocean and the atmosphere. The velocity scale is used in two forms: (1) as expressed through the buoyancy flux b and the Coriolis parameter lc for rotating fluids convection, and (2) as expressed with the cube of velocity times the drag coefficient through the formula for total kinetic energy dissipation in the atmospheric boundary layer. In the quasistationary case the dissipation equals the generation of the energy. In both cases the velocity scale can be expressed through temperature and humidity differences between the ocean and the atmosphere in terms of the reduced gravity, and both forms produce quite comparable velocity scales. Using parameters b and lc., we can form scales of the area and, by adding the mass of a unit air column, a scale of the total kinetic energy as well. These scales nicely explain the much smaller size of a PL, as compared to a TC, and the total kinetic energy of a TC is of the order 1018 - 1019 J. It will be shown that wind of 33 m s-1 is produced when the total enthalpy fluxes between the ocean and the atmosphere are about 700 W m-2 for a TC and 1700 W m-2 for a PL, in association with the much larger role of the latent heat in the first case and the stricter geostrophic constraints and larger static stability in the second case. This replaces the mystical role of 26~C as a criterion for TC origin. The buoyancy flux, a product of the reduced gravity and the wind speed, together with the atmospheric static stability, determines the rate of the penetrating convection. It is known from the observations that the formation time for a PL reaching an altitude of 5-6 km can be only a few hours, and a day, or even half a day, for a TC reaching 15-18 km. These two facts allow us to construct curves on the plane of Ts and △T= Ts - Ta to determine possibilities for forming an intense vortex. Here, Ta is the atmospheric temperature at the height z = 10 m. A PL should have △T > 20℃ in accordance with the observations and numerical simulations. The conditions for a TC are not so straightforward but our diagram shows that the temperature difference of a few degrees, or possibly even a fraction of a degree, might be sufficient for TC development for a range of static stabilities and development times.     

Development and Validation of an Evaporation Duct Model.Part Ⅰ:Model Establishment and Sensitivity Experiments

Based on the Coupled Ocean-Atmospheric Response Experiment（COARE）bulk algorithm and the Naval Postgraduate School（NPS）model,a universal evaporation duct（UED）model that can flexibly accommodate the latest improvements in component（such as stability function,velocity roughness,and scalar roughness）schemes for different stratification and wind conditions,is proposed in this paper.With the UED model,the sensitivity of the model-derived evaporation duct height（EDH）to stability function（Ψ）,ocean wave effect under moderate to high wind speeds,and scalar roughness length parameterization,is investigated,and relative contributions of these factors are compared.The results show that the stability function is a key factor influencing the simulated EDH values.Under unstable conditions,the EDH values from stability functions of Fairall et al.（1996）and Hu and Zhang（1992）are generally higher than those from others;while under stable conditions,unreasonably high EDHs can be avoided by use of the stability functions of Hu and Zhang（1992）and Grachev et al.（2007）.Under moderate to high wind speeds,the increase in velocity roughness length z₀ due to consideration of the true ocean wave effect acts to reduce modeled EDH values;this trend is more pronounced under stable conditions.Although the scalar roughness length parameterization has a minor effect on the model-derived EDH,a positive correlation is found between the scalar roughness length z_0qand the model-derived EDH.     

Governing geoengineering research: why, when and how?

Research on geoengineering – deliberate management of the Earth’s climate system – is being increasingly discussed within the science and policy communities. While justified as necessary in order to expand the range of options available to policy makers in the future, geoengineering research has already engendered public controversy. Proposed projects have been protested or cancelled, and calls for a governance framework abound. In this paper, we consider the reasons why geoengineering research might be subject to additional governance and suggest mechanisms that might be usefully applied in developing such a framework. We consider criteria for governance as raised by a review of the growing literature on geoengineering and other controversial scientific topics. We suggest three families of concern that any governance research framework must respond to: the direct physical risks of the research; the transparency and responsibility in decision making for the research; and the larger societal meanings of the research. We review what mechanisms might be available to respond to these three families of concern, and consider how these might apply to geoengineering research.     

Global warming vs. climate change, taxes vs. prices: Does word choice matter?

Does ??climate change?? seem like a less serious problem than ??global warming?? to Americans and Europeans? Does describing the costs of climate change mitigation in terms of ??higher taxes?? instead of ??higher prices?? reduce public support for such efforts? In an experiment embedded in an American national survey, respondents were randomly assigned to rate the seriousness of ??global warming,?? ??climate change,?? or ??global climate change.?? Contrary to predictions made by a leading political strategist, the full sample and political Independents perceived ??climate change?? and ??global warming?? to be equally serious. Among Republicans, ??climate change?? was perceived to be more serious than ??global warming,?? whereas the reverse was true among Democrats. A similar experiment embedded in a survey of residents of 31 European countries showed that ??global warming?? and ??climate change?? were perceived to be equally serious problems. And an experiment embedded in an American survey showed that describing the increased costs of climate change mitigation legislation via ??higher taxes?? instead of via ??higher prices?? did not reduce popular support for such legislation, also contradicting a political strategy memo. Thus, word choice may sometimes affect public perceptions of the climate change seriousness or support for mitigation policies, but a single choice of terminology may not influence all people the same way, making strategic language choices difficult to implement.     

Dynamical and Thermal Problems in Vortex Development and Movement. Part I: A PV–Q View

Based on the Lagrangian change equation of vertical vorticity deduced from the equation of threedimensional Ertel potential vorticity(PV e),the development and movement of vortex are investigated from the view of potential vorticity and diabatic heating(PV-Q).It is demonstrated that the asymmetric distribution in the vortex of the non-uniform diabatic heating in both vertical and horizontal can lead to the vortex’s development and movement.The theoretical results are used to analyze the development and movement of a Tibetan Plateau(TP) vortex(TPV),which appeared over the TP,then slid down and moved eastward in late July 2008,resulting in heavy rainfall in Sichuan Province and along the middle and lower reaches of the Yangtze River.The relative contributions to the vertical vorticity development of the TPV are decomposed into three parts:the diabatic heating,the change in horizontal component of PV e(defined as PV 2),and the change in static stability θ z.The results show that in most cases,diabatic heating plays a leading role,followed by the change in PV 2,while the change of θ z usually has a negative impact in a stable atmosphere when the atmosphere becomes more stable,and has a positive contribution when the atmosphere approaches neutral stratification.The intensification of the TPV from 0600 to 1200 UTC 22 July 2008 is mainly due to the diabatic heating associated with the precipitation on the eastern side of the TPV when it uplifted on the up-slope of the northeastern edge of the Sichuan basin.The vertical gradient of diabatic heating makes positive(negative) PV e generation below(above) the maximum of diabatic heating;the positive PV e generation not only intensifies the low-level vortex but also enhances the vertical extent of the vortex as it uplifts.The change in PV e due to the horizontal gradient of diabatic heating depends on the vertical shear of horizontal wind that passes through the center of diabatic heating.The horizontal gradient of diabatic heating makes positive(negative) PV e generation on the right(left) side of the vertical shear of horizontal wind.The positive PV e generation on the right side of the vertical shear of horizontal wind not only intensifies the local vertical vorticity but also affects direction of movement of the TPV.These diagnostic results are in good agreement with the theoretic results developed from the PV-Q view.     

Climate,conflict, and social stability: what does the evidence say?

Are violent conflict and socio-political stability associated with changes in climatological variables? We examine 50 rigorous quantitative studies on this question and find consistent support for a causal association between climatological changes and various conflict outcomes, at spatial scales ranging from individual buildings to the entire globe and at temporal scales ranging from an anomalous hour to an anomalous millennium. Multiple mechanisms that could explain this association have been proposed and are sometimes supported by findings, but the literature is currently unable to decisively exclude any proposed pathway. Several mechanisms likely contribute to the outcomes that we observe.