High-resolution in situ observations of atmospheric thermodynamics using dropsondes during the Organization of Tropical East Pacific Convection (OTREC) field campaign

The Organization of Tropical East Pacific Convection (OTREC) field campaign investigated the dynamical structure of convection in the tropical east Pacific and Caribbean. One of the central data sets for this field campaign is the thermodynamic structure of the atmosphere measured by dropsondes released from the NSF/NCAR G-V research aircraft. Between 7 August and 2 October 2019, 648 dropsondes were successfully released from 22 research flights. Soundings were launched in a grid pattern with a typical spacing of 1∘ longitude and 1.2∘ latitude and provided profiles of pressure, temperature, humidity, and winds between the surface and on average 13.3 km. Of these soundings, 636 provided complete vertical profiles of all parameters with a nominal vertical resolution between 6 to 12 m from the surface to almost flight altitude. OTREC deployed the new NRD41 dropsonde, which is the most advanced model that has been developed at NCAR. Here, we describe the data set, the processing of the measurements, and general statistics of all dropsonde observations. The data set is available at https://doi.org/10.26023/EHRT-TN96-9W04 (UCAR/NCAR and Vömel, 2019).

Detection and tracking of tropical convective storms based on globally gridded precipitation measurements: Algorithm and Survey over the Tropics

This paper is the first attempt to document a simple convection tracking method based on the IMERG precipitation product to generate an IMERG-based Convection Tracking (IMERG-CT) dataset. Up to now precipitation datasets have been Eulerian accumulations. Now with IMERG-CT, we can estimate total rainfall based on Lagrangian accumulations, which is a very important step in diagnosing cloud-precipitation process following the evolution of air masses. Convection tracking algorithms have traditionally been developed based on brightness temperature (Tb) from satellite infrared (IR) retrievals. However, vigorous rainfall can be produced by warm-topped systems in moist environment, which cannot be captured by traditional IR-based tracking but is observed in IMERG-CT. Therefore, an advantage of IMERG-CT is its ability to include the previously missing information of shallow clouds that grow into convective storms, which provides us more complete lifecycle records of convective storms than traditional IR-based tracking does. This study also demonstrates the utility of IMERG-CT through investigating various properties of convective systems in terms of the evolution before and after peak precipitation rate and amount. For example, composite analysis reveals a link between evolution of precipitation and convective development: the signature of stratiform anvils remaining after the storm has produced the maximum rainfall, as average Tb stays almost constant for 5 hours after the peak of precipitation. Our study highlights the importance of joint analysis of cloud and precipitation data in time sequence, which helps elucidate the underlying dynamic processes producing tropical rainfall and its resultant effects on the atmospheric thermodynamics.

High-resolution in situ observations of atmospheric thermodynamics using dropsondes during the Organization of Tropical East Pacific Convection (OTREC) field campaign

The Organization of Tropical East Pacific Convection (OTREC) field campaign investigated the dynamical structure of convection in the tropical east Pacific and Caribbean. One of central data sets for this field campaign is the thermodynamic structure of the atmosphere measured by dropsondes released from the NSF/NCAR G V research aircraft. Between 7 August and 2 October 2019, 648 dropsonde were successfully released from twenty-two research flights. Soundings were launched in a grid pattern with a typical spacing of 1° longitude and 1.2° latitude and provide profiles of pressure, temperature, humidity, and winds between the surface and on average 13.3 km. Of these soundings, 636 provided complete vertical profiles of all parameters with a nominal vertical resolution between 6 to 12 m from the surface to almost flight altitude. OTREC deployed the new NRD41 dropsonde, which is the most advanced model that has been developed at NCAR. Here, we describe the data set, the processing of the measurements, and general statistics of all dropsonde observations. The dataset is available at https://doi.org/10.26023/EHRT-TN96-9W04 (UCAR/NCAR, 2019).

Van der Waals-like State Equation for Atmosphere

In this paper, we first analyze the atmosphere as a gas mixture per unit mass, which is governed by Van der Waals equation, considering the main components of the air and their respective critical properties (critical temperature TC and critical pressure pC ). After adjusting the corresponding constants and calling them I and D, we find Van der Waals state equation for the atmosphere in this context. Next, we analyze the order of magnitude of the terms in that equation and propose a Van der Waals-like form state equation depending only on D, which we call WD state equation. Additionally, we consider a physical approach for Van der Waals equation for the atmosphere, studying the pressure terms concerning intermolecular forces of repulsion and attraction in the air, and once again we find the previous WD state equation. With this new proposal, we verify that the potential temperature and the equivalent potential temperature hold for the same expressions as those set forth in atmospheric thermodynamics under the analysis of the ideal gas law. However, we discover corrections that depend on D in both the alternative form of the first law of thermodynamics and the virtual temperature.

Snowflake Selfies: A Low-Cost, High-Impact Approach toward Student Engagement in Scientific Research (with Their Smartphones)

An engaged scholarship project called “Snowflake Selfies” was developed and implemented in an upper-level undergraduate course at The Pennsylvania State University (Penn State). During the project, students conducted research on snow using low-cost, low-tech instrumentation that may be readily implemented broadly and scaled as needed, particularly at institutions with limited resources. During intensive observing periods (IOPs), students measured snowfall accumulations, snow-to-liquid ratios, and took microscopic photographs of snow using their smartphones. These observations were placed in meteorological context using radar observations and thermodynamic soundings, helping to reinforce concepts from atmospheric thermodynamics, cloud physics, radar, and mesoscale meteorology courses. Students also prepared a term paper and presentation using their datasets/photographs to hone communication skills. Examples from IOPs are presented. The Snowflake Selfies project was well received by undergraduate students as part of the writing-intensive course at Penn State. Responses to survey questions highlight the project’s effectiveness at engaging students and increasing their enthusiasm for the semester-long project. The natural link to social media broadened engagement to the community level. Given the successes at Penn State, we encourage Snowflake Selfies or similar projects to be adapted or implemented at other institutions.

Factors driving the Mediterranean water cycle from a cold and wet glacial past to a warm and dry future

<p>Model simulations of the last glacial maximum (LGM) and RCP8.5 projections suggest that factors responsible for past and future changes in the Mediterranean region are different.  The wet LGM conditions were determined mainly by low evaporation, with some increase of precipitation in the western areas, while dry rcp8.5 conditions will be driven by a reduction of precipitation over the whole region. These changes were caused by atmospheric dynamics (changes of mean atmospheric circulation ) in LGM and it will be caused by the atmospheric thermodynamics (reduction of mean moisture content ) in the future rcp8.5. In both cases, the Mediterranean region appears to be more sensitive to climate change than the rest of areas within the same latitudinal range, particularly considering the hydrological cycle, whose characteristics in winter exhibit large changes between these two different climates. These conclusions emerge from the substantial consensus among six PMIP3 and CMIP5 models, simulating LGM, pre-Industrial and rcp8.5 climate conditions.</p>