In the vast expanse of our atmosphere, there are fascinating phenomena that can have profound implications for our climate and weather patterns. One such phenomenon is tropopause-overshooting convection, a process in which convection soars through the tropopause, carrying air from the lower troposphere to the lower stratosphere. The exchange of air between these layers can significantly influence the composition, radiation, and chemistry of the upper troposphere and lower stratosphere.
What is Tropopause-Overshooting Convection?
Tropopause-overshooting convection refers to the upward movement of air within thunderstorms that surpasses the tropopause, a boundary between the troposphere and the stratosphere. Typically, thunderstorms exist within the lowest layer of the atmosphere, known as the troposphere. However, under certain conditions, these thunderstorms can extend into the stratosphere, carrying air from the troposphere to the stratosphere.
This upward transport of air introduces a mixing of air masses from different altitudes, resulting in complex interactions and influences on our atmosphere. To comprehend the role tropopause-overshooting convection plays in the transport of trace gases across the tropopause, a recent research study conducted a comprehensive ten-year analysis of overshooting convection in the eastern two-thirds of the contiguous United States.
How is GridRad Data Used in the Analysis?
The study utilized a dataset called GridRad, which provides high-resolution radar reflectivity data merged from observations obtained by radars in the National Oceanic and Atmospheric Administration Next Generation Weather Radar (NEXRAD) network. By creating three-dimensional gridded radar reflectivity fields, the researchers estimated the altitude of echo tops, or the highest points of these storm clouds, at hourly intervals throughout the analysis period from 2004 to 2013.
Comparisons were then made between the estimated echo top altitudes and tropopause altitudes derived from the ERA-Interim reanalysis. This approach allowed the researchers to identify instances of overshooting convection, where the echo tops surpassed the tropopause. By analyzing a vast geographical region with a high level of detail, the study sought to uncover patterns and trends in the occurrence of overshooting events.
Where is Overshooting Convection Most Common?
The analysis revealed that overshooting convection is most prevalent in the central United States, with a secondary maximum along the southeast coast. These regions experience a pronounced frequency of storms that extend beyond the tropopause, consequently facilitating the transport of air between the troposphere and the stratosphere.
The abundance of overshooting events in these areas signifies the influential role that convection plays in regulating the exchange of air masses across the tropopause. Understanding these geographic preferences provides crucial insights into the interplay between convective activity and the upper layers of our atmosphere.
When Do Most Overshooting Events Occur?
An intriguing finding from the research is the consistent time window for maximum overshooting events. Between 2200 and 0200 UTC, the peak activity of tropopause-overshooting convection occurs. This time period aligns with the nighttime hours across the contiguous United States, suggesting the influence of specific atmospheric conditions during this period that favor overshooting events.
Additionally, the analysis revealed a seasonal dependence, with the majority of overshooting events occurring in May, June, and July. These months coincide with the period when convection is most vigorous, reaching deeper vertical extents, significantly impacting the tropopause in terms of altitude and composition. The relatively low tropopause altitude during these months creates favorable conditions for convection to surge into the stratosphere.
How Does Overshooting Convection Impact the Upper Troposphere and Lower Stratosphere?
Overshooting convection has significant implications for the upper troposphere and lower stratosphere (UTLS). The transport of air masses across the tropopause brings together different compositions and chemical constituents from distinct regions of the atmosphere, thereby influencing the chemistry and radiation balance of the UTLS.
By introducing lower tropospheric air into the stratosphere, overshooting convection affects the distribution of trace gases, including pollutants, greenhouse gases, and natural substances. This process can alter the atmospheric composition, directly influencing climate patterns and air quality.
Furthermore, the mixing of air masses facilitated by overshooting convection can impact the formation of clouds and the distribution of aerosols in the UTLS. These factors, in turn, have implications for radiative forcing, the balance between incoming solar radiation and outgoing terrestrial radiation, affecting Earth’s energy budget and ultimately contributing to climate change.
Takeaways
Tropopause-overshooting convection plays a crucial role in the transport of air masses between the troposphere and the stratosphere, with implications for the chemistry, radiation, and composition of the upper troposphere and lower stratosphere. The extensive ten-year analysis of overshooting convection in the contiguous United States provided valuable insights into the spatial and temporal occurrence of these events.
Understanding the patterns and conditions that favor overshooting convection enhances our knowledge of the processes shaping our atmosphere and their consequences for our climate. As we continue to study and monitor these dynamics, we gain a deeper understanding of the delicate balance within Earth’s atmosphere, enabling us to make informed decisions and take necessary actions to safeguard our planet’s well-being.
Sources:
Cooney, J. W., Bowman, K. P., Homeyer, C. R., & Fenske, T. M. (2018). Ten Year Analysis of Tropopause-Overshooting Convection Using GridRad Data. Journal of Geophysical Research: Atmospheres. https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017JD027718
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