Ultra-enhanced spring branch growth in CO 2 -enriched trees: can it alter the phase of the atmosphere's seasonal CO 2 cycle?

Abstract Since the early 1960s, the declining phase of the atmosphere's seasonal CO 2 cycle has advanced by approximately 7 days in northern temperate latitudes, possibly as a result of increasing temperatures that may be advancing the time of occurrence of what may be called 'climatological spring.' However, just as several different phenomena are thought to have been responsible for the concomitant increase in the amplitude of the atmosphere's seasonal CO 2 oscillation, so too may other factors have played a role in bringing about the increasingly earlier spring drawdown of CO 2 that has resulted in the advancement of the declining phase of the air's CO 2 cycle. One of these factors may be the ongoing rise in the CO 2 content of the air itself; for the aerial fertilization effect of this phenomenon may be significantly enhancing the growth of each new season's initial flush of vegetation, which would tend to stimulate the early drawdown of atmospheric CO 2 and thereby advance the time of occurrence of what could be called 'biological spring.' Working with sour orange (Citrus aurantium L.) trees that have been growing out-of-doors in open-top chambers for over 10 years in air of either 400 or 700 ppm CO 2 , this hypothesis was investigated by periodically measuring the lengths, dry weights and leaf chlorophyll concentrations of new branches that emerged from the trees at the start of the 1998 growing season. The data demonstrate that the hypothesis is viable, and that it might possibly account for 2 of the 7 days by which the spring drawdown of the air's CO 2 concentration has advanced over the past few decades

Diurnal patterns in lightning activity in northern tropical Africa

The study analyzes summertime lightning incidence data across northern tropical Africa from the TRMM satellite sensor during 1998-2011. It uses harmonic analyses to detect the spatial patterns in diurnal variations of lightning activity across the study area. The results are in conformity with previous studies examining diurnal patterns of convective weather processes in this region, with most lightning activity concentrated over land areas. The peak time of lightning activity over most of the study area was during late afternoon hours, from around 1700 to 1900 local standard time. The peak time of lightning activity was observed during early morning hours in some coastal areas, such as Cameroon, which can be a result of local-level convergence between the land and sea breeze. A general progression in the time of lightning activity from late afternoon to early evening hours was observed throughout the interior of the study area, which may be attributed to land-surface heating and associated mesoscale convective systems, and to upper-level circulation in the form of the African Easterly Jet Stream

Analysis of spatial patterns of trends in the frequency and intensity of Indian precipitation

We assembled daily precipitation records for 129 weather stations spread all over India for the time period 1910 to 2000. Next we classified these stations into nine different regions according to the mean annual precipitation values for the different India meteorological sub-divisions. We conducted detailed analysis of total precipitation and the frequency of precipitation for each five-percentile interval for every region.  In general, our results show a decrease in precipitation throughout much of India with only the northwest showing an increase. Our analyses by precipitation percentile class intervals show that the most extreme events have become more frequent, particularly in the western half of the country. Our results are broadly consistent with the IPCC Scientific Assessment by Houghton et al. (2001) and other studies focusing on the spatial dimensions of Indian precipitation over time.

Diurnal cycle of summer season thunderstorm activity in India

The diurnal cycle of tropical convection over the Indian region has been analysed in this study for the period of March to June from the thunderstorm reports of ground-based observatories throughout India during 2016-2020. The analyses indicate that during this period of the year, when the land progressively heats up diurnally, under conditions of deficient moisture, synoptic systems interact with the semi-permanent features of the atmosphere over the region to define areas of moisture and wind convergence, which in turn determine the frequency and diurnal cycle of thunderstorm activity. While the easterly and westerly waves are the major synoptic scale weather systems that affect the Indian region during March to May, the atmospheric changes are associated with the onset of the monsoon season in June. Amongst the semi-permanent features, the gradual intensification and migration of the shallow heat low to northwest India during May and June reinforce the western disturbances over this region, thereby intensifying the thunderstorm activity during the afternoon to evening hours over the western Himalayas and northwest Indian region. The role of the low-level anticyclones over the Arabian Sea and the Bay of Bengal is seen in the east-west-oriented moisture gradient across the Indian subcontinent which makes the east Indian subcontinent generally more prone to thunderstorm activity during this season. The east-west-oriented discontinuity line across north India is particularly intense during the morning hours along the foothills of the Himalayas. Its location directs moisture from the Bay of Bengal into the Himalayas causing early initiation of thunderstorm activity over the Himalayas. The discontinuity line moves southwards to the north Indian plains later in the day, although the western end becomes less marked. The north-south-oriented discontinuity line across the Indian subcontinent between the two anticyclones intensifies during the afternoon hours due to land heating and combines with the east-west wind discontinuity to become a T-shaped maximum convergence zone for thunderstorm activity during the afternoon hours over the Indian region, which intensifies as the months progress. With the onset of the southwest monsoon over the south peninsula and east Indian regions in June, the change in wind pattern from an easterly to a southwesterly flow regime over the south peninsula is reflected in an abrupt shift of the afternoon maximum of thunderstorm activity over the inland regions of the south peninsula to an early morning maximum over the southwest peninsular coast. Simultaneously, with the weakening of the anticyclone over the north Bay of Bengal and gradual strengthening of the southerly moisture flow into east and northeast India, there was in-phase increase in thunderstorm activity during the afternoon hours over the plains of east-central India, east India, and adjoining southern parts of northeast India during June. The diurnal pattern of tropical convection significantly affects human lives over the Indian subcontinent